Research activity information

• Sep. 2017, 日本甲殻類学会, Excellent Paper Award
  Regeneration of major cheliped after the mating season in the hermit crab Pagurus middendorffii.
  石原千晶;和田哲
• Sep. 2017, 日本ベントス学会, 日本ベントス学会奨励賞
  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
  Chiaki I. Yasuda;Tsunenori Koga

• Dear enemy phenomenon in fiddler crabs: escalation of fights with unfamiliar individuals rather than familiar neighbours
  Fumio Takeshita; Chiaki I. Yasuda
  Animal Behaviour, 233, 123470, 123470, Elsevier BV, Mar. 2026, [Peer-reviewed], [Last author]
  Scientific journal, 44554023
• Sexual differences in seasonal changes in major cheliped size and use pattern during dyadic interactions in the hermit crab <i>Pagurus filholi</i>
  Tomomi Iyoda; Yuina Kido; Chiaki I Yasuda; Satoshi Wada
  Plankton and Benthos Research, 20, 4, 231, 240, The Plankton Society of Japan/The Japanese Association of Benthology, 26 Nov. 2025, [Peer-reviewed], [Corresponding author]
  Scientific journal, 45265778
• Is an individual recognition immutable? Subordinate hermit crabs fight with a familiar but weaponless dominant
  Chiaki I. Yasuda
  Journal of Ethology, Springer Science and Business Media LLC, 09 Sep. 2025, [Peer-reviewed], [Lead author, Corresponding author]
  English, Scientific journal, 45085704;45265778;44554023
• Aggression, but Not Familiar Recognition, Occurs During Cohabitation in Females of a Hermit Crab
  Haruka Kudo; Chiaki I. Yasuda
  Ethology, Wiley, 21 Jul. 2025, [Peer-reviewed], [Last author, Corresponding author]
  English, Scientific journal, ABSTRACT
  
  Aggressive interactions are ubiquitous in the animal kingdom and are a key context favoring the evolution of familiar recognition. This cognitive ability has been widely reported in male crustaceans, including Pagurus hermit crabs. However, our understanding of female–female aggression and female cognitive ability remains relatively limited. Here, we describe the pattern of intrasexual aggression and assess the presence of familiar recognition in females of the hermit crab Pagurus middendorffii through two consecutive trials with 1‐day's cohabitation. In the first trial, pairs of similar‐sized females typically engaged in aggression using their appendages, though shell fights were rare. Following a 1‐day's cohabitation, in the second trial, female behaviors did not differ between familiar (previously paired) females and unfamiliar (newly paired) females. As familiar recognition is beneficial in avoiding the associated costs of aggression, the lower frequency of energetically costly shell fights might explain the lack of evidence for familiar recognition in female P. middendorffii, as the benefits of recognizing opponents in such less intense interactions may be limited., 44554023
• Is an individual recognition immutable? Subordinate hermit crabs fight with a familiar but weaponless dominant
  Chiaki I. Yasuda
  bioRxiv, Cold Spring Harbor Laboratory, 18 May 2025, [Lead author, Corresponding author]
  English, Abstract
  
  Individual recognition can help subordinates avoid contests with lower success against familiar dominant opponents. This holds true in crustaceans, but if the dominants autotomize their weapon (chela/cheliped) before a second encounter, there is a decrease of potential fighting ability in the prior dominant and an increased chance of success in the prior subordinates than before. I examined whether familiar recognition is still effective even when subordinates encounter a familiar, but temporarily weaponless, dominant through two consecutive trials of male–male contests in the hermit crabPagurus middendorffii. SubordinateP. middendorffiiintruders avoid fights with a familiar dominant guarder. After establishing hierarchy and familiarity between subordinates and dominants possessing a weapon (major cheliped), the subordinates encountered the same dominants after experimentally induced autotomy of the weapon. Subordinate intruders actively fought with the familiar but weaponless guarders. This result might be explained by the subordinate’s updating information; that is, opponents were recognized the same but weaker than before. Information updating could be a useful new line of investigation into cognitive ability in invertebrates., 45265778;45085704
• Use of Social Information About Novel Food by Juvenile Solitary Forktongue Goby, Chaenogobius annularis
  Daisuke Nakayama; Chiaki I. Yasuda; Satoshi Wada
  Ethology, 131, 7, Wiley, 28 Apr. 2025, [Peer-reviewed], [Corresponding author]
  English, Scientific journal, ABSTRACT
  
  Animals use various forms of information to reduce uncertainty about the environment and make adaptive decisions. They can acquire information directly from the environment (personal information) or by observing other individuals' behavior (social information). Since young animals in particular may benefit from acquiring social information owing to their lack of experience at this stage, social information in juveniles would be important even in solitary species. This possibility has, however, been less studied in juvenile solitary fishes. We examined whether juveniles of the solitary forktongue goby, Chaenogobius annularis, use social information about novel artificial food (fish‐food flakes) and a novel food location (water surface). We first tested whether feeding on the novel food is facilitated by past experience to confirm that C. annularis juveniles could learn this information: compared with naïve juveniles, juveniles that previously experienced the novel food showed significantly shorter latencies to begin feeding (at the surface or underwater, hereafter first feeding), and to feed on the water's surface (hereafter, surface feeding). We then compared feeding on novel food between naïve juveniles paired with an experienced juvenile and those paired with a naïve juvenile. Naïve juveniles paired with an experienced juvenile fed significantly more frequently and sooner in both first and surface feedings than the randomly chosen naïve juveniles in each naïve pair. These results suggest that C. annularis juveniles use social information to learn about food and that social information use by juveniles is widespread among vertebrates, regardless of their sociality., 44554023
• Morphometric changes at terminal molt and reproductive capacity in the kelp crab Pugettia ferox Ohtsuchi & Kawamura, 2019 (Decapoda: Brachyura: Majoidea)
  Aiko Fukasawa; Chiaki I Yasuda
  Journal of Crustacean Biology, 44, 2, Oxford University Press (OUP), 01 Jun. 2024, [Peer-reviewed], [Last author]
  Scientific journal, Abstract
  
  It has been assumed that functional maturity and terminal molt occur simultaneously in majoid crabs. Although this assumption seems to be accurate in females, males of some majoids can mate with females even before their terminal molt. Here we describe the morphometric changes at terminal molt and test the reproductive capacity of pre-terminal molt males in the kelp crab Pugettia feroxOhtsuchi & Kawamura, 2019 (Majoidea, Epialtidae, Epialtinae). We measured the post-pseudorostral carapace length (PCL), claw length (CL), claw height (CH), and pleon (abdomen) width (AW) of crabs to estimate the morphological features distinguishing pre- and post-terminal molt individuals, namely relative claw length (CL/PCL) ≥ 0.660 in males and relative abdominal width (AW/PCL) ≥ 0.487 in females. Males with pre-terminal molt morphological features were observed for behavioral maturity through encounters with mature virgin females under laboratory conditions. More than half of the males copulated with a female and then underwent terminal molt. These females bred clutches, and larvae hatched. These results indicate that pre-terminal molt males of P. ferox can be functionally mature.
• Male Pagurus minutus hermit crabs use multiple types of information in decisions to give up male–male contests
  Chiaki I. Yasuda; Tsunenori Koga
  Scientific Reports, 13, 1, Springer Science and Business Media LLC, 24 Nov. 2023, [Peer-reviewed], [Lead author, Corresponding author]
  Scientific journal, Abstract
  
  Organisms use information to make adaptive decisions in various contexts, including aggression. Potentially weaker, but better-informed, contestants should give up earlier to reduce fighting costs by using information related to their own lower success such as their size relative to their opponent and past contest outcomes to make this choice. Here, we examined whether intruders of the hermit crabPagurus minutuscould use information about their (1) smaller size, (2) past contest defeats, (3) opponent’s past wins, or (4) relationship in the dominance hierarchy to their opponent when making a decision to give up during male–male contests for a female. In all trials, we randomly matched a smaller intruder with a larger opponent that was guarding a female. Our analyses suggest thatP. minutusintruders can use all four types of information to decide whether to give up a contest without escalation or decrease its duration after escalation; it is the first species ofPagurusreported to do so, and the second reported to be able to distinguish familiar opponents from others in the context of male–male contests. These findings demonstrate the importance of cognitive abilities in minimizing costs when competing for vital resources., 45265778;44554023
• 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, Aug. 2021, [Peer-reviewed], [Corresponding author]
  Japanese, Scientific journal
• 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, Springer Science and Business Media LLC, 01 Nov. 2020, [Peer-reviewed], [Corresponding author]
  Scientific journal
• 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, Wiley, Jun. 2020, [Peer-reviewed], [Lead author, Corresponding author]
  Scientific journal
• 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, Oxford University Press (OUP), 30 Mar. 2020, [Peer-reviewed]
  Scientific journal,
  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, 67, 1, 11, 24, The Ichthyological Society of Japan, 2020, [Peer-reviewed]
  Japanese,

  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, 28, 7, 15, Carcinological Society of Japan, Aug. 2019, [Peer-reviewed]
  Japanese, 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, Cambridge University Press (CUP), Jun. 2019, [Peer-reviewed], [Lead author, Corresponding author]
  Scientific journal, 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, May 2017, [Peer-reviewed], [Lead author, Corresponding author]
  English, Scientific journal
• 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, Dec. 2016, [Peer-reviewed], [Lead author, Corresponding author]
  English, Scientific journal
• 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, Sep. 2016, [Peer-reviewed], [Lead author, Corresponding author]
  English, Scientific journal
• 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, 71, 1, 32, 36, JAPANESE ASSOCIATION OF BENTHOLOGY, 2016, [Peer-reviewed], [Corresponding author]
  Japanese, 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, 25, 17, 24, Carcinological Society of Japan, 2016, [Peer-reviewed]
  Japanese, 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, 25, 9, 16, Carcinological Society of Japan, 2016, [Peer-reviewed]
  Japanese, 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, Dec. 2015, [Peer-reviewed]
  English, Scientific journal
• 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, Sep. 2015, [Peer-reviewed]
  English, Scientific journal
• 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, Aug. 2015, [Peer-reviewed], [Lead author, Corresponding author]
  English, Scientific journal
• Regeneration of major cheliped after the mating season in the hermit crab Pagurus middendorffii
  Chiaki I. Yasuda; Satoshi Wada
  Crustacean Research, 44, 29, 38, Carcinological Society of Japan, 2015, [Peer-reviewed]
  English, Scientific journal, 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, Oct. 2014, [Peer-reviewed], [Lead author, Corresponding author]
  English, Scientific journal
• 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, Plankton Society of Japan, 2014, [Peer-reviewed], [Lead author, Corresponding author]
  English, Scientific journal
• 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, 43, 43, 41, 46, The Carcinological Society of Japan, 2014, [Peer-reviewed]
  English, Scientific journal, 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, Sep. 2012, [Peer-reviewed]
  English, Scientific journal
• Assessment strategy in male-male contests of the hermit crab Pagurus middendorffii
  Chiaki Yasuda; Fumio Takeshita; Satoshi Wada
  ANIMAL BEHAVIOUR, 84, 2, 385, 390, Aug. 2012, [Peer-reviewed], [Lead author, Corresponding author]
  English, Scientific journal
• 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, 67, 1, 15, 19, JAPANESE ASSOCIATION OF BENTHOLOGY, 2012, [Peer-reviewed]
  Japanese, Scientific journal, 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, Oct. 2011, [Peer-reviewed], [Lead author, Corresponding author]
  English, Scientific journal

• Function of Bubble for Recovery from Cryptobiosis in Tardigrade Milnesium tardigradum
  Masahiro Ise; Toshikuni Nakatani; Chiaki I. Yasuda, Bulletin of Fisheries Sciences, Hokkaido University, 74, 1, 1, 11, Aug. 2024, [Last author]
• 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, 15 Feb. 2018
  生物研究社, Japanese
• 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
  公益社団法人 日本水産学会, Japanese
• 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
  Carcinological Society of Japan, Japanese
• 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, 30 Jun. 2016
  Japanese
• Pre- and Post-molting behaviors in the barnacle, Balanus rostratus
  Tamechika Masami; Yasuda Chiaki I; Wada Satoshi, CANCER, 25, 0, 25, 27, 2016
  日本甲殻類学会, Japanese
• 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
  Carcinological Society of Japan, Japanese
• 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
  English

• 今すぐ見つけに行きたくなるヤドカリ探索図鑑
  でんか, コラム「ヤドカリのオスたちの闘いを見つめる」、pp. 176-179
  緑書房, 08 Aug. 2025, 4868110276, 216, [Contributor]
• ＜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
  海文堂出版, Aug. 2022, 9784303800086, [Single work]

• ヤドカリの社会を覗く －３つの駆け引き－
  石原千晶
  北斗市高齢者大学, Sep. 2025, Japanese, Public discourse
  [Invited]
• ヤドカリと歩む ～主流“じゃない”研究も面白い～
  石原千晶
  第56回 道南支部理科研究発表大会, 12 Sep. 2023, Japanese, Public discourse
  [Invited]
• 第4回「ヤドカリ入門：貝殻に潜む “駆け引き” 上手たち」
  石原千晶
  2023北海道大学水産学部 公開講座「海をまるごとサイエンス！」, 07 Aug. 2023, Japanese, Public discourse
  [Invited]

• 海洋生物学特論Ⅱ, 2024年, 修士課程, 水産科学院
• Introduction to Fisheries Sciences Ⅱ（水産科学汎論Ⅱ）, 2024年, 修士課程, 水産科学院
• 大学院共通授業科目（一般科目）：自然科学・応用科学, 2024年, 修士課程, 大学院共通科目
• 海洋生物科学実験Ⅱ, 2024年, 学士課程, 水産学部
• 水圏生物学, 2024年, 学士課程, 水産学部
• 水圏生物科学実習, 2024年, 学士課程, 水産学部
• 海洋保全学, 2024年, 学士課程, 水産学部
• 海洋生物科学実験Ⅰ, 2024年, 学士課程, 水産学部
• ベントス学, 2024年, 学士課程, 水産学部
• 野外巡検, 2024年, 学士課程, 水産学部

• 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
  科学研究費助成事業
  01 Apr. 2023 - 31 Mar. 2026
  高橋 宏司; 安房田 智司; 幸田 正典; 佐藤 成祥; 石原 千晶
  日本学術振興会, 学術変革領域研究(B), 京都大学, 23H03867
• 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
  科学研究費助成事業
  01 Apr. 2023 - 31 Mar. 2026
  石原 千晶; 竹下 文雄; 三浦 収; 磯村 尚子
  日本学術振興会, 学術変革領域研究(B), 北海道大学, 23H03870
• ヤドカリに探る個体識別の継続と破棄更新
  科学研究費助成事業
  01 Apr. 2021 - 31 Mar. 2024
  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。
  日本学術振興会, 若手研究, 北海道大学, 21K15159
• Individual recognition of hermit crabs
  Grants-in-Aid for Scientific Research
  01 Apr. 2017 - 31 Mar. 2021
  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.
  Japan Society for the Promotion of Science, Grant-in-Aid for Young Scientists (B), Hokkaido University, 17K15188

• Aug. 2025
  ギョギョッとサカナスター ヤドカリの仲間たち
  テレビ番組監修
• May 2023
  【ヤドカリの飼い方】飼育グッズや注意点を陸棲・水棲別に分けて紹介
  Web記事監修（https://magazine.cainz.com/article/101323）