Faculty Profiles - KOGA Tsunenori

Published Papers - KOGA Tsunenori

Division display >> ／ All the affair displays1 - 64 of about 64

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.

DOI

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]

DOI

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]

DOI

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]

DOI

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]

DOI

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]

DOI

Predation intensity of the portunid crabs Charybdis japonica and Portunus pelagicus on the hermit crab Diogenes nitidimanus 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]

DOI

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]

DOI

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.

DOI

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.

DOI

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]

DOI

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.

DOI

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.

DOI

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.

DOI

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]

DOI

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.

DOI

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.

DOI

Macrobenthic fauna in a tidal flat estuary of the Arida River, Wakayama Prefecture, central Japan: a report of the results of the civil procedurefor researching benthos in 2010 and 2011.

Murase Atsunobu, Yuhara Takeshi, Kato Kenji, Koga Tsunenori

bulletin of Kansai Organization for Nature Conservation ( Kanasai Organization for Nature Conservation ) 34 ( 1 ) 45 - 51 2012

Chelipeds are the real weapon: cheliped size is a more effective determinant than body size in male-male competition for mates in a hermit crab

Kenji Yoshino, Tsunenori Koga, Sayaka Oki

BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY ( SPRINGER ) 65 ( 9 ) 1825 - 1832 2011.09 [Refereed]

To understand the evolution of weapons, we must understand both their functions and relative importance compared to body size in determining fighting success. Many decapod crustaceans develop disproportionately large chelipeds for their body size and use them as a weapon in agonistic interaction. There are, however, examples where weapons are merely signals of resource holding potential (RHP) and the RHP is actually determined by body size. We investigated the function and relative efficacy of body size and major cheliped size in male-male contests for females in the hermit crab Diogenes nitidimanus. Contests over females took two forms: (1) males preemptively guarded females and opponents did not fight with the guarding male. Cheliped size contributed significantly to the settlement of these contests and probably functioned as a visual signal for the opponents. (2) Guarding males engaged in physical combat with an opponent. In these cases, both body and cheliped sizes affected contest outcomes. The effect size for cheliped size was as strong, or stronger, than that for body size. These results suggest that large chelipeds have evolved as a true weapon and are effective in escalated fights for resources. Therefore they are also efficient visual signals for settling contests with only display. Our results are a rare example that clearly demonstrate that weapons are a more important determinant of fights than body size when both body and weapon size affect resource acquisition.

DOI

Population fluctuations of the endangered brackish-water snail Iravadia (Fairbankia) sakaguchii (Gastropoda, Iravadiidae) fro, 2000 to 2010 in the Waka River Estuary, middle Japan

WADA Keiji, OHATA Mari, KOGA Tsunenori

Japanese Journal of Benthology ( JAPANESE ASSOCIATION OF BENTHOLOGY ) 66 ( 1 ) 22 - 25 2011 [Refereed]

The abundance and size structure of a population of an endangered brackish-water snail, Iravadia (Fairbankia) sakaguchii, was surveyed annually in August and September in the Waka River Estuary, Wakayama, middle Japan. The number of snails at the three surveyed stations, comprising a total area of ca. 9.5 m2, was greatest in 2000 (1738 snails) and decreased in most successive years to 2009 (7 snails), but increased slightly in 2003 and again in 2010 (27 snails). Few or no small-sized snails were present in any year, which suggests that little or no recruitment of planktonic larvae was taking place. When the population density increased, large-sized snails were responsible, reflecting the immigration of snails from other nearby populations. This phenomenon indicates the importance of maintaining a patchy population distribution for the conservation of this species.

DOI

Temporal changes in the reproductive population structures and males' secondary sexual character of the hermit crab Diogenes nitidimanus

Tsunenori Koga, Kenji Yoshino, Yuri Fukuda （Part： Lead author,　Corresponding author )

ECOLOGICAL RESEARCH ( SPRINGER TOKYO ) 25 ( 5 ) 1007 - 1017 2010.09 [Refereed]

We investigated the reproductive ecology of D. nitidimanus in the Waka-River estuary with special reference to temporal change in the relative size of chelae length for males, i.e., secondary sexual character. Ovigerous females were observed from April to October, peaking in June-July with over 90% of females being ovigerous. Adult female carapace size ranged from 3.5 to 8.5 mm, but with the majority of females falling between 5-6 mm. Male carapace length was more evenly distributed between 3.5 and 10 mm. Juvenile settlement occurred mostly in July, during which time the frequency of both large females (over 6.5 mm in carapace length) and large males (over 8.5 mm in carapace length) clearly decreased. The carapace length of precopulatory-guarded females varied from 4.8 to 8.0 mm, while guarding males were almost over 7 mm and always larger than their paired females. The relative growth of the major chelae differed significantly between small and large males during the early months of the year, including the reproductive peak months (April-June). During these early months, large males had relatively larger chelae for their body size than did small crabs. This difference, however, was not evident later in the year (July-September). Large males may grow their chelae relatively long in the early months in order to take advantage of the mating opportunities during April-June. This is the first report in animals, to our knowledge, that relative size of the secondary sexual character for males temporarily change during a single reproductive season.

DOI

Perceived predation risk and mate defense jointly alter the outcome of territorial fights

Tsunenori Koga, Satoshi Ikeda

BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY ( SPRINGER ) 64 ( 5 ) 827 - 833 2010.04 [Refereed]

Virtually all animal conflicts occur over access to mates or resources that affect survival, the two key components of fitness. In this paper, we report that predation risk and mate defense jointly affect the outcomes of contests between male sand crabs (Scopimera globosa) for burrows in which crabs mate and take shelter from predators. We observed the contests under three different conditions: (1) the natural condition of low predation risk and without the presence of a female; (2) the first experiment in which we imposed upon only intruding males the perception of predation risk-by digging them from their burrows, capturing and handling them, and placing them into other males' burrows-to increase the value of the burrows for the intruders as shelter, and (3) the second experiment in which we repeated this treatment but increased the resource value of the burrow to the resident by placing a female in his burrow. The difference in body size between contestants was the main determinant of victory in all analyses. However, perceived predation risk also partly affected the outcomes of the fights: The motivated intruders were likely to win even when they were a little smaller than the residents. In addition, defense of a female had a significant effect on the outcomes of fights: The motivated residents won more fights than the motivated intruders, indicating that these two treatments caused asymmetric increases of the resource value. This is the first report of two external factors simultaneously raising resource value, affecting motivation of contestants, and altering the outcome of fights.

DOI

Practice of the civil procedure for reserching benthos inhabiting tidal flats at the estuary of Arida River,Wakayama Prefecture.

Nakagawa Masahiro, Yuhara Takeshi, Suzuki Takao, Koga Tsunenori

関西自然保護機構会誌 ( Kanasai Organization for Nature Conservation ) 32 ( 2 ) 131 - 140 2010

Green tide formed by free-floating Ulva spp. at Yatsu tidal flat, Japan

Tohru Yabe, Yuichi Ishii, Yoshimasa Amano, Tsunenori Koga, Seiji Hayashi, Seiichi Nohara, Hideki Tatsumoto

LIMNOLOGY ( SPRINGER TOKYO ) 10 ( 3 ) 239 - 245 2009.12 [Refereed]

Green tides at Yatsu tidal flat, Tokyo Bay, Japan, were first reported in 1995 and formed by a bloom only of free-floating Ulva species. On the tidal flat, the bloom area in well-developed periods increased after 1995 and covered 27.1 ha in May 2002. Based on vertical aerial photographs, green tide remaining in winter during 1996-2007 covered 4.7 ha when first observed in 1999 and increased to 17.5 ha in January 2002 thereafter. We found that the expansion of green tide was related to such factors as an increase in Kira's Warmth Index, a decrease in annual cumulative hourly air temperatures below 7 degrees C in December, an increase in salinity, and unintentional introduction of Ulva ohnoi. We also found that green tide at Yatsu tidal flat occurred in the course of the improvement of water quality.

DOI

A trematode infection with no effect on reproductive success of a sand-bubbler crab

Tsunenori Koga

ECOLOGICAL RESEARCH ( SPRINGER TOKYO ) 23 ( 3 ) 557 - 563 2008.05 [Refereed]

The infection effects of the parasitic digenean trematode on the body weight and reproductive success of the sand-bubbler crab were examined. Gynaecotyla squatarolae (Trematoda: Microphallidae) infects the body cavity of Scopimera globosa (Decapoda: Scopimeridae) and uses the crab as its second intermediate host. The parasites infected all reproductive crabs examined to varying degrees. Larger crabs of both sexes had more parasites than smaller ones, probably because body size reflects age, and older crabs had a longer period of exposure to infection. Males had more parasites than females, probably because of sexual difference in acting time on the surface. Ovigerous females stay in closed burrows and do not act on the surface during incubation, and so have less chance of infection than males. The quantity of infecting parasites did not explain variations in either body weight or reproductive success of individual crabs in a field experiment. The life history of this parasite, relative body size of the crabs, and cost and the possible benefit of manipulation for the parasite may explain these results.

DOI

Distribution of three hermit crab species in the Waka-River Estuary (in Japanese with English Summary)

Tsunenori KOGA, Yuri FUKUDA

Japanese Journal of Benthology ( JAPANESE ASSOCIATION OF BENTHOLOGY ) 63 23 - 29 2008 [Refereed]

In Japan, the hermit crabs Pagurus minutus, Diogenes nitidimanus and Clibanarius infraspinatus are common in inner bays, sandy tidal flats and shallow subtidal sediment, respectively. We investigated the distribution of these three species in summer at six sampling sites in the Waka-River Estuary, Wakayama Prefecture, Japan. The sampling sites were placed along the length of the estuary, with Site 1 situated high up in the brackish water of the estuary, Site 6 at the river mouth, and the other four sites at intermediate locations along the estuary gradient with the number of each site. Pagurus minutus was the dominant species at five out of six sites. Diogenes nitidimanus was mainly found at intermediate St. 3 and 5, relatively close to the river mouth, and had sandy substrates. Clibanarius infraspinatus was mostly found at St. 6. The sex ratio of D. nitidimanus was highly biased to males at St. 3 and to females at St. 5, while the sex ratio of the other two species did not vary across sites except for P. minutus at St. 4. Carapace and chelae length of males were larger than those of females in P. minutus for their right hands and in D. nitidimanus for their left hands, but not in C. infraspinatus for their right hands. In D. nitidimanus, small males were especially abundant at St. 3, while males of various size including large ones, were collected at St. 5. Females of various sizes were found at both sites. However, there were very few females at St. 3, while many females, including ovigerous ones, inhabited St. 5. The existence of the small male population distant from the reproductive population in D. nitidimanus may be an interesting aspect with respect to the life history strategy of the males and deserves further investigation.

DOI

佐賀県七浦干潟公園で採集された稀少な二枚貝類２種

古賀庸憲, 山下博由, 佐竹潔, 矢部徹（Part： Lead author )

ユリヤガイ 10 ( 1/2 ) 1 - 6 2008 [Refereed]

カニ類における配偶行動と繁殖戦略・性淘汰・捕食−被食関係. （総説）

古賀庸憲

日本生態学会誌 57 ( 1 ) 1 - 12 2007 [Refereed]

DOI

和歌川河口干潟におけるチュウシャクシギNumenius phaerpusの採餌行動

上野公輔, 古賀庸憲

和歌山大学教育学部紀要 ( 56 ) 21 - 26 2006

Waving display by male Scopimera globosa (Brachyura : Ocypodoidea) as courtship behavior

M Ohata, K Wada, T Koga

JOURNAL OF CRUSTACEAN BIOLOGY ( CRUSTACEAN SOC ) 25 ( 4 ) 637 - 639 2005.11 [Refereed]

Male sand-bubbler crabs Scopimera globosa perform a waving display during their reproductive season, but waving is not used when a male is paired with a female. A male grasps and brings a female into his burrow for mating. We conducted this study to clarify the function of the waving display of S. globosa. The frequency of waving was correlated with male size, and males that paired successfully underground waved significantly more often and were significantly larger than their,neighbors. Females that were released in front of waving males either approached or fled from the waving male or they made no response. All the females that approached waving males completed underground pairing without resisting capture by the male, but most females that fled or did not respond resisted capture. Females that approached waving males had more developed ovaries compared to females that fled. These results suggest that waving in S. globosa functions as pan of courtship behavior and that waving males detect females with ripe gonads according to how the female responds to the displaying male.

自由集会「生物多様性科学の統合をめざして」に参加して(<特集1>生物多様性科学の統合をめざして)

古賀庸憲

日本生態学会誌 ( 一般社団法人日本生態学会 ) 55 ( 2 ) 316 - 318 2005

DOI

マクロベントス相から見た干潟タイプ及び，種の豊富さ・現存量・多様度指数・絶滅危惧種による干潟評価

保全生態学研究 10(1): 45-55 2005 [Refereed]

和歌山市の干潟に棲息するカニ類5種における二生吸虫類被嚢幼虫の寄生状況

信貴真啓, 古賀庸憲, 木船悌嗣

南紀生物 ( 南紀生物同好会 ) 47(1): 33-36 ( 1 ) 33 - 36 2005

和歌川河口干潟におけるウミニナ科３種とフトヘナタリ科２種の分布とサイズ組成．

松浦聖子, 古賀庸憲

南紀生物 ( 南紀生物同好会 ) 46 (2): 85-91 ( 2 ) 85 - 91 2003

Evaluation of an organic matter decomposing function from hydrolytic enzyme activities of tidal flat sediments in Japan

Mikiya Hiroki, Tohru Yabe, Seiichi Nohara, Hirokatsu Utagawa, Kiyoshi Satake, Tsunenori Koga, Ryuhei Ueno, Masanobu Kawachi, Makoto M. Watanabe

Japanese Journal of Limnology ( Japanese Society of Limnology ) 64 ( 2 ) 113 - 120 2003 [Refereed]

Thirteen study site of tidal flats were selected from 5 areas in Japan (east Hokkaido, Tokyo Bay, Ise Bay, Ariake -kai and Yaeyama Islands) to evaluate an organic matter-decomposing function from the hydrolytic enzyme activities of sediments. At each study site, sediment samples were collected from layers 0 - 10 cm in depth, and cellulase (CEL) and β-acetylglucosaminidase (AGA) activities were measured using CMCNa and PNAG, respectively, as substrates. The enzymic activities were different among the study sites
CEL ranged 2 - 30 nmol g-1 h-1 and AGA ranged 10 - 140 nmol g-1 h-1. There were positive correlationships between the two enzymic activities, with both activities also showing positive correlations with organic matter contents and silt-clay contents. AGA activity was relatively higher at sites where the biomass of crustaceans was higher. These results show that enzymic activities seem to change quantitatively and qualitatively with the organisms supply detritus and with silt-clay content that affects the stability of the enzymes. Due to enzymic activity, the decomposing function was higher in tidal flats where organic-matter and silt-clay content were high.

DOI

和歌川河口干潟で採集されたウモレマメガニPseudopinnixa carinata (Ortmann, 1894) （カクレガニ科）．

古賀庸憲

南紀生物 46 (2): 145-146 145 - 146 2003

The assessment of female reproductive state during courtship and scramble competition in the fiddler crab, Uca paradussumieri

M Murai, T Koga, HS Yong

BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY ( SPRINGER ) 52 ( 2 ) 137 - 142 2002.07 [Refereed]

Male fiddler crabs, Uca paradussumieri, mate underground during a 4- to 7-day period each full and new moon. As soon as the tide recedes, males enter the burrows of females that will ovulate the following day ('pre-ovigerous' females). Males copulate with and guard these females until they ovulate. When interrupted by an intruding male, the first male to reach the female is usually able to defend her and successfully mate with her. In fiddler crabs, females mate multiply and there is last male sperm precedence. Before each semi-lunar mating period, male U. paradussumieri were more likely to court females with whom they would later mate than other nearby females with whom they did not mate. This suggests that males collect information on female reproductive state prior to the females becoming ovigerous. In this species, aggression was common between males that courted the same female. When previously courted females were approached by other males, the initial courter attempted to forcefully disrupt the courtship. This behavior may allow males the exclusive use of information on female reproductive condition. It also suggests a type of scramble competition between males over females. Furthermore, it indicates that males are able to locate receptive females prior to their becoming ovigerous. The shorter guarding period observed in this species, as compared with other fiddler crabs, is caused by females rejecting longer guarding periods. Male ability to assess female reproductive status may therefore be advantageous because it increases male mating success within a scramble type of competitive polygyny.

DOI

Parasite and Species Richness : Association of Scopimera globosa (Crustacea: Decapoda: Ocypodidae), Batillaria cumingi (Mollusca: Gastropoda: Potamididae) and Gynaecotyla squatarolae (Trematoda: Digenea: Microphallidae)

KOGA Tsunenori

Japanese journal of benthology ( 日本ベントス学会誌編集委員会 ) 57 67 - 70 2002 [Refereed]

DOI

Functional Assessment for Restoration of Intertidal Sandy and Muddy Flat Ecosystems(<SPECIAL ISSUE> Restoration of Ecosystems)

YABE Tohru, NOHARA Seiichi, UTAGAWA Hirokatsu, SATAKE Kiyoshi, HIROKI Mikiya, UENO Ryuhei, KAWACHI Masanobu, WATANABE Makoto, KOGA Tsunenori

Landscape Research Japan Online ( The Japanese Institute of Landscape Architecture ) 65 ( 4 ) 286 - 289 2002 [Refereed]

The restoration of the wetland ecosystems is an essential problem in the world, however, the evaluation technique for the functions of ecosystems, especially in the intertidal wetlands, has not been established still in spite of the ecosystems adjoining with the human life. The Functions of a wetland tend to roughly correspond with characteristics of both the water and sediments of the wetland. In this study, the 13 intertidal sandy and muddy flat wetlands were selected from Hokkaido to Okinawa, and the indicators for water and sediments were investigated as a first step of the functional ecosystem assessment in Japan. The classification for traditional landform subclass, i.e. fore-beach, estuary and lagoon, was unclearly changeable, and it often did not agree with the functional classification. In the intertidal sandy and muddy flat wetlands in Japan, the subclass for HGM Approach should be set corresponding to the characteristics of influent water and sediments, and it was considered that the ecosystem evaluation should be carried out in each Hydrogeomorphic Unit classified at smaller-scale than the original HGM Approach in U.S..

DOI

Male-biased predation of a fiddler crab

T Koga, PRY Backwell, JH Christy, M Murai, E Kasuya

ANIMAL BEHAVIOUR ( ACADEMIC PRESS LTD ) 62 ( 2 ) 201 - 207 2001.08 [Refereed]

Great-tailed grackles, Quiscalus mexicanus, prey on fiddler crabs, Uca beebei, either by running straight at them or by running past them then angling sharply back to strike. Grackles that used angled runs caught only males and were twice as successful as birds that used straight runs and caught equal numbers of males and females. Why do grackles that use angled runs catch only males? Males were not differentially available, nor did grackles prefer them to females in choice tests. Fewer crabs entered their burrows when we moved a model predator past them than when we moved it directly towards them and crabs allowed the model to get closer when it passed then returned to strike. Although crabs may take more risks when birds use angled runs, the sexes did not differ in their escape responses. Hence, differential risk taking cannot explain male-biased predation by birds using angled runs. We suggest that males, with their large claws and lighter colours, are more conspicuous than cryptic females. When a bird runs past then turns to dash back at a crab it may be able to keep track of a male much better than a female. Indeed, grackles missed all females they struck at using angled runs. Hence, males may be conspicuous and preferred prey to birds using angled runs. Males' enlarged claws, bright colours and other sexually selected traits may increase male predation rate in this context. (C) 2001 The Association for the Study of Animal Behaviour.

DOI

千葉県の東京湾沿岸部と和歌山県和歌川河口干潟で得られたコメツギガニに寄生するMicrophallidae（扁形動物門：吸虫綱）の被嚢幼虫について。（共著）

木船悌嗣, 古賀庸憲

長崎県生物学会誌 ( 長崎県生物学会 ) 53, 50-53 ( 53 ) 50 - 53 2001

On the metacercariae of three species of the genus Maritrema (Trematoda: Microphallidae) found in Scopimera globosa inhabiting on three main islands of the Ryukyus

Transactions of the Nagasaki Biological Society (53): 12-16 2001

Burrow defense behaviors in a sand-bubbler crab: Scopimera globosa, in relation to body size and prior, residence

M Takahashi, N Suzuki, T Koga

JOURNAL OF ETHOLOGY ( JAPAN ETHOL SOC ) 19 ( 2 ) 93 - 96 2001 [Refereed]

The burrow defense behaviors in a sand-bubbler crab, Scopimera globosa, living on a tidal flat, were experimentally examined. Body size and prior residence influenced the results of struggles for the burrows, and large individuals or the burrow owners won in most cases when the intruders were not significantly larger than the owners. Most large owners defended their burrows by directly fighting their opponents. On the other hand, small owners defended their burrows in three different ways. (1) Owners fought directly against same-sized or smaller intruders. For larger intruders, (2) most owners returned to their burrows when the owner was nearer to the burrow than the intruder (returning behavior), and (3) owners sat motionless when the intruder was nearer to the burrow than the owner (sitting behavior). Success ratios of the three types of burrow defense were 38.2%, 88.5%, and 100%, respectively, It was considered that sitting behavior of the cryptically colored S. globosa has evolved because intruders cannot see motionless owners and consequently cannot detect the owner's burrow.

DOI

南西諸島のコメツキガニに寄生するMaritrema属（吸虫綱：Microphallidae）の嚢幼虫３種について。（共著）

木船悌嗣, 古賀庸憲

長崎県生物学会誌 ( 長崎県生物学会 ) 53, 12-16 ( 53 ) 12 - 16 2001

Underground mating in the fiddler crab Uca tetragonon: the association between female life history traits and male mating tactics

T Koga, M Murai, S Goshima, S Poovachiranon

JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY ( ELSEVIER SCIENCE BV ) 248 ( 1 ) 35 - 52 2000.05

Brood size and other life-history traits of females affect male investment in mating. Female Uca tetragonon, producing relatively small broods, were attracted to the burrows of males for underground mating (UM) while carrying eggs, Most UM females released larvae and ovulated new broods during the pairing, averaging 3.9 days. While a female was incubating one brood, another brood was developing within the ovaries because the females were feeding adequately during incubation. These findings suggest that in U. tetragonon, a small-brood species, females increase the total number of broods produced by breeding continually. In contrast, in large-brood species, feeding by ovigerous females is relatively brief and not enough to prepare the next brood during incubation, inducing temporal separation between incubation and brood production. Unlike females in other ocypodids where females with large broods remain in thr breeding burrows of males, most female U. tetragonon left the male after UM. Wandering in female U. tetragonon after the pairs separate may occur because their small broods are adequately protected by an abdominal flap. Relative brood size probably determines the vulnerability of the incubated broods to the females' surface behavior. Hence, male reproductive success in large-brood species may decrease greatly if males expel their mates after ovulation, although this is not necessarily so in small-brood species. Whether the male drives away the female or not may depend on which behavior within tither small- or large-brood species yields the greater male reproductive success. In U. tetragonon some females extruded eggs in their own burrows after surface mating as well as in males' burrows after UM. It was unclear whether females chose a male with a larger burrow as an UR I mate unlike several large-brood species. Burrows of both UM males and ovigerous females in U. tetragonon were relatively smaller than those in some large-brood species, indicating that incubation of small broods does not require large burrows. Rather than benefits of UM by female choice, wandering resulting from intersexual conflict, and sperm competition may explain why some females mate in males' burrows in this small-brood species. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI

Male-male competition and intersexual interactions in underground mating of the fiddler crab Uca paradussumieri

T Koga, M Murai, HS Yong

BEHAVIOUR ( BRILL ACADEMIC PUBLISHERS ) 136 651 - 667 1999.06

We investigated inter-male competition for female mates and intersexual interactions in underground mating (UM) of the fiddler crab Uca paradussumieri. Males search for and then enter the burrows of females that are ready to ovulate ('pre-ovigerous'). In order to ensure their paternity, these males guard the female until she ovulates the following day. Thereafter the male leaves. Intruding male conspecifics attempt to reach the female. Guarding males either fight with them (N = 27), or use the flat-claw defence (N = 96) in which the male stands in the burrow shaft and blocks the entrance with his enlarged claw. The flat-claw was a very successful defence tactic (93% success), even when the intruder was larger than the guarding male. Pre-ovigerous females accepted the first male to enter her burrow, suggesting that female mate choice does not occur. Though males that succeeded to enter the burrow of pre-ovigerous female were larger than males that failed to do so, males that succeeded UM were not larger than males that failed UM. Males that succeeded UM by a take-over were not larger than either the males that were defeated or the males that succeeded in UM after their first entering. Early localization of pre-ovigerous females was important in male mating success, as was a male's ability to defend the female before she ovulated. However, some females that were not pre-ovigerous were guarded forcibly for 2 days by males that had failed to pair with a pre-ovigerous female that day. Prolonged guarding was less successful for males than guarding for one day, probably because the males had to fight with more intruders. Ln addition, prolonged guarding may not be adaptive for females because they lose feeding time and mate with males that lack competitive abilities.

Metacercaria of Microphalloides japonicus (Digenea : Microphallidae) found in Ilyoplax pusilla (Decapoda : Ocypodidae) on the seashore of the eastern part of Fukuoka City, Kyushu, Japan(共著)

Transactions of the Nagasaki Biological Society 50 5 - 8 1999

「福岡市東部沿岸産チゴガニに寄生するMicrophalloides japonicusの被嚢幼虫(吸虫網:Microphallidae)」(共著)

木船悌嗣, 古賀庸憲

「長崎県生物学会誌」 ( 長崎県生物学会 ) 50 ( 50 ) 5 - 8 1999

Reproductive success and two modes of mating in the sand-bubbler crab Scopimera globosa

T Koga

JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY ( ELSEVIER SCIENCE BV ) 229 ( 2 ) 197 - 207 1998.11

Reproductive success of male (number of eggs fertilized by sperm of the male) and female (number of eggs extruded by the female) sand-bubbler crab, Scopimera globosa, was investigated in a field enclosure. The number of eggs extruded by females was positively correlated with their body size. Small males significantly tended to mate on the surface (surface mating, SM), while large males did so inside male burrows (underground mating, UM). The success ratio (matings per courtship) of UM (32%) was significantly lower than that for SM (69%). However, UM was more likely to be followed by oviposition (61%) than was SM (17%). These findings concur with previous studies suggesting that most females performing UM were ready for ovulation but those performing SM were not. During the study, 79% of eggs were fertilized by UM males, 10% by SM males and 11% were extruded without the female mating (presumably using stored sperm). Both burrowless and burrow-holding females engaged in SM, but only burrowless females engaged in UM. Discrete response of females to male mating attempts depending on females' occupancy of burrows is therefore an important factor in the maintenance of alternative mating tactics in male S. globosa. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

DOI

Elevated predation risk changes mating behaviour and courtship in a fiddler crab

T Koga, PRY Backwell, MD Jennions, JH Christy

PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES ( ROYAL SOC ) 265 ( 1404 ) 1385 - 1390 1998.08

The fiddler crab, Uca beebei, lives in individually defended burrows, in mixed-sex colonies on intertidal mud flats. Avian predation is common, especially of crabs unable to escape into burrows. Mating pairs form in two ways. Females either mate on the surface at their burrow entrance ('surface mating') or leave their own burrow and sequentially enter and leave ('sample') courting males' burrows, before staying in one to mate underground ('burrow mating'). We tested whether perceived predation risk affects the relative frequency of these mating modes. We first observed mating under natural levels of predation during one biweekly, semi-lunar cycle. We then experimentally increased the perceived predation risk by attracting grackles (Quiscalus mexicanus) to each half of the study site in two successive biweekly cycles. In each experimental cycle, crabs were significantly less likely to mate on the side with more birds. Moreover, on the side with elevated predation risk, the number of females leaving burrows to sample was greatly reduced relative to the number of females that surface-mated. Males waved less and built fewer mud pillars, which attract females, when birds were present. We discuss several plausible proximate explanations for these results and the effect of changes in predation regime on sexual selection.

Size-dependent mating behaviours of male sand-bubbler crab, Scopimera globosa: Alternative tactics in the life history

T Koga, M Murai

ETHOLOGY ( BLACKWELL WISSENSCHAFTS-VERLAG GMBH ) 103 ( 7 ) 578 - 587 1997.07

Factors leading to the separation of mating behaviours were investigated in the sand-bubbler crab, Scopimera globosa. The crabs mated on the surface (surface copulation, SC) and underground (UC). UC males mere large (old) whilst SC males were small (young). Burrowless females bred in the UC males' burrows. These females accepted UC in exchange for access to a burrow. UC occurred much more frequently than SC in the burrow area in which females oviposited. Most SC occurred in the water-saturated area affording a rich diet. SC was accepted by most large and small females in both areas and most UC by small females in the burrow area. SC was an alternative to UC for males in that there was a size dependence between types of copulation. These two mating behaviours involved different degrees of interaction with neighbouring males. Males attempting to carry a female to their burrows for UC were more often disturbed by other males than were males attempting SC. In the interaction for both UC and SC, larger males were likely to resist the disturbances. UC males needed their own burrows, bur these burrows were not enlarged before mating. UC males have a higher paternity of eggs than SC males, because SC males' sperm is often displaced by other males. Thus, UC was a behaviour with relatively higher costs and benefits for male crabs than SC behaviour, Alternative mating behaviours in male S. globosa are conditional, and explained by intrasexual interactions and a male life history strategy with a trade-off between growth and reproduction. It is nor likely that the size dependence of male mating behaviour is caused by mate preference of females for UC males in the burrow area.

Mate acceptance and guarding by male fiddler crabs Uca tetragonon (Herbst)

S Goshima, T Koga, M Murai

JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY ( ELSEVIER SCIENCE BV ) 196 ( 1-2 ) 131 - 143 1996.03

The fiddler crab, Uca tetragonon (Herbst) mates both on the surface near female-defended burrows and underground in male-defended burrows. In underground mating, which requires relatively high male investment, males attract both non-ovigerous and ovigerous females into their burrows by claw waving. Males aggressively expel some females soon after they enter their burrows and others after pair formation, but before females spawn. Finally males guard some females in their burrows until they spawn, which presumably ensures paternity. Males do not select mates of a particular body size, but they do differentially accept females with late-stage eggs, those about to release larvae and spawn another clutch. Except at the beginning of the reproductive season, few ripe non-ovigerous females are available because females spawn successively and only in moderate synchrony. By differentially accepting late stage ovigerous females, males may increase their fertilization rates because they minimize the time they spend guarding each of their mates to ensure their paternity. A male-biased operational sex ratio and a high last male advantage in sperm competition are two conditions that may have favored male choice based on female guarding time in this species.

DOI

Metacercaria of Gynaecotyla squatarolae (Digenea : Microphallidae) found in Scopimera globosa (Decapoda : Ocypodidae) on the seashore of the eastern part of Fukuoka City, Kyushu(共著)

KIFUNE T

Transactions of the Nagasaki Biological Society 47 51 - 54 1996

「福岡市東部沿岸産コメツキガニに寄生する微小二生吸虫Gynaecotyla squataroaeの被嚢幼虫」(共著)

木船悌嗣

「長崎県生物学会誌」 47 51 - 54 1996

Predation and cannibalism by the male fiddler crab Uca tetragonon

T Koga, S Goshima, M Murai, S Poovachiranon

JOURNAL OF ETHOLOGY ( SPRINGER JAPAN KK ) 13 ( 2 ) 181 - 183 1995.12

COURTSHIP AND THE EVOLUTION OF UNDERGROUND MATING IN UCA TETRAGONON (DECAPODA, OCYPODIDAE)

M MURAI, T KOGA, S GOSHIMA, S POOVACHIRANON

JOURNAL OF CRUSTACEAN BIOLOGY ( CRUSTACEAN SOC ) 15 ( 4 ) 655 - 658 1995.11

Uca tetragonon is an Indo-West Pacific species of fiddler crab in the narrow-front (NF) species group. Male Uca tetragonon used display by claw-waving to attract females into burrows of males for mating. Pairing attempts by male Uca tetragonon attracting conspecific females into their burrows occurred in 2 different ways. In type 1, males entered their burrows after their mates did, and, in type 2, males entered their burrows first and their mates followed. Both types occurred with similar frequencies. Rate of pair formation and spawning rate of paired females were not significantly different between the 2 types. Nine of 20 females spawned in the pooled data from both types.
In Indo-West Pacific fiddlers, type 1 pair formation (female first) has been found in the 5 subgenera (NF and the broad-front species (BF) group) and type 2 (male first) previously only in the BF group, but now also in Uca tetragonon. Type 1 is common to all subgenera of Uca in the Indo-West Pacific, a criterion typical of ancestral characters. Since NF and BF groups are distinctly different in phylogenesis as well as in their ecology, type 2 pair formation is supposed to be a derived behavioral character in NF fiddlers, having evolved independently from the BF group.

MOVEMENTS BETWEEN MICROHABITATS DEPENDING ON REPRODUCTION AND LIFE-HISTORY IN THE SAND-BUBBLER CRAB SCOPIMERA-GLOBOSA

T KOGA

MARINE ECOLOGY PROGRESS SERIES ( INTER-RESEARCH ) 117 ( 1-3 ) 65 - 74 1995.02

Sand-bubbler crabs Scopimera globosa inhabit burrows in the upper tidal sand flat and form droves in the water-saturated area of the lower tidal flat. To elucidate the function of the movements between the microhabitats in this species, I investigated the change in population density, crab body size and reproductive conditions of both sexes within each microhabitat. Ovigerous females were found in the burrow area while spent females (releasing zoea recently) were concentrated in the water-saturated area. Gonad weights of nonovigerous females in the burrow area were higher than those in the water-saturated area. Both male and female crabs in the water-saturated area, where diet quality (organic nitrogen content of the surface substratum) exceeded that in the burrow area, spent more time foraging and suffered less from interactions with neighbours than crabs in the burrow area. In contrast, although both gonad and hepatopancreas weights of males decreased with time in the early to mid reproductive season, there was no difference in male body condition between microhabitats. Few crabs moved between the microhabitats in the mid to late reproductive season, indicating that most crabs active in the water-saturated area during low tides did not return to the burrow area during high tides, differing from the movements of other ocypodid species. S. globosa have alternative mating behaviours, underground copulation (UC) and surface copulation (SC). UC, followed by oviposition, was dominant in the burrow area, though both UC and SC were conducted there. In contrast, SC, not always followed by oviposition, was dominant in the water-saturated area. Females maximized their use of the microhabitats, i.e. the burrow area for mating, oviposition and incubation and the water-saturated area for foraging and partly for mating. The operational sex ratio was biased towards males in the burrow area and towards females in the water-saturated area, due to the fact that the last male to mate fertilizes most of the eggs extruded by a female. A high proportion of large (i.e. older) crabs of both sexes stayed in the burrow area during the reproductive season, whereas small (young) crabs spent most of their time in the water-saturated area for growth. Thus, the crabs made suitable use of their time in different microhabitats under a Life history strategy.

SEXUAL DIFFERENCES IN FORAGING BEHAVIOR OF SIKA-DEER, CERVUS-NIPPON

T KOGA, Y ONO

JOURNAL OF MAMMALOGY ( AMER SOC MAMMALOGISTS ) 75 ( 1 ) 129 - 135 1994.02

We compared the foraging behavior of five age-sex classes of sika deer (Cervus nippon nippon) in grasslands in Nozaki Island, Japan. Seasonal changes in feeding time and food plants were greater for males than for females. For males, feeding time decreased and time allocated to social activities increased with age in the breeding season. In spring, when antlers of deer began to regrow, adult males spent more time feeding on plants with high ash contents than did younger males and females. In winter, males spent more time feeding on plants with high protein content than did females. The trend was much different from that reported in many previous investigations, perhaps because of abundant food in our study area, which was at a low latitude.

MATING-BEHAVIOR OF THE SAND BUBBLER CRAB SCOPIMERA-GLOBOSA

Y HENMI, T KOGA, M MURAI

JOURNAL OF CRUSTACEAN BIOLOGY ( CRUSTACEAN SOC ) 13 ( 4 ) 736 - 744 1993.11

The mating behavior of the sand bubbler crab Scopimera globosa was studied in an intertidal area of Fukuoka, Japan, from 1988-1991. This species mates both on the surface and underground, as do some fiddler crabs. In surface copulations, wandering males mate sequentially with resident females beside burrows of females. In underground copulations, resident males chase and capture wandering females, carry them to their burrows and push them below. Males then enter their burrows and plug them within minutes. Pairs presumably copulate in these burrows. Unlike the fiddler crabs, however, most females that stayed in burrows of males did not have mature ovaries and wandered again within a few days. Consequently, only 30% of the females that stayed in burrows of males spawned in those burrows. After the spawning, males abandoned their burrows, while females remained in them during incubation. Thus, forced copulation characterizes the mating system of this species, though there is room for female choice. Mating success was much lower in underground than in surface copulation. However, males that succeed in forcing females into their burrows may gain a reproductive advantage, because the sperm of the last male to mate with a female prior to egg extrusion is used to fertilize most of the eggs.

SPERM COMPETITION AND THE ASSURANCE OF UNDERGROUND COPULATION IN THE SAND-BUBBLER CRAB SCOPIMERA-GLOBOSA (BRACHYURA, OCYPODIDAE)

T KOGA, Y HENMI, M MURAI

JOURNAL OF CRUSTACEAN BIOLOGY ( CRUSTACEAN SOC ) 13 ( 1 ) 134 - 137 1993.02

Studies of sperm competition are necessary for understanding mating systems in species where two or more males copulate with a single female. We studied fertilization ratios of successive male mates in the sand-bubbler crab Scopimera globosa (de Haan) (family Ocypodidae). Males copulate on the surface or pair underground. The male pairing underground is the last to inseminate the female before she extrudes eggs, as is the case in most ocypodid crabs. In serial mating experiments using irradiated and normal males, the last male to mate fertilized over 90% of the eggs. Females forced to mate in the burrows of irradiated males extruded infertile eggs, indicating that sperm transfer occurred in the burrow.

TERRITORIAL BEHAVIOR OF BOTH SEXES IN THE WATER STRIDER METROCORIS-HISTRIO (HEMIPTERA, GERRIDAE) DURING THE MATING SEASON

T KOGA, K HAYASHI

JOURNAL OF INSECT BEHAVIOR ( PLENUM PUBL CORP ) 6 ( 1 ) 65 - 77 1993.01

Territorial behavior of overwintered individuals of Metrocoris histrio was observed in an upstream area. Adults of both sexes held territories, but male territories were larger than those of females. Severe competition occurred among males for territories which give them access to receptive females. The effects of male body length and midleg length on establishment of territories were not significant. The effect of female midleg length on activity of females entering preferred foraging sites was equally not significant. Instead, territorial behavior increased with male age and males stayed longer at prime sites. Females of intermediate age were likely to occupy prime sites. Females had longer territory residence time than males. The sexes were dimorphic with respect to midleg length, and dimorphism in M. histrio may be related to a difference in life history, in that sexual selection may be relaxed due to asynchronous adult emergence patterns.

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