Faculty Profiles - KOGA Tsunenori

Published Papers - KOGA Tsunenori

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Shell abandonment by a hermit crab is an effective antipredator behavior against a portunid crab

M. Harada, K. Yoshino, T. Koga （Part： Last author,　Corresponding author )

Journal of Zoology ( Wiley ) 326 16 - 22 2025.01 [Refereed]

Abstract

When hermit crabs recognize the risk of predation, they generally hide inside their shells or flee from the area, and little is known about their escape behaviors after being captured by a predator. We discovered that the hermit crab Pagurus filholi abandons its shell and attempts to flee when captured by the predatory crab Charybdis japonica, and we examined the effectiveness of this behavior in laboratory experiments. We fed captive C. japonica with P. filholi occupying gastropod shells. When the C. japonica could not break the shell even a little, it gave up and the P. filholi neither abandoned its shell nor was eaten. However, when the predator succeeded in partially breaking the shell, the hermit crab often abandoned the shell, and when it did so, it often survived. Once the predator had completely broken the shell open (implying that the shell has been broken to the extent that it no longer has any structural integrity), all hermit crabs that remained back in the shell (22/22) were consumed, and those that abandoned the shell were also often consumed (3/5). Therefore, hermit crabs do not need to abandon their shells if a predator is unable to break the shell even slightly, but if a predator begins to break the shell, they have a better chance of survival if they abandon their shells at an early stage.

Spatial changes in the macrozoobenthic community structure at 27 tidal flats from the Sanriku coast to the Yatsushiro Sea, Japan, using citizen-based monitoring data

Gen KANAYA, Hajime ITOH, Taeko KIMURA, Misuzu AOKI, Takeshi YUHARA, Masanori TARU, Tomoo UNAGAMI, Hiroyuki YOKOOKA, Naohiko SAKATA, Tsunenori KOGA, Teruki MASUMOTO, Keisuke MORI, Takao SUZUKI, Jotaro URABE, Kosaku YOKOYAMA

Japanese Journal of Benthology ( The Japanese Association of Benthology ) 78 ( 1 ) 61 - 72 2023.12 [Refereed]

Male Pagurus minutus hermit crabs use multiple types of information in decisions to give up male–male contests

Yasuda CI, Koga T

Scientific Reports 13 2323 2023.11 [Refereed]

Anti-predator responses to chemical, visual, and combined cues by an estuarine hermit crab from sandy tidal flats

YamamotoY, Yoshino K, Koga T （Part： Last author )

Behavioral Ecology and Sociobiology ( Springer Science and Business Media LLC ) 77 ( 6 ) 2023.05 [Refereed]

Climbing behavior of guarding males in the hermit crab Pagurus minutus: the effect of rivals, female size, and being weaponless

Tanaka T, Yasuda C I, Koga T （Part： Last author )

Journal of Ethology ( Springer Science and Business Media LLC ) 39 ( 1 ) 115 - 123 2021.01 [Refereed]

Practical Report of a New Teacher-Trainig-Course Subject 'Teaching Method of Time for Integrated Learning': Lesson Content and Questionnaire Results

Osamu TANIJIRI, Toshihide KISHI, Makiko KAJIMURA, Tsunenori KOGA

和歌山大学教職大学院紀要：学校教育実践研究 6 21 - 31 2021 [Refereed]

Predation intensity of the portunid crabs <b><i>Charybdis japonica</i></b> and <b><i>Portunus pelagicus</i></b> on the hermit crab <b><i>Diogenes nitidimanus</i></b> according to season, predator size, and prey shell type and size

Naohiko SAKATA, Kenji YOSHINO, Tsunenori KOGA （Part： Last author,　Corresponding author )

Japanese Journal of Benthology ( The Japanese Association of Benthology ) 75 ( 0 ) 35 - 42 2020.12 [Refereed]

Does prior residency interact with loss? A study of male-male contests in the hermit crab Pagurus minutus

Yasuda CI, Kaida T, Koga T

Ethology ( Wiley Blackwell ) 126 660 - 667 2020.05 [Refereed]

Is the seasonal change of sexual differences in shell use by the hermit crab Pagurus minutus considered to be driven by growth or reproduction?

Yasuda CI, Takiya Y, Otoda M, Nakano R, Koga T （Part： Last author )

J Mar Biol Assoc UK ( Cambridge University Press (CUP) ) 99 ( 4 ) 901 - 910 2019 [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.

田辺湾の干潟生物の変遷：環境省モニタリングサイト1000干潟調査より

古賀庸憲, 青木美鈴, 香田唯, 渡部哲也（Part： Lead author,　Corresponding author )

地域自然誌と保全 40 ( 1 ) 129 - 141 2018 [Refereed]

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 （Part： Last author )

ECOLOGICAL RESEARCH ( SPRINGER JAPAN KK ) 32 ( 3 ) 347 - 357 2017.05 [Refereed]

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.

Population ecology of the hermit crab Clibanarius infraspinatus in the Waka River

宮川直明, 古賀庸憲（Part： Corresponding author )

日本ベントス学会誌 ( 日本ベントス学会編集委員会 ) 71 ( 2 ) 70 - 77 2017 [Refereed]

双眼実体顕微鏡を用いたクマムシ観察の授業実践

梶村麻紀子, 寺本由, 廣瀬正紀, 岩田勝哉, 古賀庸憲, 荒木良一, 高須英樹

和歌山大学教職大学院紀要 2 179 - 184 2017 [Refereed]

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 ( SPRINGER ) 70 ( 12 ) 2175 - 2183 2016.12 [Refereed]

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 ( SPRINGER JAPAN KK ) 34 ( 3 ) 249 - 254 2016.09 [Refereed]

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.

Size differences of the hermit crabs depending on the size of gastropod shells between Kada and Tomogashima in the Wakayama prefecture

Shiozaki Y, Terashima A, Yasuda CI, Koga T

Nankiseibutu 58 48 - 51 2016.06

Fighting with an unreliable weapon: opponent choice and risk avoidance in fiddler crab contests

Daisuke Muramatsu, Tsunenori Koga

BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY ( SPRINGER ) 70 ( 5 ) 713 - 724 2016.05 [Refereed]

Current signaling theories predict that animal signals are generally honest, but each signaling system allows some admixture of deception. Male fiddler crabs fight aggressively through use of their greatly enlarged major claw, which grows on the left or right side. Some males have fragile regenerated claws (regenerated males) and others have robust original claws (original males), but crabs cannot visually discriminate between the two types. In the present study, we conducted field observations in a population of Uca lactea to investigate how regenerated males fight with their inferior weapons, and how other males deal with the potential deception. Regenerated males employed bluffing tactics; they pretended to be aggressive to deter opponents, but surrendered when the fight escalated. Regenerated males tended to choose smaller and opposite-handed opponents, probably because claws can be grappled tightly in same-handed fights. The bluffing tactics seemed to be partially successful, because regenerated males were not selectively challenged by other males and defeated original males in 41.7 % of the cases. However, original males developed counter-bluff tactics, such as choosing same-handed opponents and persisting in contests even when the opponent was larger. Consequently, original males defeated regenerated males equipped with longer a claw in 42.9 % of the cases. In the most striking case, an original male evicted a resident male from his burrow despite the 42.7 % longer regenerated claw. This counter-bluff tactic decreases the reliance on the signal of strength (weapon size) and limits the benefit of bluffing.
Male fiddler crab (Uca lactea) fight with their major claw, which grows on either the left or right side. However, males with fragile a regenerated claw (regenerated males) which were similar in size to an original claw made deception in the fights. Regenerated males employed bluffing tactics; they behaved aggressively to deter opponents, but surrendered when the fight escalated. They chose smaller and opposite-handed opponents, because claws can be grappled tightly in same-handed fights. As a result, they defeated males with an original claw (original males) in 41.7 % of the cases. Interestingly, however, original males developed a counter-bluff tactic: they chose same-handed opponents and persisted in contests even when the opponent was larger. Consequently, 42.9 % of original males defeated regenerated males equipped with a larger claw. This counter-bluff tactic serves to "call the bluff" and limit the benefits of bluffing.

Temporal changes in egg number and size during a single breeding season in the hermit crab Pagurus minutus

中野玲子, 石原(安田)千晶, 古賀庸憲

日本ベントス学会誌 ( 日本ベントス学会誌編集委員会 ) 71 ( 1 ) 32 - 36 2016 [Refereed]

ADAPTATION IN A PERIPHERAL HABITAT: INTRASPECIFIC VARIATION IN OSMOREGULATORY TRAITS IN AN ESTUARINE HERMIT CRAB (PAGURUS MINUTUS)

Kenji Yoshino, Tsunenori Koga, Koichi Taniguchi, Rei Tasaka

JOURNAL OF SHELLFISH RESEARCH ( NATL SHELLFISHERIES ASSOC ) 33 ( 1 ) 53 - 59 2014.04 [Refereed]

We investigated osmoregulatory ability of Pagurus minutus from three sites on the Waka River estuary (upper reach, river mouth, and middle). The sites have different salinity regimes and we tested whether crabs were adapted to their site locally or whether they showed phenotypic plasticity. The upper reach had a low salinity (similar to 16) during low tide, unlike the other two sites (similar to 28-31). The exposure of crabs from each site to seven different salinity levels (0-52.5) showed that P. minutus is a hyper-hypo-osmoregulator at all sites and is able to survive in 8.75-52.5 salinity levels for 24 h. Crabs from the upper reach, however, maintained greater hemolymph osmolarity in diluted media, and most of them were able to survive in even 0 salinity medium for 24 h. Crabs from the other two sites were not able to tolerate this condition and all died. Another experiment, involving a 1-wk acclimation to 5 decreasing salinity media (35 to 0), showed that the survival was about 1.3 times greater for crabs from the upper reach than from the other two sites. Because the crab density of the upper reach was significantly less than that of the other two sites, the upper reach is a marginal habitat established by asymmetrical larval dispersal from central saline habitats. Nevertheless, no crab from the saline sites survived exposure to the salinity of zero medium. These results suggest that the high osmoregulatory ability of crabs from the upper reach of the estuary does not represent a local adaptation; crabs acquire it after dispersal through developmental plasticity.

Resource value differentially affects fighting success between reproductive and non-reproductive seasons

Zakea Sultana, Junko Takaoka, Tsunenori Koga （Part： Last author )

JOURNAL OF ETHOLOGY ( SPRINGER JAPAN KK ) 31 ( 2 ) 203 - 209 2013.05 [Refereed]

Inter-male competition for resources is usually studied during species' reproductive seasons because fighting is common and conspicuous, but how this competition compares with that during the non-reproductive season is rarely investigated. Here, we compared competition for burrows between the reproductive and non-reproductive seasons in a mud crab. We conducted two natural and three experimental observations: Under natural conditions, we observed fights between residents and intruders in (1) reproductive and (2) non-reproductive seasons, and found similar results in both seasons; two factors, body size difference and residency, contributed equally to fight outcomes; (3) During the reproductive season we created an intruder by capturing a resident male and placing him in the burrow of another resident to induce a fight; (4) We repeated this but first placed a female in the burrow before introducing the intruder; findings for both experiments were similar to those for natural fights; (5) During the non-reproductive season, we repeated the third experiment and found a different result: fight outcome was determined by the difference in body size, not residency. This is the first study to show that differing subjective value of a resource between the reproductive and non-reproductive seasons affects fight outcomes.

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