Faculty Profiles - KOGA Tsunenori

Published Papers - KOGA Tsunenori

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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.

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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.

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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.

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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.

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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.

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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.

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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]

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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.

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

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

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.

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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.

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Published Papers - KOGA Tsunenori