Researchers Database

YUSA Yoichi

FacultyVice President
PositionVice President
Last Updated :2022/10/06


Profile and Settings

  • Name (Japanese)

  • Name (Kana)



  • Science, Kyoto University

Research Areas

  • Environmental science/Agricultural science, Conservation science (plants)
  • Environmental science/Agricultural science, Conservation science (plants)
  • Life sciences, Evolutionary biology
  • Life sciences, Ecology and environmental science

Research Experience

  • 2007, 2011, :奈良女子大学 准教授
  • 2011, -:奈良女子大学 教授
  • 2011, -:Professor, Nara Women's University
  • 2003, 2007, :奈良女子大学 助教授
  • 2003, 2007, :Nara Women's University, Associate Professor
  • 2001, 2003, :九州沖縄農業研究センター 主任研究官
  • 2001, 2003, :National Agricultural Research Center for Kyushu Okinawa Region, Senior Researcher
  • 1996, 2001, :九州農業試験場 研究員
  • 1996, 2001, :Kyushu National Agricultural Experiment Station, Researcher


  • 1995, Kyoto University, 理学研究科, 動物学専攻, Japan


Published Papers

  • Refereed, Journal of Theoretical Biology, Elsevier BV, Evolutionary game of life-cycle types in marine benthic invertebrates: Feeding larvae versus nonfeeding larvae versus direct development, Yoh Iwasa; Yoichi Yusa; Sachi Yamaguchi, Many marine invertebrates have a benthic adult life with planktonic long feeding larval stages (planktotrophy). In other species, planktonic larvae do not eat, and after a rather short period, they settle and initiate their benthic stages (lecithotrophy). Still other species skip planktonic larval stages altogether, and adults produce benthic offspring (direct development). In this paper, we develop an evolutionary game among different life-cycle types and examine the conditions for each life-cycle type to win in a seasonal environment. The growth rate and mortality of benthic individuals are the same among all three life-cycle types, the local habitat (patches) for benthic individuals have a finite longevity, and adults may engage in a limited dispersal just before breeding. Planktotrophy evolves if the planktonic stages are more efficient in terms of biomass gain than benthic life. Otherwise, lecithotrophy or direct development should evolve. Among them, direct development is more advantageous than lecithotrophy if the cost of having planktonic larvae is large, the habitat for benthic individuals is stable, and adults engage in some dispersal., Jan. 2022, 537, 111019, 111019, Scientific journal, True
  • Refereed, Organisms Diversity & Evolution, Phylogeny and evolution of functional chloroplast retention in sacoglossan sea slugs (Gastropoda: Heterobranchia), Yu Hirokane; Ayaka Miyamoto; Jun Kitaura; Rie Nakano; Yayoi M. Hirano; Masako Kawane; Yoichi Yusa, Nov. 2021, 1, 11, Scientific journal
  • Refereed, Journal of Theoretical Biology, Elsevier BV, Evolution of life cycle dimorphism: An example of sacoglossan sea slugs, Sachi Yamaguchi; Yoichi Yusa; Yoh Iwasa, Sep. 2021, 525, 110760, 110760, Scientific journal
  • Refereed, Molluscan Research, Extremely short embryonic period of the intertidal pulmonate limpet Siphonaria sirius (Pilsbry, 1895), Yoko Wada; Yoichi Yusa, Jun. 2021, 41, 3, 235, 242, Scientific journal
  • Refereed, 南紀生物, 潮下帯上部におけるハナデンシャ(ドーリス下目:フジタウミウシ科)幼体の初記録, 上原春香; 中野理枝; 遊佐陽一, Jun. 2021
  • Refereed, Applied Entomology and Zoology, Predation by the carrion crow Corvus corone (Passeriformes: Corvidae) on the apple snail Pomacea canaliculata (Architaenioglossa: Ampullariidae) in different locations in Japan, Haruka Uehara; Hiroshi Murakami; Yoichi Yusa, May 2021, 56, 385, 392, Scientific journal
  • Refereed, 関西病虫害研究会報, スクミリンゴガイのトラップ用誘引資材の圃場における評価, 吉田和弘; 鈴木絵美子; 遊佐陽一, May 2021, 63, 151, 154, Scientific journal
  • Refereed, Current Biology, Elsevier BV, Extreme autotomy and whole-body regeneration in photosynthetic sea slugs, Sayaka Mitoh; Yoichi Yusa, Mar. 2021, 31, 5, R233, R234, Scientific journal
  • Refereed, Oecologia, Adaptive significance of light and food for a kleptoplastic sea slug: implications for photosynthesis, H Shiroyama; S Mitoh; TY Ida; Y Yusa, Oct. 2020, 194, 455, 463
  • Refereed, Journal of Experimental Marine Biology and Ecology, Seasonal utilization patterns of two snail hosts by the epizoic limpet Lottia tenuisculpta (Gastropoda: Patellogastropoda), R Nakayama; T Nakano; Y Yusa, Oct. 2020, 530, 151402
  • Refereed, Journal of Crustacean Biology, Life cycles of the rhizocephalan Boschmaella japonica Deichmann & Høeg, 1990 (Cirripedia: Chthamalophilidae) and its host barnacle Chthamalus challengeri Hoek, 1883 (Cirripedia: Chthamalidae), M Yabuta; JT Høeg; S Yamato; Y Yusa, Jun. 2020
  • Refereed, Molecular biology reports, Microsatellite DNA markers applicable to paternity inference in the androdioecious gooseneck barnacle Octolasmis warwickii (Lepadiformes: Poecilasmatidae), M Kobayashi; Y Yusa; M Sekino, May 2020, 47, 4885, 4890
  • Ecology and Evolution, Different effects of mating group size as male and as female on sex allocation in a simultaneous hermaphrodite, MM Tamechika; K Matsuno; S Wada; Y Yusa, Feb. 2020, 10, 5, 2492, 2498
  • Journal of Molluscan Studies, Effect of inbreeding on sex ratio in the apple snail Pomacea canaliculata, N Kumagai; Y Yusa, Aug. 2019, 85, 3, 348, 353
  • Transitions between sexual systems, Hermaphrodites, dwarf males, and females: evolutionary transitions of sexual systems in barnacles, Y Yusa, Mar. 2019, 221, 245
  • Not Refereed, Ecological Indicators, Elsevier B.V., Effects of temperature and red tides on sea urchin abundance and species richness over 45 years in southern Japan, Shun-Ichi Ohgaki; Tetsuya Kato; Naomasa Kobayashi; Hidetomo Tanase; Naoki H. Kumagai; So Ishida; Tomoyuki Nakano; Yoko Wada; Yoichi Yusa, Continuous long-term monitoring is important for detecting ecological changes and understanding their causes, including anthropogenic impacts such as climate changes and eutrophication. Nonetheless, such long-term population studies have been rare, especially for sea urchins, which can affect community dynamics owing to their extensive herbivory and large population fluctuations. Here we present a long-term (from 1963 to 2014) dynamics of sea urchins in a fixed quadrat on a lower intertidal rocky flat in Hatakejima Island, southern Japan. We also conducted a complementary survey over the entire island approximately every five years from 1975 to 2013, and a 41-year assay for developmental abnormality of the sea urchin Heliocidaris crassispina using water adjacent to the island. The abundance of three commonest species in this area (H. crassispina, Echinostrephus molaris, and Echinometra spp.) and the richness of urchin species showed large variations, with high numbers in the 1960s and 1970s, followed by an abrupt decline in the late 1970s or early 1980s, and a gradual recovery subsequently. The species abundance and richness in the entire island survey showed good correlations with those in the quadrat census. Statistical analyses indicated that increasing water temperature and red tides were the major factors influencing the dynamics of abundance and species richness. Our studies reveal that anthropogenic environmental changes influence the long-term dynamics in abundance and richness of sea urchins., Jan. 2019, 96, 1, 684, 693, Scientific journal
  • Not Refereed, ZOOLOGICAL STUDIES, BIODIVERSITY RESEARCH CENTER, ACAD SINICA, Direct Growth Measurements of Two Deep-sea Scalpellid Barnacles, Scalpellum stearnsii and Graviscalpellum pedunculatum, Yoichi Yusa; Natsumi Yasuda; Tomoko Yamamoto; Hiromi Kayama Watanabe; Takuo Higashiji; Atsushi Kaneko; Kazuki Nishida; Jens T. Hoeg, Yoichi Yusa, Natsumi Yasuda, Tomoko Yamamoto, Hiromi Kayama Watanabe, Takuo Higashiji, Atsushi Kaneko, Kazuki Nishida, and Jens T. Hoeg (2018) Little is known about the growth rates of invertebrates living in ordinary deep-sea habitats such as continental slopes. Thus, the growth rates of two species of the deep-sea scalpellid barnacles, Scalpellum stearnsii and Graviscalpellum pedunculatum, were studied in two aquaria (at Nara and Okinawa Churaumi, Japan). In addition, growth of an S. stearnsii individual after 1 year of deployment was measured in the field Overall, adult individuals of both species showed slow growths over 8 months (at Nara) and 2 years (at Okinawa) of rearing (e.g., at Nara:2.0 +/- 3.6 mu m d(-1) for S. stearnsii and 5.9 +/- 2.7 mu m d(-1) for G. pedunculatum; mean +/- SD). In contrast, growth rates of juvenile S. steamsii at Nara were greater (15 +/- 7.7 mu m d(-1)). The in situ growth rate of the adult S. stearnsii (3.4 mu m d(-1)) was greater than the average, but within the range of the rates of similar-sized individuals recorded in aquaria. Compared with other pedunculate barnacles, both species show small growth rates typical for deep-sea animals., Jun. 2018, 57, article 29, Scientific journal
  • Not Refereed, GENETICA, SPRINGER, Evidence of oligogenic sex determination in the apple snail Pomacea canaliculata, Yoichi Yusa; Natsumi Kumagai, A small number of genes may interact to determine sex, but few such examples have been demonstrated in animals, especially through comprehensive mating experiments. The highly invasive apple snail Pomacea canaliculata is gonochoristic and shows a large variation in brood sex ratio, and the involvement of multiple genes has been suggested for this phenomenon. We conducted mating experiments to determine whether their sex determination involves a few or many genes (i.e., oligogenic or polygenic sex determination, respectively). Full-sib females or males that were born from the same parents were mated to an adult of the opposite sex, and the brood sex ratios of the parents and their offspring were investigated. Analysis of a total of 4288 offspring showed that the sex ratios of offspring from the full-sib females were variable but clustered into only a few values. Similar patterns were observed for the full-sib males, although the effect was less clear because fewer offspring were used (n = 747). Notably, the offspring sex ratios of all full-sib females in some families were nearly 0.5 (proportion of males) with little variation. These results indicate that the number of genotypes of the full-sibs, and hence genes involved in sex determination, is small in this snail. Such oligogenic systems may be a major sex-determining system among animals, especially those with variable sex ratios., Jun. 2018, 146, 3, 265, 275, Scientific journal
  • Not Refereed, Organisms Diversity and Evolution, Springer Verlag, When dwarf males and hermaphrodites copulate: first record of mating behaviour in a dwarf male using the androdioecious barnacle Scalpellum scalpellum (Crustacea: Cirripedia: Thoracica), Niklas Dreyer; Jens T. Høeg; Martin Heß; Stefan Sørensen; Uwe Spremberg; Yoichi Yusa, Mating behaviour between a dwarf male and its hermaphrodite partner was observed for the first time in cirripedes using the androdioecious barnacle Scalpellum scalpellum. Mating between hermaphrodites was also observed. The dwarf males are located on the rim of the mantle cavity of the hermaphrodite partner. When mating, the male extends the penis, which is four times longer than its body. The penis first assumes a straight stance where it is waved around in a searching mode. Upon touching the cirri of the hermaphrodite, the penis and the cirri engage in prolonged contact during which hermaphrodite feeding is suspended. Thereafter the penis assumes a U-bend to reach into the brood chamber, where after the mantle valves are closed tightly around the penis. The nearly transparent penis is a tube of very thin cuticle, equipped with pairs of side branches but not containing any visible tissue. The penis enables the minute male, situated outside the brood chamber, to securely deposit sperm into its partner. Adjacently situated hermaphrodites interact socially in between feeding sessions by reorienting themselves on the peduncle to touch each other with their cirri. This can be followed by precopulatory behaviour, where one or both individuals extend the penis to touch their partner, leading again to actual copulation where the penis of one individual is inserted into the other. We discuss the results in the context of the diverse reproductive strategies found in cirripede barnacles., 01 Mar. 2018, 18, 1, 115, 123, Scientific journal
  • Not Refereed, Venus, Development of 11 microsatellite markers and paternity analysis in the invasive apple snail Pomacea canaliculata, 遊佐 陽一; Yamamoto, S; Komasu, H; Kitaura, J; Aoyama, T; Iwaguchi, S; Nakamura, M; Kawane, M; Collins, T. M; Yusa, Y, 2018, 76, 79, 85
  • Not Refereed, Zoological Journal of the Linnean Society, In the footsteps of Darwin: Morphology, ontogeny and adaptive evolution of dwarf male attachment sites in scalpellid barnacles (Crustacea: Cirripedia: Thoracica) - implications for phylogeny and the evolution of sexual systems, 遊佐 陽一; Dreyer, N; Yusa, Y; Gale, A; Melzer, R. R; Yamato, S; Høeg, J. T, 2018, 184, 4, 999, 1023
  • Not Refereed, Biological Journal of the Linnean Society, Sex allocation and maintenance of androdioecy in the pedunculated barnacle Scalpellum scalpellum (Crustacea: Cirripedia: Thoracica), 遊佐 陽一; Dreyer, N; Sørensen, S; Yusa, Y; Sawada, K; Nash, D. R; Svennevig, N; Høeg, J. T, 2018, 124, 4, 776, 788
  • Not Refereed, MARINE BIOLOGY, SPRINGER HEIDELBERG, Effects of a crustacean parasite and hyperparasite on the Japanese spiny oyster Saccostrea kegaki, Noriko Yasuoka; Yoichi Yusa, Parasitism is one of the most common interspecific interactions, but little information exists on the detailed relationships among hosts, parasites, and hyper-parasites (secondary parasites) in marine ecosystems. Pea crabs parasitize a wide variety of marine animals, and the crabs themselves are often parasitized by other animals. The present study investigated the relationships among the oyster Saccostrea kegaki, its parasite, the pea crab Pinnotheres boninensis, and a hyperparasite, the isopod Onychocepon resupinum. Field sampling was conducted during the oyster's reproductive season (June-September 2014 and 2015) to evaluate effects of the pea crab on the body weight, maturation, and sex of the oyster in western Japan (Banshozaki, Shirahama Town, Wakayama Pref.; 33.41 degrees N, 135.20 degrees E). The relationship between the pea crab and the isopod and indirect effects of the isopod on the oyster were also investigated. The pea crab reduced the oyster's body weight and affected its reproduction: the proportion of mature individuals was lower in infested oysters (39.1%) than in non-infested ones (86.2%). The isopod affected the crab's sexual characteristics: infested female crabs had poorly developed ovaries, and infested males showed degrees of feminization and increased body size. The prevalence of the isopod was much higher in male (47.1%) than female (6.4%) crabs inside the oyster shells, suggesting that the parasitized male crabs became larger and were forced to remain inside the shells. Therefore, the isopod appears to have an indirect negative impact on the oyster by changing the male crab's traits., Nov. 2017, 164, 11, Article 217, Scientific journal
  • Not Refereed, ECOLOGY, WILEY, Roles of the seasonal dynamics of ecosystem components in fluctuating indirect interactions on a rocky shore, Yoko Wada; Keiji Iwasaki; Takashi Y. Ida; Yoichi Yusa, Accurately evaluating the strengths of direct (i. e., consumptive and non-consumptive) effects and indirect (density-and trait-mediated) interactions is crucial for understanding the mechanisms of the maintenance and dynamics of an ecosystem. However, an in situ evaluation has not been conducted for a long enough period of time to fully consider the seasonality and life histories of the community components. We conducted a 9-month (from summer to spring) field experiment in an intertidal rocky shore ecosystem involving the carnivorous snail, Thais clavigera, its prey, the limpet Siphonaria sirius, and their resources, the cyanobacterium (blue-green alga) Lithoderma sp. and the green algae Ulva spp. From summer to autumn, the predation pressure was high, and the consumptive and non-consumptive effects of the predator had opposite (positive and negative, respectively) effects on the prey. Both the density-and trait-mediated indirect interactions decreased the coverage of Lithoderma and increased the coverage of Ulva. As the predation pressure decreased in autumn, the predator affected both the adults and the new recruits of the prey. The trait-mediated interactions still existed, but the density-mediated interactions were not detected. From winter to spring, no direct effects or indirect interactions were detected because of the low predation pressure. Our investigation highlights previously unnoticed processes-showing that the strengths of the direct effects and indirect interactions fluctuate greatly with the seasonality of the ecosystem components., Apr. 2017, 98, 4, 1093, 1103, Scientific journal
  • Not Refereed, Plankton and Benthos Research, Plankton Society of Japan, Direct evidence of bi-directional sex change in natural populations of the oysters Saccostrea kegaki and S. Mordax, Noriko Yasuoka; Yoichi Yusa, Two Saccostrea oysters (S. glomerata and S. cucullata) are considered to be protandric hermaphrodites based on indirect observations. However, no other information is available on the sexual systems of Saccostrea oysters and the potential for bidirectional sex change has not previously been reported in them. Therefore, the present study was undertaken to investigate the sexual systems of S. kegaki and S. mordax in western Japan, utilizing field sampling and in situ experiments. In the field sampling, shell length (SL) and sex were determined during the reproductive season of these oysters (June–October) in 2012. Then, sex change was directly observed between 2013 and 2016 by determining the sex of individuals through gonadal biopsy, re-attaching the individuals in the field, collecting the survivors in the following year, and determining their sex by dissection. In both species, the proportion of males decreased with increasing SL, although the SL of males and females greatly overlapped. Direct observations showed that both male-to-female and female-to-male sex change occurred. Thus, our results indicated that both Saccostrea species tend to be protandric, but have the ability to change sex in both directions under natural conditions., 2017, 12, 1, 78, 81
  • Not Refereed, CRUSTACEANA, BRILL ACADEMIC PUBLISHERS, LARVAL DEVELOPMENT OF THE EPIZOIC BARNACLE OCTOLASMIS UNGUISIFORMIS KOBAYASHI & KATO, 2003 (CIRRIPEDIA, PEDUNCULATA), H. Wijayanti; Y. Yusa; R. Kado, Larvae of the androdioecious and endangered barnacle, Octolasmis unguisiformis, were cultured in the laboratory for the first time. The larvae passed through six free-swimming naupliar stages and a cyprid stage. The naupliar stages required a combined minimum of 44 days at 25 degrees C, and the cyprid stage lasted up to 7 days. However, none of the cyprids settled, even if the host crab (Macrophthalmus milloti) was introduced. The morphological features of the naupliar stages are described and compared with other Octolasmis spp., 2017, 90, 3, 321, 336, Scientific journal
  • Not Refereed, Sessile Organisms, THE SESSILE ORGANISMS SOCIETY OF JAPAN, Diversity of sexual expressions in barnacles, Yusa Yoichi, As first discovered by Darwin, barnacles (Cirripedia: Thoracica) show diverse sexual systems including simultaneous hermaphroditism, dioecy (separate sexes), and androdioecy (coexistence of males and hermaphrodites). The males are always much smaller than their hermaphrodite or female mates (hence called dwarf males). Here I review recent theoretical and empirical studies that address causes of the diverse sexual systems in barnacles. The size of mating groups (or more accurately, the average number of matings from other hermaphrodites a female-acting hermaphrodite is expected to accept) is identified as the most important environmental factor responsible for the evolutionary transitions of sexual systems in barnacles. I suggest that barnacles offer both theoretical and empirical model systems for understanding the evolution of sexual systems in animals., 2017, 34, 1, 13, 18
  • Not Refereed, JOURNAL OF MOLLUSCAN STUDIES, OXFORD UNIV PRESS, Effects of size and gregariousness on individual sex in a natural population of the Pacific oyster Crassostrea gigas, Noriko Yasuoka; Yoichi Yusa, Crassostrea oysters show intraspecific variation in sexuality, including dioecy as well as sequential and simultaneous hermaphroditism, but their sexuality under natural conditions has rarely been reported. We examined sexuality and the effects of body size and gregariousness on sexuality in a natural population of the Pacific oyster C. gigas in southern Japan. First, monthly samplings were made during their reproductive season (May -August 2012) to study the sex of wild individuals. The proportion of males was found to decrease with increasing shell length (SL) and was greater in gregarious than solitary individuals. Simultaneous hermaphrodites were encountered infrequently (c. 1%). The negative relationship between the proportion of males and SL was also observed among the new cohort that had settled within one year. Next, we directly observed sex change by inspecting the sex of the same individuals through biopsy in two consecutive years (2013-2014; long-term experiment) or within a reproductive season (May-August 2014; short-term experiment) in the same population. Manipulation of the gregariousness (whether solitary or gregarious) was also conducted at the beginning of the experiments. When the individuals were re-collected, sex change in both directions was observed both in the long- and short-term experiments. Moreover, sex change from male to female was promoted when individuals were made solitary rather than gregarious. In summary, our study has shown that C. gigas has a tendency for protandry and has the ability to change sex in both directions under natural conditions in an area where they are native. Although within-season sex change of Crassostrea species has heretofore been unknown, C. gigas can change sex even in the short term. We suggest that such plasticity and the resulting diverse sexuality may be adaptive for sessile organisms such as oysters., Nov. 2016, 82, 485, 491, Scientific journal
  • Not Refereed, JOURNAL OF MOLLUSCAN STUDIES, OXFORD UNIV PRESS, Survival, growth and reproduction of the invasive apple snail Pomacea canaliculata in an irrigation canal in southern Japan, Kazuhiro Yoshida; Yoichi Yusa; Yoko Yamanishi; Keiichiro Matsukura; Takashi Wada, Nov. 2016, 82, 600, 602
  • Not Refereed, BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, WILEY-BLACKWELL, Sex determination in the androdioecious barnacle Scalpellum scalpellum (Crustacea: Cirripedia), Jens T. Hoeg; Yoichi Yusa; Niklas Dreyer, How androdioecy (coexistence of hermaphrodites and males) is maintained is still poorly understood. Therefore, sex determination was studied in the androdioecious barnacle Scalpellum scalpellum L. First, 247 cypris larvae from seven broods were investigated for sexual dimorphism in larval morphology and found to be all identical. Second, experiments with cyprids showed that males and hermaphrodites differ distinctly in morphology as soon as 4-5days after settlement. Third, 14252 cyprids were allowed to settle on the bottom of their culture cages, and all surviving larvae developed into hermaphrodites and none into dwarf males. Fourth, larvae settled in hermaphrodite receptacles (i.e. future males) were removed at increasing intervals after settlement to study if the male and hermaphrodite sexual expressions are fixed or plastic. All larvae became dwarf males if allowed to stay there for more than 8h after settlement. But if removed within 3h after settlement, half of them developed into hermaphrodites. We conclude that an environmental sex determination mechanism operates in S.scalpellum. Together with a 1:1 hermaphrodite/male ratio observed in previously reported experiments offering a free choice of settlement, we suggest that all larvae are potential hermaphrodites, but only 50% can settle in hermaphrodite receptacles and yield males., Jun. 2016, 118, 2, 359, 368, Scientific journal
  • Not Refereed, BIOLOGICAL BULLETIN, UNIV CHICAGO PRESS, Plastic Sexual Expression in the Androdioecious Barnacle Octolasmis warwickii (Cirripedia: Pedunculata), Hendry Wijayanti; Yoichi Yusa, Most barnacles are simultaneous hermaphrodites, but dwarf males are also found attached to hermaphrodites in several species. This biologically rare phenomenon of the coexistence of males and hermaphrodites is termed androdioecy. To test whether the hermaphrodite and male sexes are fixed or plastic in the androdioecious pedunculate barnacle Octolasmis warwickii, we conducted a series of 22-day-long transplanting experiments to evaluate the effects of a) the original site (attached to the conspecific vs. attached directly to the substrate) and b) the transplanting site (conspecific-attached vs. substrate-attached). Penis length (as an index of male function), the presence or absence of egg mass (female function), and growth rate were investigated. As with natural dwarf males, individuals that were transplanted onto conspecifics developed longer penises than did those that were transplanted onto the substrate. The original site of attachment also affected penis length. However, no significant effects of the original site or the transplanting were detected in egg-laying activities, as only one experimental individual laid eggs. Individuals that were transplanted onto conspecifics grew less than those that were attached to the substrate. These results indicate that individual sexual expression is affected by the environment in O. warwickii., Feb. 2016, 230, 1, 51, 55, Scientific journal
  • Not Refereed, DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS, PERGAMON-ELSEVIER SCIENCE LTD, Effects of food availability on growth and reproduction of the deep-sea pedunculate barnacle Heteralepas canci, Natsumi Yasuda; Norio Miyamoto; Yoshihiro Fujiwara; Tomoko Yamamoto; Yoichi Yusa, Sessile animals living on continental shelves or slopes may adjust their growth and reproduction according to temporally and spatially variable food availability, but little information is available on these animals to date. We collected the pedunculate barnacle Heteralepas canci on a continental slope at a depth of 229 m off Cape Nomamisaki in southern Japan. We developed a rearing method for the barnacles and studied their growth and reproduction at different food levels in the laboratory. A total of 136 individual H. canci were fed with Artemia saline larvae and brewer's yeast at three different food levels for 100 days. Both the growth and the ovary development were delayed when food availability was low, whereas the survival rate was lower at the high food level. In addition, an individual survived under complete starvation for 167 days. We concluded that H. canci has plastic life history traits that are adaptive for variable food availability. (C) 2015 Elsevier Ltd. All rights reserved., Feb. 2016, 108, 53, 57, Scientific journal
  • Not Refereed, ZOOLOGICAL STUDIES, BIODIVERSITY RESEARCH CENTER, ACAD SINICA, Host Relation, Size and Reproduction in the Burrowing Barnacle Trypetesa lampas (Hancock) (Crustacea Cirripedia Acrothoracica), Sofie K. D. Nielsen; Jens T. Hoeg; Yoichi Yusa, The aim of this study is to investigate the population biology of the burrowing barnacle Trypetesa lampas, a symbiont of hermit crabs and representing the little known cirripede group Acrothoracica. We put special emphasis on the host-barnacle relation and reproduction. A total of 341 hermit crabs from the west coast of Sweden was captured in November 2009 and August 2010, and examined for the associated burrowing barnacles. We found a mean load of 1.4 T. lampas per host and an average prevalence of 31.4% with no seasonal variation. Male hermit crabs also carried T. lampas, indicating that T. lampas does not rely on egg-predation to any substantial degree. The T. lampas load was positively related to host size, but otherwise their frequency distribution did not differ from random. The position of the burrow in the columella of the shell was positively associated with T. lampas size. Reproduction seems to occur throughout the year. We found ovigerous females also in winter, although less frequently than in summer, and no difference in the number of dwarf males between the summer and winter samples. The data from the present study site deviates in many respects (prevalence, female and male load, reproductive cycle, host relation) from previous studies on this and closely related acrothoracican species. This emphasizes that a basic lack of knowledge still exists concerning most aspects of acrothoracican reproduction, life cycles and host relation., 2016, 55, 14, 1, 10, Scientific journal
  • Not Refereed, MALACOLOGIA, INST MALACOL, VARIATION IN THE SEX RATIO OF APPLE SNAILS (POMACEA SPP.) IN THEIR NATIVE RANGE, Yoichi Yusa; Jun Kitaura; Nestor J. Cazzaniga, The brood sex ratio of the apple snail Pomacea canaliculata is highly variable among parents in areas where it has been introduced. Such variation in the sex ratio may reflect variation in the source population, or it may have stemmed from the mixture of multiple source populations with different sex-determining mechanisms. To distinguish these hypotheses, the sex ratios of F-1 (hatchlings from wild-collected egg masses) and F-2 snails (produced from crosses of the F-1 snails) from three sites in the native range in Argentina were studied. The sex ratios of the F-1 snails were not significantly different from 0.5, although there was a slight but significant difference among populations. The F-2 broods from intra-population crosses also lacked variation in the sex ratio. However, the sex ratios in F-2 broods from inter-population crosses were highly variable, from 0 (all females) to 0.84 (mostly males). Thus, the large variation in the sex ratio in areas where P. canaliculata has been introduced is probably due to the mixture of source populations., 2016, 59, 2, 239, 245, Scientific journal
  • Not Refereed, MOLECULAR PHYLOGENETICS AND EVOLUTION, ACADEMIC PRESS INC ELSEVIER SCIENCE, The origins and evolution of dwarf males and habitat use in thoracican barnacles, Hsiu-Chin Lin; Jens T. Hoeg; Yoichi Yusa; Benny K. K. Chan, Barnacles are exceptional in having various sexual systems (androdioecy, hermaphroditism, dioecy) and with a high morphological diversity of males, though these are always minute (dwarf) compared to their female or hermaphrodite partners. For the first time, we use a multiple DNA marker-based phylogeny to elucidate the ancestral states and evolution of (1) dwarf males, (2) their morphology when present, (3) their attachment site on the partner, and (4) habitat use in thoracican barnacles. Our taxon sampling was especially rich in rare deep-sea Scalpelliformes and comprised species with diverse sexual systems and dwarf male morphologies. Within the thoracican barnacles dwarf male evolution is subject to extensive convergence, but always correlated to similar ecological conditions. Males evolved convergently at least four times from purely hermaphroditic ancestors, in each case correlated with the invasion into habitats with low mating group sizes. The independent evolution of dwarf males in these lineages dovetails with the males having different morphologies and occurring in several different locations on their sexual partner. (C) 2015 Elsevier Inc. All rights reserved., Oct. 2015, 91, 1, 11, Scientific journal
  • Not Refereed, JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY, ELSEVIER SCIENCE BV, Prey density affects strengths of density- and trait-mediated indirect interactions of predators on an algal community, Yoko Wada; Keiji Iwasaki; Yoichi Yusa, In trophic cascades, predators can indirectly affect resources by reducing prey density (density-mediated indirect interactions; DMIIs) or by changing prey traits, such as their behavior, morphology, physiology, or life history (trait-mediated indirect interactions; TMIIs). Although the importance of predator (e.g., foraging strategy) and resource characteristics (e.g., quantity) in these indirect interactions is well recognized, little attention has been paid to prey characteristics (e.g., density), especially in field studies. We focused on a marine trophic cascade involving the carnivorous snail Thais clavigera, its limpet prey Siphonaria sirius, and the algae Lithoderma sp. and Ulva sp. Using intertidal rocks as natural replicates, we experimentally evaluated the in situ effects of the DMIIs and TMIIs on the algal community under two density ranges of prey. The strengths of consumptive effects (CEs) and non-consumptive effects (NCEs) of the predator on the prey limpet were also monitored to elucidate the mechanisms of the indirect interactions. At high densities, CEs decreased the percentage of individual limpets that disappeared (that likely died); however, neither DMIIs nor TMIIs were detected. At low densities, both CEs and NCEs reduced the per capita feeding rate and CEs reduced the growth rate of limpets. Moreover, Lithoderma sp. was replaced by Ulva sp. through both DMIIs and TMIIs. These results suggest that prey density is a key determinant of the strengths of CEs and NCEs, and notably, of DMIIs and TMIIs. (C) 2015 Elsevier B.V. All rights reserved., Jul. 2015, 468, 67, 73, Scientific journal
  • Not Refereed, INVERTEBRATE BIOLOGY, WILEY-BLACKWELL, Dwarf males in the epizoic barnacle Octolasmis unguisiformis and their implications for sexual system evolution, Kota Sawada; Ryuta Yoshida; Keiko Yasuda; Sachi Yamaguchi; Yoichi Yusa, Descriptions of the diversity of sexual systems in animal taxa such as the thoracican barnacles are needed to study the evolution of sexual systems. Androdioecious systems (coexistence of hermaphrodites and males) are particularly important due to their possible role as evolutionary intermediates in transitions between hermaphroditism and dioecy. In this study, we used histology to examine the sexual system of the crab-epizoic barnacle Octolasmis unguisiformis to determine if dwarf males were present or not; a previous study reported the existence of conspecific-attached individuals, but did not investigate their sexuality. All conspecific-attached individuals were dwarf males, irrespective of their attachment site. However, crab-attached individuals never acted as dwarf males even if they were small and lived together with large individuals. The result emphasizes the importance of attachment to conspecifics, but not to specific sites on conspecifics, in the evolution of dwarf males. Other individuals were hermaphroditic, indicating androdioecy in this species. However, their functional sexuality (that is, whether they actually do act as males) requires further study. The presence of dwarf males in this species supports theoretical predictions that small group size, short-lived habitats, or spatial limitation favor the evolution of dwarf males., Jun. 2015, 134, 2, 162, 167, Scientific journal
  • Not Refereed, MARINE BIOLOGY, SPRINGER HEIDELBERG, Phototaxis of sacoglossan sea slugs with different photosynthetic abilities: a test of the 'crawling leaves' hypothesis, Ayaka Miyamoto; Atsushi Sakai; Rie Nakano; Yoichi Yusa, Several sacoglossan sea slugs utilise chloroplasts ingested from algae for photosynthesis (kleptoplasty), a unique trophic strategy unknown in other animals. Its adaptive significance, especially the behavioural adaptations involved in this phenomenon, has not been fully explored. To address this issue, the effects of kleptoplasty on phototaxis were investigated, both across and within species, using sacoglossans collected along Japanese coasts in 2012 and 2013. First, the presence of phototaxis and preferred light intensity was studied in five sacoglossans with various photosynthetic capabilities using an I-maze with a light gradient (4-330 mu mol photons m(-2) s(-1)). Each individual was allowed to move for 30 min to choose the optimal light intensity. Elysia hamatanii, E. trisinuata, and Plakobranchus ocellatus, all with high photosynthetic activity (i.e. kleptoplastic), showed positive phototaxis. Among them, E. hamatanii preferred the highest light intensity followed by P. ocellatus and E. trisinuata, and the order corresponded with the shallowness of their habitats. Conversely, Stiliger ornatus and Placida sp., with virtually no photosynthetic activity (non-kleptoplastic), showed neutral and negative phototaxis, respectively. Next, the phototaxis of E. hamatanii individuals with (fed) and without (starved) functional chloroplasts was compared to examine the effects of the presence of kleptoplasts on phototaxis within a species. Both fed and starved individuals showed positive phototaxis, but the preferred light intensity of starved individuals was lower than that of fed individuals. These results suggest that sacoglossans with functional chloroplasts exhibit positive phototaxis towards a preferred light intensity which may benefit photosynthesis efficiency., Jun. 2015, 162, 6, 1343, 1349, Scientific journal
  • Not Refereed, MALACOLOGIA, INST MALACOL, INSIGHTS FROM AN INTEGRATED VIEW OF THE BIOLOGY OF APPLE SNAILS (CAENOGASTROPODA: AMPULLARIIDAE), Kenneth A. Hayes; Romi L. Burks; Alfredo Castro-Vazquez; Philip C. Darby; Horacio Heras; Pablo R. Martin; Jian-Wen Qiu; Silvana C. Thiengo; Israel A. Vega; Takashi Wada; Yoichi Yusa; Silvana Burela; M. Pilar Cadierno; Juan A. Cueto; Federico A. Dellagnola; Marcos S. Dreon; M. Victoria Frassa; Maximiliano Giraud-Billoud; Martin S. Godoy; Santiago Ituarte; Eduardo Koch; Keiichiro Matsukura; M. Yanina Pasquevich; Cristian Rodriguez; Lucia Saveanu; Maria E. Seuffert; Ellen E. Strong; Jin Sun; Nicolas E. Tamburi; Maria J. Tiecher; Richard L. Turner; Patricia L. Valentine-Darby; Robert H. Cowie, Apple snails (Ampullariidae) are among the largest and most ecologically important freshwater snails. The introduction of multiple species has reinvigorated the field and spurred a burgeoning body of research since the early 1990s, particularly regarding two species introduced to Asian wetlands and elsewhere, where they have become serious agricultural pests. This review places these recent advances in the context of previous work, across diverse fields ranging from phylogenetics and biogeography through ecology and developmental biology, and the more applied areas of environmental health and human disease. The review does not deal with the role of ampullariids as pests, nor their control and management, as this has been substantially reviewed elsewhere. Despite this large and diverse body of research, significant gaps in knowledge of these important snails remain, particularly in a comparative framework. The great majority of the work to date concerns a single species, Pomacea canaliculata, which we see as having the potential to become a model organism in a wide range of fields. However, additional comparative data are essential for understanding this diverse and potentially informative group. With the rapid advances in genomic technologies, many questions, seemingly intractable two decades ago, can be addressed, and ampullariids will provide valuable insights to our understanding across diverse fields in integrative biology., Apr. 2015, 58, 1-2, 245, 302, Scientific journal
  • Not Refereed, JOURNAL OF MOLLUSCAN STUDIES, OXFORD UNIV PRESS, Antipredator behaviour in response to single or combined predator cues in the apple snail Pomacea canaliculata, Eriko Ueshima; Yoichi Yusa, The documentation of antipredator behaviour associated with different risk levels (threat-sensitive predator avoidance), different predators (predator-specific avoidance) or combined predators (multiple predator avoidance) in freshwater caenogastropods is limited. We studied the antipredator behaviour of predator-naive hatchlings of the invasive apple snail Pomacea canaliculata to chemical cues from the common carp (Cyprinus carpio), Reeve's turtle (Mauremys reevesii) and crushed conspecifics in three laboratory experiments. First, we tested the snails' responses of crawling out of the water and self-burial in the sand to odour from a single nonfeeding predator or crushed conspecifics. A greater proportion of snails responded to odour from crushed conspecifics than to turtle or carp odours. Second, we studied the snails' responses to cues simulating a single feeding predator. When combined with cues from crushed conspecifics, snails tended to bury themselves in the sand in response to the turtle odour whereas they tended to crawl above the waterline in response to the carp odour. Third, we compared the snails' responses to single or combined predator cues. In the presence of cues from crushed conspecifics, the snails' responses to the combined odours from turtle and carp were more similar to the responses associated with the carp odour than to those associated with the turtle odour. Overall, these experiments indicate that P. canaliculata hatchlings show fine-tuned innate antipredator behaviour., Feb. 2015, 81, 51, 57, Scientific journal
  • Not Refereed, BIOLOGICAL INVASIONS, SPRINGER, Canal type affects invasiveness of the apple snail Pomacea canaliculata through its effects on animal species richness and waterweed invasion, Akiko Hara; Kenji Hamasaki; Kazuhiro Yoshida; Yoichi Yusa, Loss of complex natural microhabitats due to human activity is a major cause of decreased biodiversity but its effects on biological invasion are not well understood. The effects of physical environmental factors, especially the type of agricultural canals, on the invasive freshwater snail Pomacea canaliculata were studied at 33 sites in the Chikugogawa River basin, Kyushu, Japan. Differences among sites in the local fauna and vegetation were also monitored. Structural equation modeling with a model selection procedure revealed that canals with a concrete lining had more snails. The effect was indirect in that the concrete lining reduced animal species richness and increased the invasive waterweed Egeria densa, which may serve as a refuge, protecting the snails from predation. A tethering experiment conducted simultaneously indicated high predation pressure on the snails: over 20% of the tethered snails were lost within a day. Thus, human impacts may increase biological invasion by reducing biotic resistance and increasing the risk of invasional meltdown., Jan. 2015, 17, 1, 63, 71, Scientific journal
  • Not Refereed, CRUSTACEANA, BRILL ACADEMIC PUBLISHERS, DWARF MALES IN THE BARNACLE ALEPAS PACIFICA PILSBRY, 1907 (THORACICA, LEPADIDAE), A SYMBIONT OF JELLYFISH, Y. Yusa; S. Yamato; M. Kawamura; S. Kubota, In the pedunculate barnacle Alepas pacifica Pilsbry, 1907, a symbiont of jellyfish, several small individuals were found attached to conspecifics rather than directly to the host. We investigated whether these individuals act as dwarf males, as is known in some other species of barnacles. The conspecific-attached individuals had longer penes than juvenile hermaphrodites of similar sizes attached directly to the jellyfish, although there was no other morphological difference between these two types of individuals. Only the largest conspecific-attached individual was ovigerous. We conclude that the conspecific-attached individuals are dwarf males, which develop the male function at a smaller size than hermaphrodites do, with a small possibility of becoming hermaphroditic. This is the first report of dwarf males, and hence of the coexistence of males and hermaphrodites (androdioecy), in the family Lepadidae. In addition, the record of A. pacifica attached to Nemopilema nomurai Kishinouye, 1922, is reported herein as new to science., 2015, 88, 3, 273, 282, Scientific journal
  • Not Refereed, MARINE BIOLOGY RESEARCH, TAYLOR & FRANCIS AS, Sexual system of a symbiotic pedunculate barnacle Poecilasma kaempferi (Cirripedia: Thoracica), Sachi Yamaguchi; Sachi Yoshida; Atsushi Kaneko; Kota Sawada; Keiko Yasuda; Yoichi Yusa, Jul. 2014, 10, 6, 635, 640, Scientific journal
  • Not Refereed, MARINE BIOLOGY, SPRINGER, Relative importance and interactive effects of photosynthesis and food in two solar-powered sea slugs, Ayana Akimoto; Yayoi M. Hirano; Atsushi Sakai; Yoichi Yusa, Sacoglossans use chloroplasts taken from algal food for photosynthesis (kleptoplasty), but the adaptive significance of this phenomenon remains unclear. Two con-generic sacoglossans (Elysia trisinuata and E. atroviridis) were collected in 2009-2011 from Shirahama (33.69A degrees N, 135.34A degrees E) and Mukaishima (34.37A degrees N, 133.22A degrees E), Japan, respectively. They were individually maintained for 16 days under four experimental conditions (combination of light/dark and with/without food), and their survival rate and relative (=final/initial) weights were measured. Both light and food had positive effects on the survival in E. trisinuata, whereas no positive effects of light or food on survival were detected in E. atroviridis. Both light and food had positive effects on relative weights in both species, but light had smaller effects than food. A significant interaction term between light and food was detected in E. trisinuata (but not in E. atroviridis) in that only the presence of both resulted in weight gains. This result suggests that E. trisinuata can obtain sufficient additional energy from photosynthesis for sustaining growth when fresh chloroplasts are continuously supplied from algal food. In addition, fluorescence yield measurements showed that unfed individuals of both E. trisinuata and E. atroviridis lost photosynthetic activity soon (< 4 and 4-8 days, respectively). In conclusion, photosynthesis may function to obtain supplementary nutrition for sustaining growth when food is available in sacoglossans with short-term functional kleptoplasty., May 2014, 161, 5, 1095, 1102, Scientific journal
  • Not Refereed, ECOLOGY, ECOLOGICAL SOC AMER, Changes in algal community structure via density- and trait-mediated indirect interactions in a marine ecosystem, Yoko Wada; Keiji Iwasaki; Yoichi Yusa, In various terrestrial and aquatic ecosystems, predators affect resources indirectly via intermediate prey. Such indirect interactions involve reducing the density of the prey (density-mediated indirect interactions, DMIIs) or changing the behavioral, morphological, or life history traits of the prey (trait-mediated indirect interactions, TMIIs). Although the importance of TMIIs has been highlighted recently, the strengths of both DMIIs and TMIIs under natural conditions have rarely been evaluated, especially in the context of resource community structure. We studied a three-level marine food chain involving the carnivorous snail Thais clavigera, its limpet prey Siphonaria sirius, and the limpet's food sources, the algae Lithoderma sp. and Ulva sp. We measured the strengths of DMIIs and TMIIs and observed how the algal community changes under the pressure of natural predation by T. clavigera on S. sirius. Neither DMIIs nor TMIIs affected the total algal cover or chlorophyll content per unit area. However, both types of indirect interactions caused similar changes in algal composition by increasing the cover of Ulva and decreasing the cover of Lithoderma. This change in the algal community was caused by a reduction in the limpet's preferential consumption of the competitively dominant Ulva over Lithoderma. These results suggest that both DMIIs and TMIIs have similar effects on the changes in resource community structure under natural conditions., Nov. 2013, 94, 11, 2567, 2574, Scientific journal
  • Refereed, INTEGRATIVE AND COMPARATIVE BIOLOGY, OXFORD UNIV PRESS INC, Diverse, Continuous, and Plastic Sexual Systems in Barnacles, Yoichi Yusa; Mayuko Takemura; Kota Sawada; Sachi Yamaguchi, Barnacles (Crustacea: Thoracica) show diverse sexual systems, including simultaneous hermaphroditism, androdioecy (hermaphrodites + males), and dioecy (females + males). When males occur, they are always much smaller (called dwarf males) than conspecific hermaphrodites or females. Ever since Darwin made this discovery, many scientists have been fascinated by such diversity. In this study, we provide an overview of (1) the diversity of sexual systems in barnacles, (2) the continuity between different sexual systems in some genera or species, and (3) the plasticity in sexual expression in several species. First, although most barnacles are hermaphroditic, both theoretical and empirical studies suggest that females and dwarf males tend to occur in species with small mating groups. Low sperm competition among hermaphrodites and little chance to act as a male are both associated with small group sizes and identified as the forces promoting the evolution of dwarf males and pure females, respectively. Second, in some groups of barnacles, the distinction between hermaphrodites and dwarf males is unclear because of the potential of dwarf males to become hermaphrodites. As many barnacle species tend toward protandric simultaneous hermaphroditism (develop male function first and then add female function without discarding male function), the dwarf males in such cases are best described as potential hermaphrodites that arrest growth and emphasize male function much earlier because of attachment to conspecifics. This is presumably advantageous in fertilizing the eggs of the host individuals. The distinction between hermaphrodites and females may also be obscured in some species. Third, sex allocation and penial morphology are plastic in some species. We also report the results of a transplanting experiment on small individuals of the pedunculate barnacle Octolasmis angulata, which suggests that individuals transplanted onto conspecifics developed longer and broader penises than did control individuals. Overall, the diversity, continuity, and plasticity in the sexual systems of barnacles are sources of important insights into the evolution and maintenance of the diversity of sexual systems., Oct. 2013, 53, 4, 701, 712, Scientific journal
  • Not Refereed, FRESHWATER BIOLOGY, WILEY-BLACKWELL, Patterns of density dependence in growth, reproduction and survival in the invasive freshwater snail Pomacea canaliculata in Japanese rice fields, Kazuhiro Yoshida; Kazuo Hoshikawa; Takashi Wada; Yoichi Yusa, 1. Patterns of density dependence in growth, reproduction and survival are important for predicting the population dynamics of a species. The patterns may change with environmental factors, such as the harshness of winter, but very little is known about such patterns and their mechanisms in unmanipulated natural populations of invasive animal species. 2. We studied the extent of density dependence in the growth, reproduction and survival of an invasive freshwater snail, Pomacea canaliculata, in rice fields in Nara (cold district) and Kumamoto (warm district), Japan, over 2- and 1-year periods, respectively. 3. In both areas, growth was negatively density dependent within the same generation, and the density of snails in the parental generation negatively affected the growth of offspring. The number of eggs per unit area was independent of adult density, suggesting eggs per adult female were few at high densities. Survival over the cold winter of 2005-2006 was independent of density in Nara. However, survival over the warm winter of 2006-2007 in both Nara and Kumamoto was negatively density dependent. 4. Irrespective of the various negative density-dependent patterns, population density tended to show positive correlations with the density of the previous generation. This appears to reflect the substantial capacity of this snail to resist extremely low densities due to the various negative density-dependent patterns rather than indicating susceptibility to extinction at low densities., Oct. 2013, 58, 10, 2065, 2073, Scientific journal
  • Not Refereed, JOURNAL OF THEORETICAL BIOLOGY, ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, Dwarf males and hermaphrodites can coexist in marine sedentary species if the opportunity to become a dwarf male is limited, Sachi Yamaguchi; Kota Sawada; Yoichi Yusa; Yoh Iwasa, In many marine sedentary species, dwarf males coexist with large individuals who are either hermaphrodites or females. Simple models of the evolutionary game of sex allocation and life history choice predict that stable coexistence of dwarf males and hermaphrodites is rather difficult. In many of these models, however, newly settled larvae are assumed to choose freely between becoming a dwarf male or an immature fast growing individual. In this paper, we consider a new model in which the opportunity for a newly settled individual to become a dwarf male is limited, for example by the scarcity of large individuals near its settlement site. In the evolutionarily stable strategy, the stationary population is either (1) dominated by hermaphrodites, with dwarf males scarce or absent, if immature individuals are fast-growing, (2) a mixture of dwarf males and large females, if larval growth is slow and the opportunity to become dwarf males is high, (3) a mixture of dwarf males and hermaphrodites, if larval growth is slow and the opportunity to become dwarf males is limited. We also examine the case in which the opportunity to be a growing individual is spatially limited. (C) 2013 Elsevier Ltd. All rights reserved., Oct. 2013, 334, 101, 108, Scientific journal
  • Not Refereed, JOURNAL OF HEREDITY, OXFORD UNIV PRESS INC, Population Genetics of Sex Determination in Mytilus Mussels: Reanalyses and a Model, Yoichi Yusa; Sophie Breton; Walter R. Hoeh, Large variations in offspring sex ratio have been reported in Mytilus mussels, which show doubly uniparental inheritance of mitochondria (DUI). Here, we reanalyzed the published sex ratio data, using simple population genetics concepts and logistic regression. Contrary to previous studies that detected only maternal effects, we found both paternal and maternal effects on the offspring sex ratio. We propose that sex in Mytilus is controlled by a pair of nuclear sex ratio alleles expressed in the mother and by minor sex-determining genes inherited from the father and also possibly from the mother., May 2013, 104, 3, 380, 385, Scientific journal
  • Not Refereed, THEORETICAL POPULATION BIOLOGY, ACADEMIC PRESS INC ELSEVIER SCIENCE, Dwarf males, large hermaphrodites and females in marine species: A dynamic optimization model of sex allocation and growth, Sachi Yamaguchi; Kota Sawada; Yoichi Yusa; Yoh Iwasa, In this study, we investigate the evolutionarily stable schedule of growth and sex allocation for marine benthic species that contain dwarf males. We consider a population in an ephemeral microhabitat that receives a constant supply of larvae. Small individuals can immediately reproduce as a dwarf male or remain immature and grow. Large individuals allocate reproductive resources between male and female functions. The fraction c of newly settled individuals who remain immature and the sex allocation of large individuals m are quantities to evolve. In the stationary ESS, if the relative reproductive success of dwarf males is greater than the survivorship of immature individuals until they reach a mature size, then the population is a mixture of females and dwarf males. If the opposite inequality holds, the population is dominated by hermaphrodites and lacks dwarf males. There is no case in which a mixture of hermaphrodites and dwarf males to be the ESS in the stationary solution. The ESS can be solved by dynamic programming when the strategies depend on the age of the microhabitat (c (t) and m (t)). Typically, the ESS schedule begins with a population composed only of hermaphrodites, which is replaced by a mixture of dwarf males and hermaphrodites and then by a mixture of dwarf males and pure females. The relative importance of these three phases depends on multiple parameters. (c) 2013 Elsevier Inc. All rights reserved., May 2013, 85, 49, 57, Scientific journal
  • Not Refereed, JOURNAL OF THEORETICAL BIOLOGY, ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, Sexual systems and dwarf males in barnacles: Integrating life history and sex allocation theories, Sachi Yamaguchi; Yoichi Yusa; Kota Sawada; Satoshi Takahashi, Barnacles, which are sedentary marine crustaceans, have diverse sexual systems that include simultaneous hermaphroditism, androdioecy (coexistence of hermaphrodites and males) and dioecy (females and males). In dioecious and androdioecious species, the males are very small and are thus called dwarf males. These sexual systems are defined by two factors: sex allocation of non-dwarf individuals and the presence or absence of dwarf males. We constructed an ESS model treating sex allocation and life history simultaneously to explain sexual systems in barnacles. We analyzed the evolutionarily stable size-dependent resource allocation strategy to male reproductive function, female reproductive function and growth in non-dwarf barnacles, and the ESS proportion of dwarf males, under conditions of varying mortality and food availability. Sex allocation in non-dwarf individuals (hermaphrodites or females) is affected by mate availability and the proportion of dwarf males. When hermaphrodites appear, all hermaphrodites become protandric simultaneous hermaphrodites. Furthermore, high mortality and poor resource availability favor dwarf males because of their early maturation and weakened sperm competition. In conclusion, we showed that combining sex allocation and life history theories is a useful way to understand various sexual systems in barnacles and perhaps in other organisms as well. (c) 2012 Elsevier Ltd. All rights reserved., Mar. 2013, 320, 1, 9, Scientific journal
  • Not Refereed, NATURWISSENSCHAFTEN, SPRINGER, Postembryonic development of the bone-eating worm Osedax japonicus, Norio Miyamoto; Tomoko Yamamoto; Yoichi Yusa; Yoshihiro Fujiwara, Bone-eating worms of the genus Osedax exclusively inhabit sunken vertebrate bones on the seafloor. The unique lifestyle and morphology of Osedax spp. have received much scientific attention, but the whole process of their development has not been observed. We herein report the postembryonic development and settlement of Osedax japonicus Fujikura et al. (Zool Sci 23:733-740, 2006). Fertilised eggs were spawned into the mucus of a female, and the larvae swam out from the mucus at the trochophore stage. Larvae survived for 10 days under laboratory conditions. The larvae settled on bones, elongated their bodies and crawled around on the bones. Then they secreted mucus to create a tube and the palps started to develop. The palps of O. japonicus arose from the prostomium, whereas the anterior appendages of other siboglinids arose from the peristomium. The recruitment of dwarf males was induced by rearing larvae with adult females. Females started to spawn eggs 6 weeks after settlement., Mar. 2013, 100, 3, 285, 289, Scientific journal
  • Not Refereed, Journal of the Marine Biological Association of the United Kingdom, Effects of photosynthesis on the survival and weight retention of two kleptoplastic sacoglossan opisthobranchs, Shoko Yamamoto; Yayoi M. Hirano; Yoshiaki J. Hirano; Cynthia D. Trowbridge; Ayana Akimoto; Atsushi Sakai; Yoichi Yusa, Many sacoglossan sea slugs utilize chloroplasts ingested from food algae for photosynthesis (functional kleptoplasty), and the extent and duration of kleptoplast retention differs greatly among sacoglossan species. Although most recent studies focus on the genetic, microscopic, or physiological mechanisms responsible for this unique phenomenon, its effects on the life history traits of sacoglossans have not been fully explored. To study the effects of light conditions on survival and weight retention, adult individuals of two sacoglossan species, Elysia trisinuata and Plakobranchus ocellatus (‘black type'), were reared under light conditions (a 14-hour light: 10-hour dark photoperiod with an irradiance level of 28 µmol m−2s−1) or complete darkness for 21 days. There was no significant difference in the survival rate between the light and dark treatments for E. trisinuata, and its wet weight relative to the initial weight was smaller in the light than in the dark. However, both the survival and relative weights were greater in the light than dark for P. ocellatus. Based on the fluorescent yield measurement using pulse-amplitude-modulated fluorometry, the retention duration of functional chloroplasts was longer (> 17 days) for P. ocellatus than E. trisinuata (< 4 days). These results indicate that P. ocellatus benefits from photosynthesis for survival and growth, whereas E. trisinuata does not under starved conditions. This interspecific difference is likely related to the period of functional chloroplast retention. © 2012, Marine Biological Association of the United Kingdom. All rights reserved., 2013, 93, 1, 209, 215, Scientific journal
  • Not Refereed, Cahiers de Biologie Marine, The first finding of the neustonic barnacle Lepas pectinata and nudibranch Fiona pinnata in the deep sea, 遊佐 陽一; Wada, Y; Miura, Y; Fujiwara, Y; Yamamoto, T; Okoshi, K; Yusa, Y, 2013, 49, 295, 297
  • Refereed, INTEGRATIVE AND COMPARATIVE BIOLOGY, OXFORD UNIV PRESS INC, Sexual Systems and Life History of Barnacles: A Theoretical Perspective, Sachi Yamaguchi; Eric L. Charnov; Kota Sawada; Yoichi Yusa, Thoracican barnacles show one of the most diverse sexual systems in animals: hermaphroditism, dioecy (males and females), and androdioecy (males and hermaphrodites). In addition, when present, male barnacles are very small and are called "dwarf males". The diverse sexual systems and male dwarfism in this taxon have attracted both theoretical and empirical biologists. In this article, we review the theoretical studies on barnacles' sexual systems in the context of sex allocation and life history theories. We first introduce the sex allocation models by Charnov, especially in relation to the mating group size, and a new expansion of his models is also proposed. We then explain three studies by Yamaguchi et al., who have studied the interaction between sex allocation and life history in barnacles. These studies consistently showed that limited mating opportunity favors androdioecy and dioecy over hermaphroditism. In addition, other factors, such as rates of survival and availability of food, are also important. We discuss the importance of empirical studies testing these predictions and how empirical studies interact with theoretical constructs., Sep. 2012, 52, 3, 356, 365, Scientific journal
  • Not Refereed, PROTOPLASMA, SPRINGER WIEN, Effects of chloroplast dysfunction on mitochondria: white sectors in variegated leaves have higher mitochondrial DNA levels and lower dark respiration rates than green sectors, Haruka Toshoji; Tomomi Katsumata; Mari Takusagawa; Yoichi Yusa; Atsushi Sakai, Co-ordination between plastids and mitochondria is so essential that there should be extensive inter-organellar crosstalk during development of plant cells. Indeed, chloroplast dysfunction in white leaves of plastid ribosome-deficient mutant barley, albostrians, is reportedly accompanied by increases in the levels of mitochondrial DNA and mitochondrial transcripts, suggesting that (i) developmental/physiological status of plastids (or heterotrophic growth condition of albino leaves) can affect the status of mitochondrial genome, and (ii) the function of the affected mitochondria may also be up-regulated accordingly. However, functional aspects of the mitochondria affected by chloroplast dysfunction have not yet been examined in detail. Here, we examined the effects of chloroplast dysfunction on mitochondrial DNA level and dark respiration rate, by comparing white and green sectors within individual variegated leaves, using 12 ornamental plants as experimental materials. The pattern of leaf variegation differed from species to species, suggesting that different mechanisms were involved in the formation of white sectors in different species. Quantitative hybridization analysis revealed that mitochondrial DNA levels were generally higher in white sectors than in green sectors. In spite of the elevated mitochondrial DNA levels, however, dark respiration rates in white sectors were generally lower than those in green sectors. Several possible mechanisms for elevation of mitochondrial DNA level and suppression of dark respiration rates in white sectors are discussed., Jul. 2012, 249, 3, 805, 817, Scientific journal
  • Not Refereed, BIOLOGICAL INVASIONS, SPRINGER, Predator-driven biotic resistance and propagule pressure regulate the invasive apple snail Pomacea canaliculata in Japan, Yoko Yamanishi; Kazuhiro Yoshida; Noriomi Fujimori; Yoichi Yusa, Species richness in local communities has been considered an important factor determining the success of invasion by exotic species (the biotic resistance hypothesis). However, the detailed mechanisms, especially the role of predator communities, are not well understood. We studied biotic resistance to an invasive freshwater snail, Pomacea canaliculata, at 31 sites in an urban river basin (the Yamatogawa) in western Japan. First, we studied the relationship between the richness of local animal species and the abundance of P. canaliculata, demonstrating a negative relationship, which suggests that the intensity of biotic resistance regulates local snail populations. This pattern was due to the richness of native predator communities rather than that of introduced species or non-predators (mainly competitors of the apple snail). Local snail abundance was also affected by immigration of snails from nearby rice fields (i.e. propagule pressure), where few predators occur. Second, we assessed short-term predation pressure on the snail by means of a tethering experiment. Predation pressure was positively correlated with the number of individual predators and negatively correlated with snail abundance. The introduced crayfish Procambarus clarkii was responsible for the variance in predation pressure. These results indicate that the predator community, composed of both native and introduced species, is responsible for resistance to a novel invader even in a polluted urban river., Jul. 2012, 14, 7, 1343, 1352, Scientific journal
  • Not Refereed, JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY, ELSEVIER SCIENCE BV, Cypris settlement and dwarf male formation in the barnacle Scalpellum scalpellum: A model for an androdioecious reproductive system, U. Spremberg; J. T. Hoeg; L. Buhl-Mortensen; Y. Yusa, Cypris settlement and metamorphosis into dwarf males were studied in the androdioecious barnacle Scalpellum scalpellum using field collected samples from the North Sea, and experiments with laboratory reared larvae, observed with video. In the field sample, dwarf males were always situated on the rim of the mantle aperture and almost invariably confined to two areas (receptacles) located along the scutal plates near their contact to the terga. In the laboratory experiments, cyprids settling on the mantle rim always developed into males. Those settling elsewhere, whether on the external surfaces of the adults, or on their hydroid substratum, always developed into hermaphrodites. The numbers settling as males did not differ significantly from those settling as hermaphrodites, suggesting that genetic sex determination may operate in S. scalpellum. The N. Sea sample comprised 52 adult hermaphrodites. Of these 15(29%) lacked males altogether, while 37(71%) carried males with an average of 4.7 per hermaphrodite. On the hermaphrodite, a thin lamella along the mantle rim protects the settling and metamorphosing male from accidental damage or dislocation by the beating cirri. The cyprid gains additional protection by starting almost immediately after settlement to penetrate into the receptacle tissue. After 12-24 h the developing dwarf male can be almost completely buried. It appears that the cyprid does not use any preformed burrow, but actively descends into the hermaphrodite integument. (C) 2012 Elsevier B.V. All rights reserved., Jul. 2012, 422, 39, 47, Scientific journal
  • Not Refereed, PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, ROYAL SOC, Adaptive evolution of sexual systems in pedunculate barnacles, Yoichi Yusa; Mai Yoshikawa; Jun Kitaura; Masako Kawane; Yuki Ozaki; Shigeyuki Yamato; Jens T. Hoeg, How and why diverse sexual systems evolve are fascinating evolutionary questions, but few empirical studies have dealt with these questions in animals. Pedunculate (gooseneck) barnacles show such diversity, including simultaneous hermaphroditism, coexistence of dwarf males and hermaphrodites (androdioecy), and coexistence of dwarf males and females (dioecy). Here, we report the first phylogenetically controlled test of the hypothesis that the ultimate cause of the diverse sexual systems and presence of dwarf males in this group is limited mating opportunities for non-dwarf individuals, owing to mating in small groups. Within the pedunculate barnacle phylogeny, dwarf males and females have evolved repeatedly. Females are more likely to evolve in androdioecious than hermaphroditic populations, suggesting that evolution of dwarf males has preceded that of females in pedunculates. Both dwarf males and females are associated with a higher proportion of solitary individuals in the population, corroborating the hypothesis that limited mating opportunities have favoured evolution of these diverse sexual systems, which have puzzled biologists since Darwin., Mar. 2012, 279, 1730, 959, 966, Scientific journal
  • Not Refereed, JOURNAL OF ETHOLOGY, SPRINGER TOKYO, Courtship tactics by male Ilyoplax pusilla (Brachyura, Dotillidae), Asami Kasatani; Keiji Wada; Yoichi Yusa; John H. Christy, Mating in the dotillid crab Ilyoplax pusilla occurs after the female enters the male's burrow in the tidal flat. Males use two tactics to cause females to enter their burrows for mating: the male either directs claw waving to the female (courting-wave display), to which the females responds by following the male to his burrow, or the male runs rapidly away from, then back toward, his burrow (dash-out-back display), which startles the female into his burrow. Males more often used the courting-wave than the dash-out-back display, but mating success did not differ between the two tactics. Male use of either tactic was influenced by date, female density and male size; the courting-wave display was used by larger males, later in the breeding period, and under higher female density., Jan. 2012, 30, 1, 69, 74, Scientific journal
  • Not Refereed, FRESHWATER BIOLOGY, WILEY, Indirect interactions in a rice ecosystem: density dependence and the interplay between consumptive and non-consumptive effects of predators, Haruko Yoshie; Yoichi Yusa, P>1. Density- and trait-mediated indirect interactions (DMIIs and TMIIs, respectively) in food chains play crucial roles in community structure and processes. However, factors affecting the relative strength of these interactions are poorly understood, including in widespread and important freshwater rice ecosystems.2. We studied the strength of DMIIs and TMIIs in a food chain involving a predator (the Reeve's turtle Chinemys reevesii), its herbivorous prey (the apple snail Pomacea canaliculata) and a plant (rice Oryza sativa) in outdoor containers simulating rice fields. We also evaluated consumptive and non-consumptive effects of the predator on the snail. We removed a fixed proportion of snails every 2 days to simulate prey consumption and introduced a caged turtle that was fed daily with snails to simulate non-consumptive effects.3. Direct consumptive effects increased growth of the remaining snails and their per capita feeding rate. Moreover, consumptive and non-consumptive effects, and their interaction, affected the proportion of snails buried in the soil. This interaction was presumably because increasing food availability per snail induced their self-burying behaviour.4. Both DMIIs and TMIIs affected the number of rice plants remaining, whereas their interaction term was not significant.5. In summary, density dependence and interactions between consumptive and non-consumptive effects influenced snail growth and behaviour, respectively. However, no cascading effects of these complicated interactions on rice plants were detected., Feb. 2011, 56, 2, 302, 310, Scientific journal
  • Not Refereed, BIOLOGICAL BULLETIN, MARINE BIOLOGICAL LABORATORY, Dwarf Males of Octolasmis warwickii (Cirripedia: Thoracica): The First Example of Coexistence of Males and Hermaphrodites in the Suborder Lepadomorpha, Yoichi Yusa; Mayuko Takemura; Katsumi Miyazaki; Tetsuya Watanabe; Shigeyuki Yamato, In the lepadomorph barnacle Octolasmis warwickii, individuals are often found attached to the scutum of conspecifics living externally on the crab hosts. To test whether these conspecific-attached individuals are dwarf males, as are known to occur in other suborders of barnacles, we compared the pattern of attachment, size-frequency distribution, and reproductive status of the conspecific-attached (Con-A) and crab-attached (Crab-A) individuals. Con-As were smaller than Crab-As. There was a positive relationship between the body size of Crab-As and the number of individuals on them. Con-As had longer penises than Crab-As of the same body size, and their testes were better developed. The four largest Con-As examined were brooding eggs. These results indicate that Con-As of O. warwickii are dwarf males, with a potential to become hermaphroditic. This represents the first known example of coexistence of males and hermaphrodites in the suborder Lepadomorpha. The mating group size of O. warwickii was smaller than in its hermaphroditic congeners but larger than in barnacles with dwarf males and females, which supports the current theories that group size is important for the evolution of sexuality patterns in barnacles., Jun. 2010, 218, 3, 259, 265, Scientific journal
  • Not Refereed, MARINE BIOLOGY, SPRINGER, Effects of temperature and food availability on growth and reproduction in the neustonic pedunculate barnacle Lepas anserifera, Ayano Inatsuchi; Shigeyuki Yamato; Yoichi Yusa, To elucidate the life history of neustonic animals, growth and reproductive patterns were investigated in the hermaphroditic pedunculate barnacle Lepas anserifera in field and laboratory experiments in Wakayama, western Japan from 2006 to 2008. The effects of temperature (19, 24 or 29A degrees C) and food availability (once or twice a week) on growth and reproduction were also studied in the laboratory. The barnacles grew and matured rapidly, especially in the field: individuals on the average grew from 3 mm to more than 12 mm in capitulum length within 15 days and some were brooding. High temperature and high food availability resulted in greater growth. High temperature also resulted in earlier maturation of both testes and ovaries, whereas the effect of food availability was less clear. The rapid growth and maturation, together with earlier maturation at higher temperatures, may be an adaptation to ephemeral floating objects to which they attach., Apr. 2010, 157, 4, 899, 905, Scientific journal
  • Not Refereed, MALACOLOGIA, INST MALACOL, LEARNED PREDATOR RECOGNITION IN A FRESHWATER SNAIL, POMACEA CANALICULATA, Kahori Aizaki; Yoichi Yusa, The involvement of associative learning in predator recognition has not been clear in aquatic invertebrates, including molluscs, due to confounding effects of sensitization. The freshwater apple snail, Pomacea canaliculata, displays an alarm response (crawling above the waterline) when exposed to crushed conspecifics or some predators. We conducted two series of experiments to investigate whether the apple snail learns to avoid predators. In the first experiment, hatchlings were conditioned simultaneously to crushed conspecifics and either a live carp, Cyprinus carpio, or a turtle, Chinemys reevesii, and subsequently exposed to the same predator without crushed conspecifics. Irrespective of the predator species used, the alarm response was significantly higher in conditioned snails than in unconditioned snails. Thus, the snail is able to avoid predators by learning, in a broad sense. In the second experiment, designed to distinguish associative learning from sensitization, we conditioned hatchlings to crushed conspecifics and either a carp or a turtle. The hatchlings were subsequently exposed to one or other of the predators. Hatchlings that were conditioned to a predator displayed significantly higher alarm response when later exposed to the same predator than another predator, suggesting that the snail can recognize predators by associative learning., 2010, 52, 1, 21, 29, Scientific journal
  • Not Refereed, APPLIED ENTOMOLOGY AND ZOOLOGY, JAPAN SOC APPL ENTOMOL ZOOL, Life cycle of the apple snail Pomacea canaliculata (Caenogastropoda: Ampullariidae) inhabiting Japanese paddy fields, Kazuhiro Yoshida; Kazuo Hoshikawa; Takashi Wada; Yoichi Yusa, The life cycle of the apple snail Pomacea canaliculata was monitored over 2- and 1-year periods in Nara (cold district) and Kumamoto (warm district), respectively. The life cycles were similar in both districts: most hatchlings appeared after August, and although some had grown to >= 20 mm by autumn, the majority of juveniles remained <20 mm. The survival rate over winter was very low (<1%) in Nara, and moderately low (9%) in Kumamoto. After winter, survivors grew rapidly with low mortality, reproduced actively in summer, and most died during the following winter. The survival rate during mid-term drying (drying of fields for about 2 weeks in summer) in Nara was high (ca. 90%) in both years. In Nara, snail density after winter decreased to 1/43 of that in Kumamoto, but survivors in Nara grew larger and laid more eggs. Due to these effects,. egg density in July, and also snail density in September, in Nara recovered to ca. 1/3 of that in Kumamoto., Aug. 2009, 44, 3, 465, 474, Scientific journal
  • Not Refereed, EVOLUTIONARY ECOLOGY RESEARCH, EVOLUTIONARY ECOLOGY LTD, Evolution of dwarf males and a variety of sexual modes in barnacles: an ESS approach, Satoru Urano; Sachi Yamaguchi; Shigeyuki Yamato; Satoshi Takahashi; Yoichi Yusa, Questions: Why do barnacles have many modes of sexuality, including hermaphroditism, androdioecy (large hermaphrodites with dwarf males), and dioecy (large females with dwarf males)? Can mating group size, relative body size, competitive advantage or survival rate of dwarf male individuals explain which type of sexuality is favoured by natural selection? Mathematical methods: We developed an ESS model to investigate factors affecting the optimal proportion of larvae that become dwarf males (q*). Allocation to male function of large hermaphrodites is calculated according to Charnov's sex allocation theory, although sperm competition with dwarf males is taken into account. Our model is based on a life history of androdioecious barnacles, which includes hermaphroditism (q* = 0) and dioecy (q* > 0 and the male allocation of large hermaphrodites = 0) as special cases. We incorporate average mating group size (m) into the model, together with body size, competitive advantage, and survival rate of dwarf males relative to large hermaphrodites. Results: The proportion of dwarf males, q*, increases from 0 (hermaphroditism) as mating group size decreases, and approaches 0.5 when group size, m, nears 0. At the latter extreme, large individuals should become females instead of hermaphrodites. Thus mating group size can explain the major trend of sexuality in barnacles: hermaphroditism in relatively large mating groups, androdioecy in smaller groups, and dioecy in even smaller groups. Relative body size, competitive advantage, and survival rate of dwarf males all have positive effects on the evolutionarily stable proportion of males. If there is a simple trade-off between body size and survival rate, survival rate will have the greater influence on sexuality., Jul. 2009, 11, 5, 713, 729, Scientific journal
  • Not Refereed, JOURNAL OF ETHOLOGY, SPRINGER TOKYO, Field observations of the alarm response to crushed conspecifics in the freshwater snail Pomacea canaliculata: effects of habitat, vegetation, and body size, Kahori Aizaki; Yoichi Yusa, The freshwater snail Pomacea canaliculata shows alarm responses to chemical cues released from injured conspecifics, but its behavioural responses in the field are unknown. We investigated effects of habitat (canals or paddy fields), vegetation, and body size on alarm responses in the field. Snails responded to crushed conspecifics within 4 min by burying themselves, but the proportions of self-buried snails were generally lower (0-28% depending on experiments) than those reported in the laboratory. Snails not only showed the alarm response, but also frequently fed on crushed conspecifics. There were no influences of habitat or body size on the proportions of individuals showing the alarm response. Nevertheless, in paddy fields with high-density vegetation a higher proportion of snails showed the alarm response than in paddy fields with low-density vegetation., Jan. 2009, 27, 1, 175, 180, Scientific journal
  • Not Refereed, 九州病害虫研究会報, 西南日本において水田から用水路に流出するスクミリンゴガイの個体数, 遊佐 陽一; 和田節; 松倉啓一郎; 吉田和弘; 山西陽子; 遊佐陽一, 2009, 55, 93, 98
  • Not Refereed, Endocytobiosis Cell Research, Identification of photosynthetic sacoglossans from Japan, Yamamoto, Y. Y; Yusa, Y; thers, 2009, 19, 112, 119
  • Not Refereed, APPLIED ENTOMOLOGY AND ZOOLOGY, SPRINGER JAPAN KK, Effects of predation on the exotic freshwater snail Pomacea canaliculata (Caenogastropoda: Ampullariidae) by the indigenous turtle Chinemys reevesii (Testudines: Geoemydidae), Haruko Yoshie; Yoichi Yusa, We studied the predatory potential of the turtle Chinemys reevesii on the apple snail Pomacea canaliculata using two series of experiments. First, we investigated the relationship between turtle body size and the maximum size of snails consumed over a period of 3 days within 0.37 m(2) containers. The maximum snail size consumed was positively related with turtle size. Secondly, we investigated the predation of snails by turtles over a period of 8 weeks. We released 200 snails (10-30 mm shell height) and an adult turtle (155-183 mm carapace length) into each of two 2.08 m(2) plots with soil and rice plants. Subsequently, snail density was monitored every week and 200 snails were added to low density plots up to twice a week. Two control plots with the same initial density of snails but without turtles were also monitored. The density and survival rate of snails were lower in plots with a turtle than in control plots. We estimated that a single turtle consumed >2,000 snails in 8 weeks. In addition, the biomass of duckweed (given as food for snails) was greater in turtle plots than in control plots, suggesting that the presence of turtles had an indirect effect on weed., Nov. 2008, 43, 4, 475, 482, Scientific journal
  • Not Refereed, JOURNAL OF THEORETICAL BIOLOGY, ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, Mating group size and evolutionarily stable pattern of sexuality in barnacles, Sachi Yamaguchi; Yoichi Yusa; Shigeyuki Yamato; Satoru Urano; Satoshi Takahashi, Barnacles, marine crustaceans, have various patterns of sexuality depending on species including simultaneous hermaphroditism, androdioecy (hermaphrodites and dwarf males), and dioecy (females and dwarf males). We develop a model that predicts the pattern of sexuality in barnacles by two key environmental factors: (i) food availability and (ii) the fraction of larvae that settle on the sea floor. Populations in the model consist of small individuals and large ones. We calculate the optimal resource allocation toward male function, female function and growth for small and large barnacles that maximizes each barnacle's lifetime reproductive success using dynamic programming. The pattern of sexuality is defined by the combination of the optimal resource allocations. In our model, the mating group size is a dependent variable and we found that sexuality pattern changes with the food availability through the mating group size: simultaneous hermaphroditism appears in food-rich environments, where the mating group size is large, protandric simultaneous hermaphroditism appears in intermediate food environments, where the mating group size also takes intermediate value, the other sexuality patterns, androdioecy, dioecy, and sex change are observed in food-poor environments, where the mating group size is small. Our model is the first one where small males can control their growth to large individuals, and hence has ability to explain a rich spectrum of sexual patterns found in barnacles. (c) 2008 Elsevier Ltd. All rights reserved., Jul. 2008, 253, 1, 61, 73, Scientific journal
  • Not Refereed, Invertebrate Biology, Size-dependent sex allocation and sexual selection in Aplysia kurodai, a hermaphrodite with nonreciprocal mating, Yoichi Yusa, For simultaneous hermaphrodites, a male-to-female shift in sex allocation with growth, and weak sexual selection on the male function, is predicted by many theories, although empirical data for both predictions are insufficient for internally fertilizing hermaphrodites with nonreciprocal mating. To address these issues, I studied mating and egg-laying behavior of the sea hare, Aplysia kurodai (Gastropoda: Opisthobranchia) in the laboratory. Both frequency and duration of egg laying increased with body weight, indicating that fecundity increased with weight. On the other hand, frequency and duration of mating as males did not increase with body weight, suggesting that sperm usage was independent of weight. Therefore, sex allocation shifted from male to female functions with growth. The lack of a relationship between body weight and mating activities as males also suggests that there was no "female" choice for large partners. However, the frequency of mating as females increased with body weight, suggesting "male" choice for large partners. This "male" choice is further supported by the presence of size-assortative mating and a longer duration of mating when the female partner was large. In addition, the variance in mating frequency as females was larger than that as males. As a whole, the mating behavior in A. kurodai can be summarized as choosy as males and unchoosy as females, the opposite of the patterns known in most gonochoric and hermaphroditic animals. © 2008, The Authors. Journal compilation © 2008, The American Microscopical Society, Inc., Jun. 2008, 127, 3, 291, 298, Scientific journal
  • Not Refereed, JOURNAL OF THE MARINE BIOLOGICAL ASSOCIATION OF THE UNITED KINGDOM, CAMBRIDGE UNIV PRESS, Reproductive ecology of the pedunculate barnacle Scalpellum stearnsii (Cirripedia : Lepadomorpha : Scalpellidae), Yuki Ozaki; Yoichi Yusa; Shigeyuki Yamato; Tohru Imaoka, The sexuality of large (non-dwarf) individuals and the characteristics of eggs, larvae and dwarf males were investigated in the pedunculate barnacle Scalpellum stearnsii. All 103 large individuals collected in this study were not hermaphrodites but females. The major length axis of the egg was on average 0.50 mm, which was larger than that in most thoracican barnacles with planktotrophic larvae. The larvae hatched as nauplii and metamorphosed into cyprids without feeding (i.e. lecithotrophic development). There was a positive relationship between body weight and egg mass weight in ovigerous females. The number of males attached per female ranged from 0 to 35 (average: 5.9) and there was a positive relationship between the number of males and female body weight. The distribution of dwarf males was skewed significantly towards the lower part of the occludent margin, which is near the fertilization site., Feb. 2008, 88, 1, 77, 83, Scientific journal
  • Not Refereed, Venus, スクミリンゴガイの殻厚に影響する要因, 遊佐 陽一; 吉田和弘; 遊佐陽一; 和田節; 星川和夫, 2008, 66, 217, 225
  • Not Refereed, AMERICAN MALACOLOGICAL BULLETIN, AMER MALACOLOGICAL SOC, INC, Causes of variation in sex ratio and modes of sex determination in the Mollusca - an overview, Yoichi Yusa, The mechanisms for variation in the primary and apparent sex ratios, from both theoretical and empirical perspectives, are reviewed. A series of experiments on the sex ratios and mode of sex determination in the apple snail Pomacea canaliculata (Lamarck, 1822) show that broods have highly variable sex ratios even though the sex ratios of populations are 1:1. I suggest that the mechanism responsible for this pattern is oligogenic sex determination, i.e., sex determination by a small number of genes. Two other molluscan groups, the protandric oysters of the genus Crassostrea Sacco, 1897, and mussels of the genus Mytilus Linnaeus, 1758 also show variable sex ratios. In both cases, the number of genes responsible for the variation appears to be small., Dec. 2007, 23, 1-2, 89, 98, Scientific journal
  • Not Refereed, JOURNAL OF MOLLUSCAN STUDIES, OXFORD UNIV PRESS, A water-borne sex pheromone and trail following in the apple snail, Pomacea canaliculata, Mari Takeichi; Yoshio Hirai; Yoichi Yusa, We investigated whether individuals of the apple snail Pomacea canaliculata were attracted by conspecifics or follow mucus trails of other individuals. The snails' behaviour was studied by a series of choice experiments in a T-maze and in Petri dishes. Both males and females chose the side with a snail of the opposite sex significantly more frequently than the control side without a snail. Males were attracted by water conditioned with females more frequently than unconditioned water, whereas females did not show a preference for male-conditioned water. Moreover, juveniles were not attracted by water conditioned with a male, a female and a juvenile. These data indicate that males were attracted by female odour, which contains one or more water-borne sex pheromones. In addition, both males and females follow mucus trails of snails of the opposite sex. Since females also followed trails of females, the function of trail following is not necessarily related to reproduction. In these experiments P. canaliculata did not distinguish the direction of the trail., Aug. 2007, 73, 275, 278, Scientific journal
  • Not Refereed, JOURNAL OF THEORETICAL BIOLOGY, ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, Do tiny males grow up? Sperm competition and optimal resource allocation schedule of dwarf males of barnacles, Sachi Yamaguchi; Yuki Ozaki; Yoichi Yusa; Satoshi Takahashi, Barnacles, marine crustaceans, have three sexual patterns: simultaneous hermaphroditism, dioecy and androdioecy. In dioecy and androdioecy, large individuals (females and hermaphrodites, respectively) are attached by dwarf males. Depending on species, some dwarf males grow up, others do not in their life time. To investigate which environmental conditions affect growth patterns of dwarf males of barnacles, we investigate the evolutionarily stable life history strategy of dwarf males using Pontryagin's maximum principle. Sperm competition among dwarf males and that among dwarf males and large hermaphrodites is taken into account. Dwarf males grow up in food-rich environments, while they do not grow at all in food-poor environments. ESS of the resource allocation schedule between reproduction and growth follows an "intermediate growth strategy" (simultaneous growth and reproduction) for dioecious species, in which sperm competition is not severe. On the other hand, it approaches "bang-bang control" (switching from allocating all resources toward growth then to reproduction), as sperm competition against surrounding large hermaphrodites becomes severe in androdioccious species. (c) 2006 Elsevier Ltd. All rights reserved., Mar. 2007, 245, 2, 319, 328, Scientific journal
  • Not Refereed, Genetics, Nuclear sex-determining genes cause large sex-ratio variation in the apple snail Pomacea canaliculata, Yoichi Yusa, Evolutionary maintenance of genetic sex-ratio variation is enigmatic since genes for biased sex ratios are disadvantageous in finite populations (the "Verner effect"). However, such variation could be maintained if a small number of nuclear sex-determining genes were responsible, although this has not been fully demonstrated experimentally. Brood sex ratios of the freshwater snail Pomacea canaliculata are highly variable among parents, but population sex ratios are near unity. In this study, the effect of each parent on the brood sex ratio was investigated by exchanging partners among mating pairs. There were positive correlations between sex ratios of half-sib broods of the common mother (r = 0.42) or of the common father (r = 0.47). Moreover, the correlation between full-sib broods was very high (r = 0.92). Thus, both parents contributed equally to the sex-ratio variation, which indicates that nuclear genes are involved and their effects are additive. Since the half-sib correlations were much stronger than the parent-offspring regressions previously obtained, the variation was caused by zygotic sex-determining genes rather than by parental sex-ratio genes. The number of relevant genes appears to be small. Copyright © 2007 by the Genetics Society of America., Jan. 2007, 175, 1, 179, 184, Scientific journal
  • Not Refereed, APPLIED ENTOMOLOGY AND ZOOLOGY, SPRINGER JAPAN KK, Effects of dormant duration, body size, self-burial and water condition on the long-term survival of the apple snail, Pomacea canaliculata (Gastropoda : Ampullariidae), Yoichi Yusa; Takashi Wada; Satoshi Takahashi, We investigated factors influencing the survival of the apple snail, Poinacea canalicidata during dormancy in the laboratory at 20-26 degrees C. We placed snails of three size classes in small pots with soil and water, drained the water to induce self-burial, and subsequently checked the snails' survival at intervals. The duration of the dormant period, body size and the success of self-burial all affected the survival of the snails. The effects of water conditions (dry or moist) affected the survival of the snails through interactions with body size and duration. The longest duration of survival under dry conditions was 11 months, and a small proportion of medium-sized and large snails survived the entire experimental period of 29 months under moist conditions., Nov. 2006, 41, 4, 627, 632, Scientific journal
  • Not Refereed, BIOLOGICAL INVASIONS, SPRINGER, Predatory potential of freshwater animals on an invasive agricultural pest, the apple snail Pomacea canaliculata (Gastropoda : Ampullariidae), in southern Japan, Y Yusa; N Sugiura; T Wada, The apple snail Pomacea canaliculata is an invasive species and a serious pest of rice in many Asian countries. We studied predatory activities of various animals living in Japanese freshwater habitats, by keeping each individual of a potential predator species with 36 snails of various sizes for three days in the aquarium. Forty-six species were tested, and 26 in eight classes fed on small snails. A species of leech, crabs, the common carp, turtles, the mallard duck and the Norway rat attacked even adult snails of 20-30 mm in shell height. These findings will be helpful in identifying effective predators for biological control of the pest snail. In addition, most of the animals attacking snails are reported to be common in rivers or ponds, but few live in modernized paddy fields having little connections with natural water systems. This may be a reason why this snail maintains large populations in paddy fields but not in other freshwater habitats., Mar. 2006, 8, 2, 137, 147, Scientific journal
  • Not Refereed, Heredity, Genetics of sex-ratio variation inferred from parent-offspring regressions and sib correlations in the apple snail Pomacea canaliculata, Y. Yusa, The brood sex ratio in the apple snail Pomacea canaliculata varies almost continuously from all male to all female, but the population sex ratio is nearly 1:1. In this study, regressions of the offspring sex ratio on the sex ratios of the parents' siblings as well as correlations in the brood sex ratios between sisters or brothers were investigated, in order to infer the genetic system that produces the sex-ratio pattern. There were significant positive relationships between the offspring sex ratio and the sex ratio of the mother's siblings (slope = 0.28), and between the offspring sex ratios of two sisters (r = 0.41). On the other hand, the father-offspring regression (slope = 0.10), and the correlations between two brothers (r = -0.13) or between the brother and the sister (r = 0.17) were not significant. These patterns differed from predictions using typical cytoplasmic sex factors, sex-ratio genes or sex-determining polygenes. Thus, the results suggest the involvement of either a small number of sex-determining genes or a more complicated system such as sex-ratio or sex-determining polygenes that act non-additively. © 2006 Nature Publishing Group All rights reserved., Jan. 2006, 96, 1, 100, 105, Scientific journal
  • Not Refereed, APPLIED ENTOMOLOGY AND ZOOLOGY, JAPAN SOC APPL ENTOMOL ZOOL, Decrease in density of the apple snail Pomacea canaliculata (Lamarck) (Gastropoda : Ampullariidae) in paddy fields after crop rotation with soybean, and its population growth during the crop season, T Wada; K Ichinose; Y Yusa; N Sugiura, We compared the densities of the apple snail, Pomacea canaliculata, between fields that had been planted with soybean or rice in the previous summer. The densities of overwintered snails soon after irrigation at the beginning of rice planting were all very low in the fields after soybean. These values were much lower than the control threshold for the apple snail in direct seeding. Therefore, crop rotation with soybean seems to be a good economic measure to control the apple snail in direct seeding. The snail populations increased very rapidly in both types of fields, in particular, after soybean. Within two and a half summer months, the snail densities in the fields after soybean reached almost the same level as those in the fields after rice. This rapid population recovery in fields after soybean seems to be caused by density-dependent growth and reproduction in this species., Aug. 2004, 39, 3, 367, 372, Scientific journal
  • Not Refereed, Kyushu Pl. Prot Res., The Association for Plant Protection of Kyushu, Decrease in density of the apple snail, Pomacea canaliculata (Lamarck) (Gastropoda: Ampullariidae) by tillage and soil puddling., Wada Takashi; Yusa Yoichi; Ichinose Katsuya; Kanno Hiroo; Matsumura Masaya; Arimura Kazuhiro; Urano Satoru; Takahashi Kimiyasu, Mortality of the apple snail, Pomacea canaliculata, caused by tillage or soil puddling was examined in rice fields. Tillage greatly decreased the snail density with ca. 75% mortality when the mean shell height of snails was 20.3 mm (±4.3;S.D.). However, "intensive tillage" using a special rotary cultivator with a smaller rotary pitch, and taking more time than ordinary tillage. had no additional effect on snail mortality. Soil puddling also attained a 67% mortality rate for snails with a mean shell height of 20.4 mm (±5.3:S.D.). When smaller snails (mean shell height: 11.8±5.4 mm) occurred in a field, 68% mortality was attained by tillage plus soil puddling. One of the examples revealed that a density of 4.5 overwintering snails per m2 in a field was finally reduced to 0.3 snails per m2 by tillage plus two occasions of soil puddling. Thus, tillage and soil puddling are good methods for decreasing snail density before rice planting., 2004, 50, 23, 28
  • Not Refereed, Journal of Molluscan Studies, Brood sex ratio in the apple snail Pomacea canaliculata (Gastropoda: Ampullariidae) is determined genetically and not by environmental factors, YUSA Yoichi; Y. Yusa, 2004, 70, 269, 275
  • Not Refereed, Journal of Molluscan Studies, Inheritance of colour polymorphism and the pattern of sperm competition in the apple snail Pomacea canaliculata (Gastropoda: Ampullariidae), YUSA Yoichi; Y. Yusa, 2004, 70, 43, 48
  • Not Refereed, ECOLOGICAL RESEARCH, BLACKWELL PUBLISHING ASIA, Alarm response of hatchlings of the apple snail, Pomacea canaliculata (Gastropoda : Ampullariidae), to aqueous extracts of other individuals, K Ichinose; Y Yusa; K Yoshida, We examined how hatchlings of the freshwater snail, Pomacea, canaliculata, responded to aqueous extracts of conspecific hatchlings. Three, 3-day-old hatchlings were macerated in delonized water (1 mg hatchling per 1 ml water). When 0.5 ml of the aqueous extract was added to a test tube containing 10 hatchlings of the same age and 5 0 ml of water, the hatchlings in the water began to crawl out of the water within 5 min. The proportion of hatchlings that crawled out of the water approached 0.6-0.9 after I h, but gradually decreased to 0.4 after 24 h. The relatedness between the live and the macerated hatchlings had no significant influence on the response. Hatchlings of egg masses obtained either in the laboratory or in the wild responded similarly to aqueous extracts of hatchlings from either egg mass. This suggests that the conditions under which the egg masses were incubated or the conditions that their parents had experienced had no effect on the hatchlings' response. When compared with experiments reported on other aquatic animals, we consider the behavior of the hatchlings to be an alarm response of escaping from predators., Mar. 2003, 18, 2, 213, 219, Scientific journal
  • Not Refereed, PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, ROYAL SOC, A snail with unbiased population sex ratios but highly biased brood sex ratios, Y Yusa; Y Suzuki, Extraordinary sex ratio patterns and the underlying sex-determining mechanisms in various organisms are worth investigating, particularly because they shed light on adaptive sex-ratio adjustment. Here, we report an extremely large variation in the brood sex ratio in the freshwater snail, Pomacea canaliculata. In eight rearing series originating from three wild populations, sex ratios were highly variable among broods, ranging continuously from almost exclusively males to almost exclusively females. However, sex ratios were similar between broods from the same mating pair, indicating that sex ratio is a family trait. Irrespective of the large variations, the average sex ratios in all rearing series were not significantly different from 0.5. We argue that Fisher's adaptive sex-ratio theory can explain the equal average sex ratios, and the results, in turn, directly support Fisher's theory. Polyfactorial sex determination (in which sex is determined by three or more genetic factors) is suggested as the most likely mechanism producing the variable brood sex ratio., Feb. 2003, 270, 1512, 283, 288, Scientific journal
  • Not Refereed, APPLIED ENTOMOLOGY AND ZOOLOGY, SPRINGER JAPAN KK, Effects of food availability and age on the reproductive effort of the apple snail, Pomacea canaliculata (Lamarck) (Gastropoda : Ampullariidae), GF Estoy; Y Yusa; T Wada; H Sakurai; K Tsuchida, The effects of food availability and age on the reproductive traits of Pomacea canaliculata were determined in snails fed at three food levels under laboratory conditions (14L:10D; 25degreesC). In males, copulation frequency tended to increase with age, while food availability did not affect copulation frequency. In females, spawn production was lower in food-limited conditions, but current or weight-specific reproductive effort (RE) did not differ among food levels. The weight-specific RE and spawn frequency of the well-fed females decreased with age, but their current RE increased with age., Nov. 2002, 37, 4, 543, 550, Scientific journal
  • Not Refereed, INTERNATIONAL JOURNAL OF PEST MANAGEMENT, TAYLOR & FRANCIS LTD, Influence of common carp on apple snail in a rice field evaluated by a predator-prey logistic model, K Ichinose; M Tochihara; T Wada; N Suguiura; Y Yusa, The hypothesis that common carp can be used for the control of apple snails in rice fields was tested experimentally. In a rice field, 12 plots of 465 m were set and enclosed by plastic walls to prevent snail emigration and immigration. The experiment continued from June to September. Three replicated treatments were used for the plots: zero, four and 12 carp were released, giving carp densities of 0.0, 0.2 and 0.6 m(-2), respectively. Snail densities were estimated by the Jolly - Seber mark - recapture method. Newly laid egg masses were counted and measured for size, and hatching was monitored. The numbers of eggs per egg mass (y) were estimated using a regression equation obtained from the product of the maximum length and width of the egg mass (x): y= 0.10x(1.24). Using these measures and the monthly mean hatching rate obtained from eggs laid in two outdoor aquaria from April to September, the number of hatched eggs was used to estimate the birth rate over a given time. A logistic model incorporating these estimates revealed that the snail population proliferated only in the zero-carp plot throughout the experiment. The study, together with other reports on snail longevity, predicts that a snail population would be eliminated in 2 years at a stocking density of 2000 carp hectare(-1), if no immigration of the snail occurred., Apr. 2002, 48, 2, 133, 138, Scientific journal
  • Not Refereed, APPLIED ENTOMOLOGY AND ZOOLOGY, SPRINGER JAPAN KK, Size and age at first copulation and spawning of the apple snail, Pomacea canaliculata (Gastropoda : Ampullariidae), GF Estoy; Y Yusa; T Wada; H Sakurai; K Tsuchida, The size and age at first copulation and spawning of the apple snail, Pomacea canaliculata, were determined at three food levels under laboratory conditions (14L:10D; 25degreesC). Males fed at a low food level started copulation at smaller sizes than males at higher food levels. However, age at first copulation was similar among snails at all food levels. The food level appeared to affect the penis sheath length at maturity, although the difference did not reach a statistically significant level. Females fed at the low food level delayed both first copulation and spawning longer than those at higher food levels. Consequently, their sizes at first copulation and spawning were smaller. The albumen gland of poorly fed snails was smaller at first copulation but comparable at maturity, The adaptive significance of these patterns in sexual maturity and their possible implications for the integrated management of this snail are discussed,, Feb. 2002, 37, 1, 199, 205, Scientific journal
  • Not Refereed, JOURNAL OF THE MARINE BIOLOGICAL ASSOCIATION OF THE UNITED KINGDOM, CAMBRIDGE UNIV PRESS, Ecology of a parasitic barnacle, Koleolepas avis: relationship to the hosts, distribution, left-right asymmetry and reproduction, Y Yusa; S Yamato; M Marumura, The pedunculate barnacle Koleolepas avis is a symbiont of the sca anemone Calliactis japonica, which lives on gastropod shells carried by large hermit crabs, usually Dardanus arrosor. Relationships with the host sea anemone, distribution on the gastropod shell, left-right asymmetry and reproduction of the barnacle were investigated. A larger number of barnacles occurred on shells with greater 'cylindroid dimensions' of sea anemones. Distribution of barnacles on shells was not random: assuming the in situ position of the shell carried by the hermit crab (similar to 45 degrees inclination), there were more barnacles along the lower part of the anemone disk than the upper part. Large barnacles lie on either the left or right sides of their capitula, and those lying on the left side (Type L individuals) tended to occur along the left side of the host, and those on the right side (Type R) along the right side. Barnacles greater than or equal to 0.016 g in wet weight had egg masses, and there was a positive relationship between body weight and number of eggs. Koleolepas avis has both hermaphrodites and dwarf (complementary) males attached to them. Large hermaphrodites tended to have larger dwarf males than smaller hermaphrodites., Oct. 2001, 81, 5, 781, 788, Scientific journal
  • Not Refereed, JOURNAL OF MOLLUSCAN STUDIES, OXFORD UNIV PRESS, Predation on eggs of the apple snail Pomacea canaliculata (Gastropoda : Ampullariidae) by the fire ant Solenopsis geminata, Y Yusa, A field survey and two experimental manipulations were made to investigate the extent of predation on eggs of the apple snail Pomacea canaliculata (Lamarck) by the fire ant Solenopsis geminata (Fabricius) in the Philippines. First, when Pomacea egg masses found along levees of paddy fields were observed, more than half of them had some damage. More fire ants were observed near egg masses with higher degrees of damage. Secondly, when egg masses were experimentally placed on levees, on average 50% of the eggs were lost (removed or damaged) within two days in March and 38% were lost within three days in August. Thirdly, egg masses were placed in cups with or without water on levees; no eggs were lost when ants were successfully excluded by water. The proportion of lost eggs was highly variable among egg masses, but there was no difference between day and night. Possible use of this ant as a biocontrol agent for the apple snail is considered., Aug. 2001, 67, 275, 279, Scientific journal
  • Not Refereed, 九州病害虫研究会報, 九州病害虫研究会, 殺貝剤施用と落水管理を組み合わせた湛水直播水稲におけるスクミリンゴガイの食害防止, 遊佐 陽一; 和田 節他, 2001, 47, 58, 64
  • Not Refereed, Kyushu Pl. Prot Res., The Association for Plant Protection of Kyushu, Predatory potential of the common carp, Cyprinus carpio L., on the apple snail, Pomacea canaliculata (Lamarck), in the field., Yusa Yoichi; Kai Shinichiro; Ando Shunji; Shiozaki Naomi; Wada Takashi, We assessed the predatory potential of the common carp on the apple snail at a low density of carp. We released 1 carp (average body length : 16cm) and 1, 400 snails (average weight 0.12g) in each of 23 m2 plots set in a paddy field without rice in August 2000. Seven days after release, snail density was significantly lower in carp-occupied plots than in carp-free ones. However, in a 1 x 1 m cage set in each plot, which excluded carp, neither density of surface snails nor survival rate was different between carp-occupied and carp-free plots. This indicates that predation by carp was responsible for the reduction of the density of surface snails in carp-occupied plots, rather than the increase in the proportion of snails buried or natural snail mortality in the presence of carp. The average predation rate of a carp was estimated to be 54 snails/day. which was about one-fourth of the rate observed in the laboratory. However, the predation rate in the field was high enough to regard carp as biocontrol agents for the snail, not only in rice fields but also in other freshwater systems., 2001, 47, 69, 72
  • Refereed, Kyushu Pl. Prot Res., The Association for Plant Protection of Kyushu, Influence of habitat differences brought about by envvironmental changes on the densities of adults and eggs of Pomacea canaliculata., Ichinose Katsuya; Wada Takashi; Yusa Yoichi; Kubota Tomijiro, The density of Pomacea canaliculata (Lamarck) with shell lengths > 25 mm and of its egg masses were estimated in three habitats: rice field, canal and river. The mean densities were 3.72 ± 1.31, 2.12 ± 0.90 and 3.20 ± 1.85 snails/m2, respectively: no significant difference was detected by ANOVA. In contrast, the mean densities of egg masses, 1.84 ± 0.40, 0.72 ± 0.24 and 0.39 ± 0.19 eggs/m2, differed significantly between rice field and canal and between rice field and river, though not between canal and river. Correlation of these densities with water depth, current velocity, chemical oxygen demand (COD), and predator fauna (Carassius spp., Zacco temmincki, Procambarus clarki and Potamon dehaani) were examined by Kendall's coefficients of rank correlation. Water depth showed a significant negative correlation with snail density but not with egg density. Depths > 50 cm were likely to reduce both snails and eggs markedly, though neither were significantly correlated with depth. There was no significant correlation with current velocity, although velocities > 50 cm/sec reduced the densities nearly to zero. Both snail and egg densities were positively correlated with COD, indicating that this snail is adapted for more polluted water. Neither density was correlated significantly with the predator fauna. These correlations are discussed with special reference to the life history of the snail in these habitats., Apr. 2000, 46, 46, 78, 84
  • Refereed, Kyushu Plant Protection Research, The Association for Plant Protection of Kyushu, Management of the golden apple snail, Pomacea canaliculata (Lamarck), by drainage and methaldehyde application in direct-sown rice under heavy rainfall conditions., Suzuki Yoshito; Matsumura Masaya; Arimura Kazuhiro; Urano Satoru; Wada Takashi; Yusa Yoichi; Ichinose Katsuya, The effect of a combination of drainage and methaldehyde on feeding damage to directseeded rice by the golden apple snail, Pomacea canaliculata (Lamarck), was tested under conditions of high snail density and heavy rainfall. A 10-day drainage immediately following the wet seeding and subsequent 11-day low-level water management was successful in suppressing the snail damage below an acceptable injury level when methaldehyde granules (10%) were applied at a rate of 4 kg/10 a, 4 days and 10 days after sowing. The analysis of the results of methaldehyde application revealed that the success was due mainly to its effect as feeding arrestant., 2000, 46, 94, 97


  • Not Refereed, 植物防疫, 天敵相を活性化して外来種を制御する:スクミリンゴガイに対する新たな管理法の試み, 遊佐 陽一, 2015, 69, 160, 164
  • Not Refereed, 農林水産省農林水産技術会議事務局研究成果, 超低コスト土地利用型作物生産技術の開発 第6章 暖地2年4作水田輪作地帯 5 暖地二毛作地帯における水田輪作技術の体系化と現地実証(4)忌避材によるスクミリンゴガイの産卵抑制, 田坂幸平; 和田節; 遊佐陽一; 吉田和弘; 安東敏弘; 土屋史紀; 深見公一郎; 佐々木豊, 31 Mar. 2014, 503, 384, 388
  • Not Refereed, bulletin of Kansai Organization for Nature Conservation, Kanasai Organization for Nature Conservation, Temporal change in the distribution of decapod crustaceans prior and posterior to catastrophic flooding by a typhoon in 2011, in three rivers of the Kii Peninsula, western Japan., Tanaka Kaoruko; Hamasaki Kanji; Yamada Makoto; Aoki Misuzu; Yusa Yoichi; Wada Keiji, 2013, 35, 2, 125, 140
  • Not Refereed, 農作業研究, 水路における忌避材によるスクミリンゴガイの産卵抑制, 遊佐 陽一; 田坂幸平; 和田節; 遊佐陽一; 吉田和弘; 安東敏弘; 土屋史紀; 深見公一郎; 佐々木豊, 2013, 48, 133, 141
  • Not Refereed, 日本動物園水族館教育研究会誌, 水族館の飼育生物を利用したフジツボ類の研究, 遊佐 陽一; 山口幸; 金子篤史; 東地拓生; 澤田紘太; 遊佐陽一; 安田恵子; 大和茂之, 2013, 2013, 67
  • Not Refereed, 南紀生物, 南紀生物同好会, On "Uga" specimen of Kumagus MINAKATA, 遊佐 陽一; 大和茂之; 遊佐陽一; 田名瀬英朋, 2012, 54, 1, 1, 4
  • Not Refereed, 九州沖縄農業研究成果情報, スクミリンゴガイ用忌避材と忌避材を利用した産卵抑制技術, 田坂幸平; 佐々木豊; 土屋史紀; 深見公一郎; 遊佐陽一; 安東敏弘, 03 Sep. 2010, 25, 5, 6
  • Not Refereed, 農作業研究, スクミリンゴガイ用忌避材を利用した産卵抑制技術, 田坂幸平; 土屋史紀; 深見公一郎; 佐々木豊; 遊佐陽一; 安東敏弘, May 2010, 45, 1, 2
  • Not Refereed, 植物防疫, 日本植物防疫協会, スクミリンゴガイの特異な性比変動, 遊佐 陽一; 遊佐陽一, 2005, 59, 2, 58, 61
  • Not Refereed, 自然史研究, 水田生態系への侵入者スクミリンゴガイ(ジャンボタニシ)の大和川上・中流域における現状, 遊佐 陽一; 遊佐陽一, 2005, 3, 50, 51
  • Not Refereed, 九州沖縄農業研究センター研究資料, 直播水稲栽培のための大豆作導入によるスクミリンゴガイ密度低減, 遊佐 陽一; 市瀬克也; 和田 節; 遊佐陽一, 2005, 91, 51, 54
  • Not Refereed, 九州農業研究, スクミリンゴガイの越冬:池条件での成長と死亡, 遊佐 陽一; 吉田和弘; 遊佐陽一; 和田 節, 2004, 66, 92
  • Not Refereed, 九州農業研究, スクミリンゴガイに対するコイの捕食能力, 遊佐 陽一; 甲斐伸一郎; 安藤俊二; 塩崎尚美; 遊佐陽一, 2001, 63, 85
  • Not Refereed, Annals of the Sri Lanka Department of Agriculture, Distribution of an alien snail, Pomacea bridgesii, in fresh water habitats and its potential threat to faunal diversity and rice cultivation in Sri Lanka, YUSA Yoichi; Nugaliyadde, L; Jayasundera, D. M; Amarasinghe; A. A. L; Yusa, Y; Hidaka, T, 2001, 3, 375, 376
  • Researches on Population Ecology, Springer-Verlag Tokyo, Density-dependent growth and reproduction of the apple snail, Pomacea canaliculata:a density manipulation experiment in a paddy field, TANAKA Koichi; WATANABE Tomonoari; HIGUCHI Hiroya; MIYAMOTO Kenji; YUSA Yoichi; KIYONAGA Toru; KIYOTA Hirotsugu; SUZUKI Yoshito; WADA Takashi, 01 Dec. 1999, 41, 3, 253, 262
  • Venus : journal of the Malacological Society of Japan, The malacological society of Japan, 22. Evidence for size-dependent allocation in a simultaneous hermaphrodite, the sea hare Aplysia kurodai(Abstracts of Papers Presented at the 2006 Annual Meeting of the Malacological Society of Japan (Tokyo)), Yusa Y., 30 Sep. 2006, 65, 3, 277, 277
  • 日本応用動物昆虫学会大会講演要旨, 日本応用動物昆虫学会, E302 直播水稲における全天候型スクミリンゴガイ管理(防除学・害虫管理・IPM), 鈴木 芳人; 松村 正哉; 有村 一弘; 浦野 知; 和田 節; 遊佐 陽一; 市瀬 克也, 31 Mar. 2001, 45, 94, 94
  • 日本応用動物昆虫学会大会講演要旨, 日本応用動物昆虫学会, E304 大豆転作後水田におけるスクミリンゴガイ密度(防除学・害虫管理・IPM), 和田 節; 市瀬 克也; 遊佐 陽一; 杉浦 直幸, 31 Mar. 2001, 45, 95, 95
  • 日本応用動物昆虫学会大会講演要旨, 日本応用動物昆虫学会, C316 水田内のおけるスクミリンゴガイの生長と増殖(発生予察・被害解析), 鈴木 芳人; 宮本 憲治; 松村 正哉; 有村 一弘; 足達 太郎; 和田 節; 遊佐 陽一; 市瀬 克也; 清田 洋次, 02 Apr. 1999, 43, 70, 70
  • Venus : journal of the Malacological Society of Japan, The malacological society of Japan, Multiple sex-determining genes cause large sex ratio variation in Pomacea canaliculata(Abstracts of Papers Presented at the 2005 Annual Meeting of the Malacological Society of Japan (Nishinomiya)), Yusa Y., 30 Jun. 2005, 64, 1, 81, 81
  • 貝類学雑誌Venus : the Japanese journal of malacology, The malacological society of Japan, 46. Mating behaviour of Pomacea canaliculata : Effects of body size(Abstracts of Papers Presented at the 1998 Annual Meeting of the Malacological Society of Japan at Nagoya City), Yusa Y., 31 Jul. 1998, 57, 2, 151, 151
  • 日本応用動物昆虫学会大会講演要旨, 日本応用動物昆虫学会, J111 水条件・潜土・体サイズ・性がスクミリンゴガイ活動休止個体の長期生存率に及ぼす影響(一般講演), 遊佐 陽一; 和田 節, 01 Mar. 2006, 50, 164, 164

Books etc

  • The Evolution of Sexual Systems, Springer, 2018, Not Refereed
  • The Evolution of Sexual Systems, Springer, 2018, Not Refereed
  • エビ・カニの疑問50, 成山堂, 2017, Not Refereed
  • Global Advances in Ecology and Management of Golden Apple Snails, Philippine Rice Research Institute, 2006, Not Refereed
  • Global Advances in Ecology and Management of Golden Apple Snails, Philippine Rice Research Institute, 2006, Not Refereed


  • 橋添 なな実, 第69回日本生態学会大会, 深海性フジツボ類ミョウガガイ目における繁殖形質の進化, 14 Mar. 2022, 14 Mar. 2022, 19 Mar. 2022
  • 梶本 麻未, 第69回日本生態学会大会, 寄生者フサフクロムシの性決定機構の解明, 14 Mar. 2022, 14 Mar. 2022, 19 Mar. 2022
  • 上原春香; 遊佐陽一, 第 69 回 日本生態学大会, スクミリンゴガイのサイズにおけるハシボソガラスの選好性の地域差異, 14 Mar. 2022
  • 上原 春香; 西山若菜; 和田恵次; 遊佐陽一, 第27回 日本生態学会近畿地区会, 新型コロナウイルスによる人間活動の変化が野生動物の行動に与える影響, 11 Dec. 2021
  • 井口 真実, 2021年度日本生態学会大会近畿地区会, 変態前後の餌量がコノハミドリガイの変態時期と成長に与える影響, 11 Dec. 2021
  • 梶本 麻未, JSTさくらサイエンスプラン, Life cycle and seasonal sex ratio variation in the rhizocephalan Peltogasterella gracilis, 02 Dec. 2021
  • Oral presentation
  • Oral presentation
  • Poster presentation
  • Poster presentation
  • Poster presentation
  • Poster presentation

Research Projects

  • 13 May 2021, 31 Mar. 2023, 21446455, Coinvestigator
  • 18H02494, Coinvestigator
  • 19H03284, Principal investigator
  • 1996, 水生外来動物の管理, 0, 0, 0, Competitive research funding
  • 1996, Management of aquatic invertebrate pests, 0, 0, 0, Competitive research funding
  • 1988, 水生無脊椎生物の生態解明, 0, 0, 0, Competitive research funding
  • 1988, ecological studies on aquatic invertebrates, 0, 0, 0, Competitive research funding
  • フジツボ類の生態, 0, 0, 0, Competitive research funding
  • 有害巻貝の生態に基づく防除, 0, 0, 0, Competitive research funding
  • スクミリンゴガイの防除, 0, 0, 0, Competitive research funding
  • 31 Mar. 2023, Coinvestigator

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