Researcher Profile and Settings

Affiliation

• Faculty of Fisheries Sciences　Marine Bioresource and Environmental Science　Marine Biology and Biodiversity

Job Title

• Assistant Professor

J-Global ID

• 201701016645122601

Research Areas

• Life sciences / Evolutionary biology

Educational Organization

•  Bachelor's degree program　School of Fisheries Sciences
•  Master's degree program　Graduate School of Fisheries Sciences
•  Doctoral (PhD) degree program　Graduate School of Fisheries Sciences

Research Activities

Published Papers

• Interspecific differences of shell utilization pattern of two hermit crab species in southern Hokkaido

  津崎 尚也, 村上 万龍, 石原(安田)千晶, 和田 哲

  Cancer 30 35 - 48 2021/08 [Refereed]
  
• Climbing behavior of guarding males in the hermit crab Pagurus minutus: the effect of rivals, female size, and being weaponless

  Takayoshi Tanaka, Chiaki I. Yasuda, Tsunenori Koga

  Journal of Ethology 0289-0771 2020/11/01 [Refereed]
  
• Does prior residency interact with loss? A study of male–male contests in the hermit crab Pagurus minutus

  Chiaki I. Yasuda, Takehiro Kaida, Tsunenori Koga

  Ethology 126 (6) 660 - 667 0179-1613 2020/06 [Refereed]
  
• Size and sex bias in air-exposure behavior during low tide of the intertidal hermit crab Clibanarius virescens (Krauss, 1843) (Decapoda: Anomura: Diogenidae)

  Akihiro Yoshikawa, Ryutaro Goto, Chiaki I Yasuda, Akira Asakura

  Journal of Crustacean Biology 40 (2) 152 - 155 0278-0372 2020/03/30 [Refereed]
   

  Many species of the hermit crab Clibanarius (Diogenidae) live on rocky shores of tropical and warm temperate regions. Some of these species are known to climb out from tidal pools onto rock surfaces exposed to air during low tide. The ecological significance of this behavior, however, remains unclear. We investigated the differences between air-exposed and non-air-exposed Clibanarius virescens (Krauss, 1843) in relation to their body size, sex, and infestation by three species of parasitic bopyrid isopods. Our generalized additive model (GAM) analyses showed a significant effect of the “smoothing factor” of the interaction between body size and sex for the occurrences of the “air-exposure behavior.” The presence of the ectoparasitic isopods did not affect the air-exposure behavior. Females of C. virescens showed a more distinct trend than in males, whereas air-exposure in both sexes had a peak in approximately 3.0–4.0 mm shield size (comparatively larger size in females, and middle-size in males) and decreased after this size range. Intraspecific and/or interspecific competition for shells may be intense in hermit crabs of this size range because of size overlap, and the individuals that carry suitable shells may avoid such competition by actively escaping from tide pools at low tide.
• Personality differences in white-spotted char fry evident between habitats

  Hasegawa Ryota, Yamada Hiroyuki, Ishihara Chiaki, Wada Satoshi

  Japanese Journal of Ichthyology 一般社団法人 日本魚類学会 67 (1) 11 - 24 0021-5090 2020 [Refereed][Not invited]
   

  Animal personality, defined as consistent individual differences in behavior across time and/or context, has been associated with individual dispersal tendencies in some species. White-spotted char (Salvelinus leucomaenis) populations, often found in above-dam watersheds in Japanese mountain streams, the dams preventing continuous distribution with lower stream reaches, were subject of a behavioral study comparing above-dam and open-stream behavior of fry. Fries were collected from an above-dam area and two open-stream areas within the Kame River system (southern Hokkaido), and personality quantified by measuring a suite of behaviors, such being repeated two-month later. Above-dam fry showed a shorter swimming duration against a novel object and mirror than open-stream fry. The latency time to catch food in above-dam fry tended to be longer than that of the latter. Swimming duration against a novel object and mirror were significantly correlated when data for both groups combined, but not so when data for each group were analyzed independently. These results suggest that personality traits in whitespotted char fry would be shaped by natural selection acting on each habitat, resulting in differing adaptive personality traits.

• Sexual conflict in the hermit crab Pagurus nigrofascia: Female avoidance of male initiation of precopulatory guarding

  Kido Yuina, Iyoda Tomomi, Yasuda Chiaki I., Wada Satoshi

  CANCER 日本甲殻類学会 28 7 - 15 0918-1989 2019/08 [Refereed]
   

  This paper described female guarding avoidance behaviors against precopulatory guarding attempts by males and examines the effect of the number of days until female prenuptial molting on rejection behaviors in the hermit crab Pagurus nigrofascia. We used three types of females in an experiment; (1) ovigerous females (OV–female), (2) females which had not been guarded in the field (NG–female), and (3) females which had been guarded by other males in the field (G–female). We placed a male that had been solitary and a female of either type in a small container, observed the interaction, and compared the female behaviors among the three types of female. The frequencies of retreat and escape from approaching male were highest in OV–females, and lowest in G–females. During male assessment behaviors of females, frequencies of struggle and escape in OV– and G–females were higher than NG–females. 33 of 51 G–females were guarded by males although OV– and NG–females were rarely guarded by males. Many G–females showed rejection behavior during male guarding. However, no significant effect was found in the number of days until the female prenuptial molt on the frequencies of rejection behavior.
• Is the seasonal change of sexual differences in shell use by the hermit crabPagurus minutusconsidered to be driven by growth or reproduction?

  Chiaki I. Yasuda, Yuki Takiya, Masaya Otoda, Reiko Nakano, Tsunenori Koga

  Journal of the Marine Biological Association of the United Kingdom 99 (4) 901 - 910 0025-3154 2019/06 [Refereed]
   

  Abstract Sexual differences in behaviours are often affected by the difference in individual interests between the sexes: growth in males and egg production in females. Some hermit crabs show sexual differences in shell use patterns during the reproductive season. In the non-reproductive season, however, when both sexes are focused on increasing growth, this sexual difference is expected to be reduced. In this study, we compared the pattern of shell use in the hermit crabPagurus minutusbetween seasons, while focusing on the effects of shell shape on growth or egg production. As we predicted, sexual differences in shell use inP. minutusshowed seasonal change. In the non-reproductive season, both sexes appeared to use shells well suited for growth. In the reproductive season, sexual differences became more evident, especially in larger solitary crabs and guarding pairs; males monopolized round-type shells such as those ofUmbonium moniliferum, whereas more than 80% of females relied on high-spiredBatillaria-type shells such as those ofBatillaria zonalis. A lack of advantage for egg number in females usingBatillaria-type shells suggests that female shell use is explained by factors other than maximizing clutch size. Both sexes can moult during the reproductive season, and larger body size is advantageous for reproduction. Given thatBatillaria-type shells resulted in a lower growth increment and males have an advantage in shell fights in congeneric crabs, our findings suggest the importance of intersexual competition for shells and female compromise in determining the seasonal change of shell use patterns inP. minutus.
• Seasonal change in sexual size dimorphism of the major cheliped in the hermit crab Pagurus minutus

  Chiaki I. Yasuda, Masaya Otoda, Reiko Nakano, Yuki Takiya, Tsunenori Koga

  ECOLOGICAL RESEARCH 32 (3) 347 - 357 0912-3814 2017/05 [Refereed][Not invited]
   

  Sexual size dimorphism is a common phenomenon in the animal kingdom, and its seasonal change has been reported in some species that possess traits dimorphic only in males and specialized for male mating success. However, few studies have examined seasonal change in sexual dimorphism of traits possessed by both sexes. Here, we examined the reproductive biology of the hermit crab Pagurus minutus, at a sandflat in the Waka River estuary, Japan, with special reference to seasonal changes in sexual dimorphism of the large claw (major cheliped) size by conducting population and precopulatory guarding-pair sampling. Previous investigation demonstrated that the major cheliped is used as a weapon, and its size, more than body size, determines the winner in male-male contests of this species. We found ovigerous females from November to April, peaking in January, when 80% of females were ovigerous. Sexual size dimorphism of the major cheliped was observed; the degree of dimorphism increased in the reproductive season, when only males possessed an enlarged major cheliped. In addition, in the reproductive season, precopulatory guarding males had a larger body and larger relative size of the major cheliped than did solitary males, although the major cheliped size in guarding males seemed to reach an upper limit. These results suggest that seasonal change in sexual dimorphism of the major cheliped size in P. minutus strongly reflects sexual selection favoring the development of this natural weaponry, and that the degree of the dimorphism might be limited through natural selection.
• Importance of weapon size in all stages of male-male contests in the hermit crab Pagurus minutus

  Chiaki I. Yasuda, Tsunenori Koga

  BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY 70 (12) 2175 - 2183 0340-5443 2016/12 [Refereed][Not invited]
   

  Physical traits such as body size and weapon size typically reflect an individual's resource holding potential (RHP). During male-male contests, contestants use these traits to assess their own and their opponent's RHP. However, the advertisement of RHP does not always predict contest outcome. Here, we examined whether assessment index (body size or weapon size [major cheliped size]) and assessment tactics (self or mutual) are predictors of outcome in male-male contests of the hermit crab Pagurus minutus. In experimental contests over guarded females, intruders did not escalate the contest when their major cheliped was smaller than their opponent's, implying that intruders use mutual assessment based on weapon size when deciding whether to escalate a contest. After escalation, intruders succeeded in taking over females within a shorter period of time with increasing major cheliped size relative to their opponent's. Overall, males with a major cheliped that was larger than their opponent's were more likely to win the contest, although some intruders later stopped guarding the female they had taken over. The importance of relative weapon size after escalation indicates that mutual assessment was also used in this phase of male-male contests. Together, these results suggest that males of P. minutus use mutual assessment based on weapon size throughout male-male contests, and that weapon size is an honest index of RHP. We examined whether assessment index (body or weapon size) and tactics (self or mutual) are predictors of outcome in male-male contests of the hermit crab Pagurus minutus. Intruders did not escalate contests when their major cheliped was smaller than their opponent's, implying that mutual assessment based on weapon size was used to decide whether to escalate contests. After escalation, intruders succeeded in taking over females within a shorter period of time and were more likely to win with increasing weapon size relative to their opponent's. The importance of relative weapon size after escalation indicated that mutual assessment was also used in this phase of contests. Together, these results suggest that males of P. minutus use mutual assessment based on weapon size throughout male-male contests, and that weapon size is an honest index of actual strength.
• Do weaponless males of the hermit crab Pagurus minutus give up contests without escalation? Behavior of intruders that lack their major cheliped in male-male contests

  Chiaki I. Yasuda, Tsunenori Koga

  JOURNAL OF ETHOLOGY 34 (3) 249 - 254 0289-0771 2016/09 [Refereed][Not invited]
   

  In dyadic contests, theoretical studies have predicted that weaker contestants are less likely to engage in fights to minimize the cost of aggression. Since the major cheliped of decapod crustaceans is critically important as a weapon, contestants without a major cheliped should be more likely to give up the contests. We therefore examined whether loss of the major cheliped by the hermit crab Pagurus minutus would affect their decision to escalate male-male contests over guarded females. Intruders without a major cheliped showed no difference in the frequency of escalation compared with intact intruders, and the decision to give up was affected by the body size difference between the contestants. After escalation, compared with intact intruders, intruders without a major cheliped had significantly decreased success of takeover of a female from opponents, suggesting a strong disadvantage of losing their major cheliped. Although the decision of weaponless intruders to escalate seems irrational, several factors, such as poor accuracy of resource holding potential assessment, the influence of body size, and a high benefit to cost ratio of male-male contests, may have affected their behavior.
• Temporal changes in egg number and size during a single breeding season in the hermit crab Pagurus minutus

  NAKANO Reiko, YASUDA Chiaki I., KOGA Tsunenori

  Japanese Journal of Benthology 日本ベントス学会 71 (1) 32 - 36 1345-112X 2016 [Refereed]
   

  The pattern of egg production is important for understanding the reproductive biology in various animals. In species that can spawn multiple clutches during a single reproductive season, egg number and/or size in a population often show temporal changes even within a single season. However, there are only a few studies examining the temporal patterns of egg production in decapod crustaceans including hermit crabs. In this study, we investigated whether the clutch size and egg size change during a single breeding season in the hermit crab Pagurus minutus. We collected precopulatory guarding pairs from December 2014 to April 2015 and recorded the clutch and egg size of the newly spawned eggs. Our results demonstrated that both the clutch size and the egg size varied over this period; fewer and larger-sized eggs were laid in December, whereas eggs laid in February were greater in numbers and smaller in size. Given the temporal changes in environmental conditions in the study area, larvae from the two types of eggs experience different conditions. Former larvae are expected to hatch in February and experience a lower water temperature with relatively poor food conditions, whereas the latter are expected to hatch in April, when the feeding conditions are considered better with relatively warmer water temperatures. The pattern of egg production in this species is thought to vary with the environmental conditions at the time of larval hatching.
• Quality assortative pairing and effect of prior contest outcome on male mate choice in the hermit crab Pagurus nigrofascia

  Kojima Sachi, Yasuda Chiaki I., Wada Satoshi

  CANCER 日本甲殻類学会 25 17 - 24 0918-1989 2016 [Refereed]
   

  In species with both male–male contests and male mate choice, dominance hierarchy in males may affect the male mate choice. This study described patterns of precopulatory guarding pairs of the hermit crab Pagurus nigrofascia in the field to infer variation in male mate choice based on male body size. We found size assortative pairing in precopulatory guarding pairs collected in the field, and that larger males tended to guard females with a shorter time until molting in the field. To examine whether prior outcomes of male–male contests affect male mate choice in P. nigrofascia, we conducted an experiment where a male with a winning or losing experience in male–male contests was placed in a container with two receptive females, and recorded the outcomes of male mate choice. An interaction between two variables of male experiences and time until female molting was statistically significant, indicating that males with a winning experience were likely to choose females with a shorter time until molting while males with losing experience were likely to choose females with longer time until molting. Small inferior males might guard females with low quality as a prudent mate choice in the field.
• Male–male contests in the hermit crab Pagurus filholi: many males do not initiate contests

  Kaga Natsumi, Yasuda Chiaki I., Wada Satoshi

  CANCER 日本甲殻類学会 25 9 - 16 0918-1989 2016 [Refereed]
   

  To examine whether solitary males that had been single in the field are less active in male–male contests than those had been paired in the field in the hermit crab P. filholi, we conducted a laboratory experiment of male–male contests to compare the behaviors of challenger males that had been found not paired in the field (N-male), or had guarded other females in the field (G-male). We introduced a challenger male and a guarding pair into an experimental container and observed the behaviors of challenger males. N-males showed a significantly lower frequency of initiating contests than G-males. Time to initiate contests in N-males was longer than that in G-male. Difference in body size between male contestants significantly affected the time to initiate contests, contest duration and contest outcome, but female quality did not affect these variables. We suggest that solitary males of P. filholi in the field would not be always active for competition for mates, which will decrease intensity of sexual selection in this species.
• Sex-related differences in size, function and regeneration of the major cheliped in the hermit crab Pagurus filholi

  Kento Matsuo, Daisuke Tanikawa, Chiaki I. Yasuda, Satoshi Wada

  MARINE ECOLOGY-AN EVOLUTIONARY PERSPECTIVE 36 (4) 1391 - 1399 0173-9565 2015/12 [Refereed][Not invited]
   

  Pagurus hermit crabs have a well-developed right cheliped (major cheliped) and in some species the major cheliped of males is longer than that of females. This paper describes sex-related differences in major cheliped length and regeneration pattern of the major cheliped in the hermit crab Pagurus filholi. We also examined the function of the major cheliped in male-male competition. Major cheliped length of males was longer than that of females in P. filholi. Males regenerated larger chelipeds than females at the first molt after experimentally induced autotomy. Body size growth in males of the regeneration group was less than that in intact males of the control group while there was no significant difference in body size growth of females between regeneration and control groups. Major cheliped length was included in the best model to explain the outcome of male-male competition and thus sexual selection appears to be a causative factor in the sex-related difference of the major cheliped length. Sex-related differences in the regeneration pattern may reflect differences in evolutionary pressures on males for large major chelipeds and females for large body size.
• Reason for being single: some males do not guard receptive females in the hermit crab Pagurus filholi

  Yukari Hasaba, Chiaki I. Yasuda, Satoshi Wada

  ANIMAL BEHAVIOUR 107 1 - 5 0003-3472 2015/09 [Refereed][Not invited]
   

  In animals that reproduce sexually, males are often under strong selection to maximize the number of mating opportunities. However, in some iteroparous species, males do not always maximize the allocation of time and energy to the present mating opportunity. Male hermit crabs of the genus Pagurus show precopulatory guarding as a mate acquisition strategy. Although almost all males within this genus guard and compete for receptive females, males of Pagurus filholi differ in how likely they are to do so. To examine the factors explaining the absence of guarding behaviour in P. filholi, a laboratory experiment was conducted that focused on whether either of two receptive females was guarded by solitary males that had been found not paired in the field, had lost a previous male-male contest or had copulated with other females. Solitary males showed a significantly lower frequency of guarding than males with experience of losing or of copulation. In the solitary group, males that moulted within 5 days after the experimental trial did not guard females, and the moulting frequency of nonguarding males was significantly higher than that of guarding males. In further analysis, smaller solitary males were shown to be less likely to guard females. The results of the experiment suggest that males of P. filholi may not always invest as much as possible in the present mating opportunity but may temporarily invest in growth during the 8-month mating season. (C) 2015 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
• Previous mating experience increases fighting success during male-male contests in the hermit crab Pagurus nigrofascia

  Chiaki I. Yasuda, Kento Matsuo, Satoshi Wada

  BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY 69 (8) 1287 - 1292 0340-5443 2015/08 [Refereed][Not invited]
   

  Prior social experience often affects subsequent competitive interactions and their outcomes. Although the effects of prior contest experience have been widely examined, effects of mating experience remain less well examined. We examined, in males of the hermit crab Pagurus nigrofascia, whether males successively copulated with more than one female and whether males with copulation experience differed in their subsequent contest behaviors and probability of winning in male-male contests compared to males without copulation experience. The copulation experience of intruders was manipulated and the contest behaviors compared between mated and unmated groups. Males mated with several females regardless of the male body size. Compared with unmated intruders, intruders with mating experience succeeded more often in taking over females and did so within a shorter period particularly when the male-male contests occurred over females with a long time to molt. These results suggest that mated males of P. nigrofascia overestimate the female quality and/or enhance the competitive performance similar to the "winner effect" that is a positive feedback from prior winning experience to future contests.
• Regeneration of major cheliped after the mating season in the hermit crab Pagurus middendorffii

  Chiaki I. Yasuda, Satoshi Wada

  Crustacean Research 日本甲殻類学会 44 29 - 38 0287-3478 2015 [Refereed][Not invited]
   

  Males of the hermit crab Pagurus middendorffii use their major cheliped in male–male contests during the reproductive season. This study examined whether autotomized major chelipeds were regenerated before, during or after the mating season. We reared males that were experimentally induced to autotomize just before the mating season (October). During the mating season (November), few males molted even if they had autotomized their major cheliped. In contrast, males initiated a molt at the end of and after the mating season, and most of the autotomized males regenerated their major cheliped before the end of the rearing period (December). This suggests that regenerated major chelipeds in this study affect events other than mating, particularly perhaps future shell acquisition associated with general activities such as predator avoidance, physiological tolerance and growth.
• Hermit crab, Pagurus middendorffii, males avoid the escalation of contests with familiar winners

  Chiaki I. Yasuda, Kento Matsuo, Yukari Hasaba, Satoshi Wada

  ANIMAL BEHAVIOUR 96 49 - 57 0003-3472 2014/10 [Refereed][Not invited]
   

  Prior contest outcomes often affect subsequent contest behaviour (winner/loser effects). If contestants discriminate between familiar and unfamiliar opponents, individual recognition may alter the strength and/or manner of winner/loser effects. We examined whether hermit crabs, Pagurus middendorffii, changed their contest behaviour based on winner/loser effects, whether they distinguished a familiar opponent from an unfamiliar opponent, and how the familiarity with the opponent related to the winner/loser effects in male-male contests. Males of this species show precopulatory guarding behaviour, and male-male contests often occur between a guarding male and an intruder. In contests between unfamiliar males, intruders use self-assessment during the initial contact phase and mutual assessment during the physical combat phase to determine their behaviours. Precopulatory guarding males and females collected in the field were used in two consecutive trials of male-male contests. Losers in the first trial were used as focal intruders in the second trial with (1) a familiar opponent that had won the first trial, (2) an unfamiliar opponent that had won the first trial with another intruder, or (3) a naive opponent with no trial experience. Focal intruders did not alter their aggressiveness against either unfamiliar or naive opponents in the second trial. However, they rarely initiated physical combat against familiar opponents in the second trial. When they initiated combat, they gave up sooner against familiar opponents than against unfamiliar opponents. These results suggest that intruders are able to distinguish familiar opponents from others and decrease their aggressiveness only when they encounter familiar opponents. Our study therefore shows loser effects in P. middendorffii related to the familiarity with the opponent and suggests intruders can obtain information about their opponents during the initial encounter. (C) 2014 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
• Sexual size dimorphism in two endemic hermit crabs, Pagurus traversi and P. novizealandiae, in New Zealand

  Satoshi Wada, Chiaki I. Yasuda, Colin McLay

  Bulletin of Fisheries Sciences, Hokkaido University 北海道大学大学院水産科学研究科編集出版委員会 64 (2) 31 - 35 1346-1842 2014 [Not refereed][Not invited]
   

  The evolutionary factors of sexual size dimorphism and reproductive characters in Pagurus traversi and P. novizealandiae,are discussed. Investigations and sample collection were conducted in the intertidal area around Kaikoura peninsula, southernisland of New Zealand from 22 February to 23 March 2012. The number of crabs collected was 1198 P. traversi and 318 P.novizealandiae. The degree of size dimorphism ((mean male size)/(mean female size)) was 1.09 and 1.03 in P. traversi and P.novizealandiae, respectively. The fecundity relationship between clutch size and female body size (shield length, mm) in P. traversiwas estimated as log10[clutch size] =1.010 + 0.794 × log10[female size3], indicating that clutch size approximately increaseas an isometric relationship. All males guarded females smaller than themselves in nine precopulatory guarding pairs of P.traversi. However, difference in the mean size between the guarding males (4.79 mm) and other males (4.50 mm) was small(0.29), suggesting that large size advantage might be weak in mate acquisition compared with other species of the genus Pagurus. Weak evolutionary selection pressure acting on male body size may explain relatively small degree of sexual size dimorphism inP. traversi.
• Rapid regeneration of the major cheliped in relation to its function in male-male contests in the hermit crab Pagurus middendorffii

  Chiaki I. Yasuda, Kento Matsuo, Satoshi Wada

  Plankton and Benthos Research 9 (2) 122 - 131 1882-627X 2014 [Refereed][Not invited]
   

  Most crustaceans are known to regenerate their appendages after losing them, and the pattern of regeneration may be related to its function. The pattern of regeneration of the right major cheliped was examined after experimentally induced autotomy and its behavioral function during male-male contests for mates was investigated in the hermit crab Pagurus middendorffii. Males with an autotomized major cheliped regenerated it at the first molt after autotomy and showed smaller growth in body size than in control males. The shape of the regenerated cheliped was more slender than the original, implying that the regenerated major cheliped would be less robust and weaker than previously. The length of the major cheliped of an owner male (guarding a female at the start of a dyadic contest) and the body size of an intruder affected whether or not the contest escalated, but the major cheliped length of the intruder and the body size of the owner determined the outcome of the escalated contest. The intruder used the major cheliped as an offensive weapon to take the female away from the owner by force after the contest escalated. The owner often moved the major cheliped forward, similar to a fencing weapon, before escalation. Such movement of the owner seems to be effective to prevent the intruders from approaching, and the regenerated cheliped of the owner may not require much robustness and strength as a defensive weapon before escalation. Rapid regeneration of the major cheliped in P. middendorffii would therefore be beneficial to minimize the disadvantages incurred by loss of the major cheliped.
• Effect of cheliped loss due to autotomy on shell selection behavior in the hermit crab Pagurus middendorffii

  Kento Matsuo, Chiaki I. Yasuda, Satoshi Wada

  Crustacean Research 日本甲殻類学会 43 (43) 41 - 46 0287-3478 2014 [Refereed][Not invited]
   

  Major cheliped is used in shell selection in the hermit crab Pagurus middendorffii. This study examined how loss of the major cheliped due to autotomy affected shell selection behavior and whether shell-size preference was affected. Crabs after autotomy changed shells less frequently than intact crabs. However, there was not a significant difference in shellsize preference between autotomized crabs and intact crabs. Since autotomy occurs during fleeing from a predatory attack in the field, subsequent reduction of frequency of changing shells might suppress the risk of predation for crabs.
• Male mate choice and male-male competition in the hermit crab Pagurus nigrofascia: importance of female quality

  Yutaro Suzuki, Chiaki Yasuda, Fumio Takeshita, Satoshi Wada

  MARINE BIOLOGY 159 (9) 1991 - 1996 0025-3162 2012/09 [Refereed][Not invited]
   

  Male mate choice has recently been reported in some animals with male-male competition. In the laboratory, we examined whether males choose their mates based on female quality that was indicated by body size and/or days to prenuptial molt, and the effects of female quality on male-male competition in the hermit crab Pagurus nigrofascia. We collected samples from April to May 2009 at an intertidal shore in Hokkaido, Japan (41A degrees N, 140A degrees E). When a male simultaneously encountered two receptive females in the mate choice experiment, males chose females which require less time to molt. When a male guarding a female with less time to molt was challenged by an intruder, the guarding male defended the female for a longer period and was more likely to win the contest. These results indicate that male P. nigrofascia use time to molt to discriminate between females.
• Assessment strategy in male-male contests of the hermit crab Pagurus middendorffii

  Chiaki Yasuda, Fumio Takeshita, Satoshi Wada

  ANIMAL BEHAVIOUR 84 (2) 385 - 390 0003-3472 2012/08 [Refereed][Not invited]
   

  Assessment of their own resource-holding potential (RHP) and that of their opponent affects the behaviours individuals use in contest competition. Contestants may use their own RHP and/or the relative RHP of opponents to make decisions and may switch these two assessment tactics during fighting. In male-male contests of hermit crabs Pagurus middendorffii, we examined whether contestants switch assessment tactics and whether they assess body size or major cheliped size as an index of RHP. Males of this species show precopulatory guarding behaviour, and male-male contests often occur when males guarding females encounter intruder males. We conducted trials of dyadic contests to investigate the assessment tactics in two phases of the contest: initial and combat. Intruders gave up the contest without escalating to physical combat when they were smaller. When physical combat occurred, it lasted longer if the difference in size of the major cheliped between guarding males and intruders was small, and males with a larger major cheliped than the opponent had a higher probability of winning the contests. These results suggest that P. middendorffii uses its own body size during the initial phase of a contest and relative major cheliped size during the combat phase to assess RHP. (C) 2012 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
• Effects of male size and mate quality on male-male contest in the hermit crab Pagurus filholi

  Tanikawa, D, C. Yasuda, Y. Suzuki, S. Wada

  Japanese Journal of Benthology 日本ベントス学会 67 (1) 15 - 19 1345-112X 2012 [Refereed][Not invited]
   

  Males of the hermit crab Pagurus filholi guard females until spawning, and male-male contest often occur when guarding males encounter other males. A contest comprises two phases, initial contact and physical combat, and larger males typically win. We conducted male-male contest experiments to examine whether body sizes of both sexes of P. filholi and female receptivity affect whether and when a contest escalates to physical combat, as well as contest duration and outcome. For each experimental trial, a pair, comprising a “pairing male” and a “pairing female”, and a second male (“intruder”) were placed into a small container, and their behaviors were observed for 15 minutes. Each intruder had been guarding a female in the field but we removed this female (“removed female”) just before the trial. All pairs in the field were reconstructed each after trial to quantify female receptivity. This was done by checking each female for spawning every day. As an index of size, we measured shield length (length of calcified anterior portion of cephalothorax) of all crabs. In the trials, large size of the intruder and high receptivity of the removed female significantly shortened the time until the onset of physical combat. Intruders needed more time to take over the pairing females and were less likely to win the contests when the intruders were small, the pairing males were large, and the removed females were large. Body size and receptivity of the pairing female had no effect on the process and the outcome of male-male contest. These results suggest that a male P. filholi can assess the quality of female it is guarding and remember its assessment for at least a short period. Asymmetry between contestants in this memory store for female quality could affect the process and the outcome of male-male contests in P. filholi.
  Contents of supplementary materials: Appendix 1: Explanation of movie files, Mov 1: Male-male contest, Mov 2: Cessation of male contest, Mov 3: No guarding after takeover.
• Function of the major cheliped in male-male competition in the hermit crab Pagurus nigrofascia

  Chiaki Yasuda, Yutaro Suzuki, Satoshi Wada

  MARINE BIOLOGY 158 (10) 2327 - 2334 0025-3162 2011/10 [Refereed][Not invited]
   

  Functions of the major cheliped in pagurid hermit crabs have been studied in fights for shells. The major cheliped often shows sexual size dimorphism, suggesting that sexual selection favors the development of the male major cheliped. The function of the major cheliped in male-male competition was examined in Pagurus nigrofascia collected from April to June 2009 on the intertidal rocky shore in southern Hokkaido, Japan (41 degrees N, 140 degrees E). Sexual size dimorphism of the major cheliped was observed, and precopulatory guarding males had larger major chelipeds than solitary ones. Guarding males used the major cheliped to deter intruders during competitive interactions. Males without a major cheliped were disadvantaged even if they were larger than opponents and had ownership. Cheliped size affected the outcomes of contests between similar sized males. This suggests that the male major cheliped in P. nigrofascia protects mates from competitors and, consequently, enhances male mating success. Sexual selection may favor the development of the major cheliped in male pagurids.

Books etc

• ＜北水ブックス＞ ヤドカリに愛着はあるが愛情はない

  石原千晶 (Single work)
  海文堂出版 2022/08 (ISBN: 9784303800086)

MISC

• Precopulatory guarding in hermit crabs: what information do crustaceans use in decision making?

  和田哲, 守田安祐美, 石原(安田)千晶  海洋と生物  40-  (1)  106‐113  -113  2018/02/15  [Not refereed][Not invited]
  
• 研究活動の敷居：ヤドカリと出会い，この道に進むまで

  石原(安田) 千晶  日本水産学会誌  84-  (4)  764  -764  2018  [Not refereed][Not invited]
  
• Regeneration of major cheliped after the mating season in the hermit crab Pagurus middendorffii

  I. Yasuda Chiaki, Wada Satoshi  CANCER  27-  (0)  1  -5  2018  [Not refereed][Not invited]
  
• 宿貝となる巻き貝サイズに依存したヤドカリサイズの違い:和歌山県の加太と友ヶ島における比較

  塩崎祐斗, 寺島杏奈, 石原(安田)千晶, 古賀庸憲  南紀生物  58-  (1)  48‐51  2016/06/30  [Not refereed][Not invited]
  
• Pre- and Post-molting behaviors in the barnacle, Balanus rostratus

  Tamechika Masami, Yasuda Chiaki I, Wada Satoshi  CANCER  25-  (0)  25  -27  2016  [Not refereed][Not invited]
  
• Autotomy of the major cheliped as the anti-predatory behavior in the hermit crab Pagurus middendorffii

  Matsuo Kento, Yasuda Chiaki I, Wada Satoshi  CANCER  24-  (0)  21  -23  2015  [Not refereed][Not invited]
  
• Male-male competition and the role of large cheliped in the hermit crab Pagurus nigrofascia

  YASUDA Chiaki, SUZUKI Yutaro, WADA Satoshi  日本甲殻類学会大会講演要旨集  47th-  45  2009  [Not refereed][Not invited]
  

Awards & Honors

• 2017/09 日本甲殻類学会 Excellent Paper Award
   Regeneration of major cheliped after the mating season in the hermit crab Pagurus middendorffii. 

  受賞者: 石原千晶;和田哲
• 2017/09 日本ベントス学会 日本ベントス学会奨励賞
   

  受賞者: 石原(安田)千晶
• 2016 日本動物行動学会 Editor's Choice Award
   Do weaponless males of the hermit crab Pagurus minutus give up contests without escalation? Behavior of intruders that lack their major cheliped in male-male contests 

  受賞者: Chiaki I. Yasuda;Tsunenori Koga

Research Grants & Projects

• 知性の源流を探る「認知進化生態学」研究の総括と推進支援

  日本学術振興会：科学研究費助成事業

  Date (from‐to) : 2023/04 -2026/03 

  Author : 高橋 宏司, 安房田 智司, 幸田 正典, 佐藤 成祥, 石原 千晶
• 社会があれば知性はあるか：甲殻類・水圏無脊椎動物の社会と認知能力を捉え直す

  日本学術振興会：科学研究費助成事業

  Date (from‐to) : 2023/04 -2026/03 

  Author : 石原 千晶, 竹下 文雄, 三浦 収, 磯村 尚子
• ヤドカリに探る個体識別の継続と破棄更新

  日本学術振興会：科学研究費助成事業

  Date (from‐to) : 2021/04 -2024/03 

  Author : 石原 千晶

   

  本研究は、申請者がオス間闘争を介した個体識別能力を実証したテナガホンヤドカリを対象として (i) 強度の低い小競り合いにおける基本的な識別記憶時間の特定、 (ii) オス間闘争、あるいは小競り合いにおける識別時と現在の不一致による影響、という２つの課題に取り組み、本種を含むヤドカリ類を認知能力研究の新たなモデル生物として提案することを目的としている。 2021年度は（i）のデータ解析に着手した段階で、産前産後休暇及び育児休暇を取得しており、年度の大部分において研究活動を実施していない。そのため、現在も解析を継続中である。ただし、休暇取得以前に解析したデータを検討したところ、先行研究で用いられていた基準では本種の行動を精査することが困難である可能性が示唆された。よって、次年度以降に行動基準を再検討する必要性が生じている。
• Individual recognition of hermit crabs

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2017/04 -2021/03 

  Author : Yasuda Chiaki

   

  In this study, I aimed to overcome the delusion that advanced cognitive abilities can only occur in vertebrates with advanced brain nervous systems, and used the brainless hermit crab Pagurus middendorffii as a model organism to examine the cognitive abilities of invertebrates. During male-male contests for a female, inferior smaller males of this species show individual recognition to identify larger males that have once defeated them and avoid a second fight at least one hour. However, the smaller males actively fight again if the same opponent has lost his major cheliped, a weapon trait. This suggests that males of this species are capable of discarding previously constructed individual recognition and updating the information quickly.

Educational Activities

Teaching Experience