Researcher Database

Chiaki Ishihara Yasuda
Faculty of Fisheries Sciences Marine Bioresource and Environmental Science Marine Biology and Biodiversity
Assistant Professor

Researcher Profile and Settings


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

Job Title

  • Assistant Professor

J-Global ID

Research Activities

Published Papers

  • Chiaki I. Yasuda, Masaya Otoda, Reiko Nakano, Yuki Takiya, Tsunenori Koga
    ECOLOGICAL RESEARCH 32 (3) 347 - 357 0912-3814 2017/05 [Refereed][Not invited]
    Sexual size dimorphism is a common phenomenon in the animal kingdom, and its seasonal change has been reported in some species that possess traits dimorphic only in males and specialized for male mating success. However, few studies have examined seasonal change in sexual dimorphism of traits possessed by both sexes. Here, we examined the reproductive biology of the hermit crab Pagurus minutus, at a sandflat in the Waka River estuary, Japan, with special reference to seasonal changes in sexual dimorphism of the large claw (major cheliped) size by conducting population and precopulatory guarding-pair sampling. Previous investigation demonstrated that the major cheliped is used as a weapon, and its size, more than body size, determines the winner in male-male contests of this species. We found ovigerous females from November to April, peaking in January, when 80% of females were ovigerous. Sexual size dimorphism of the major cheliped was observed; the degree of dimorphism increased in the reproductive season, when only males possessed an enlarged major cheliped. In addition, in the reproductive season, precopulatory guarding males had a larger body and larger relative size of the major cheliped than did solitary males, although the major cheliped size in guarding males seemed to reach an upper limit. These results suggest that seasonal change in sexual dimorphism of the major cheliped size in P. minutus strongly reflects sexual selection favoring the development of this natural weaponry, and that the degree of the dimorphism might be limited through natural selection.
  • Yasuda Chiaki I, Koga Tsunenori
    BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY 70 (12) 2175 - 2183 0340-5443 2016/12 [Refereed][Not invited]
  • Yasuda Chiaki I, Koga Tsunenori
    JOURNAL OF ETHOLOGY 34 (3) 249 - 254 0289-0771 2016/09 [Refereed][Not invited]
  • Matsuo Kento, Tanikawa Daisuke, Yasuda Chiaki I, Wada Satoshi
    MARINE ECOLOGY-AN EVOLUTIONARY PERSPECTIVE 36 (4) 1391 - 1399 0173-9565 2015/12 [Refereed][Not invited]
  • Hasaba Yukari, Yasuda Chiaki I, Wada Satoshi
    ANIMAL BEHAVIOUR 107 1 - 5 0003-3472 2015/09 [Refereed][Not invited]
  • Yasuda Chiaki I, Matsuo Kento, Wada Satoshi
    BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY 69 (8) 1287 - 1292 0340-5443 2015/08 [Refereed][Not invited]
  • Chiaki I. Yasuda, Kento Matsuo, Yukari Hasaba, Satoshi Wada
    ANIMAL BEHAVIOUR 96 49 - 57 0003-3472 2014/10 [Refereed][Not invited]
    Prior contest outcomes often affect subsequent contest behaviour (winner/loser effects). If contestants discriminate between familiar and unfamiliar opponents, individual recognition may alter the strength and/or manner of winner/loser effects. We examined whether hermit crabs, Pagurus middendorffii, changed their contest behaviour based on winner/loser effects, whether they distinguished a familiar opponent from an unfamiliar opponent, and how the familiarity with the opponent related to the winner/loser effects in male-male contests. Males of this species show precopulatory guarding behaviour, and male-male contests often occur between a guarding male and an intruder. In contests between unfamiliar males, intruders use self-assessment during the initial contact phase and mutual assessment during the physical combat phase to determine their behaviours. Precopulatory guarding males and females collected in the field were used in two consecutive trials of male-male contests. Losers in the first trial were used as focal intruders in the second trial with (1) a familiar opponent that had won the first trial, (2) an unfamiliar opponent that had won the first trial with another intruder, or (3) a naive opponent with no trial experience. Focal intruders did not alter their aggressiveness against either unfamiliar or naive opponents in the second trial. However, they rarely initiated physical combat against familiar opponents in the second trial. When they initiated combat, they gave up sooner against familiar opponents than against unfamiliar opponents. These results suggest that intruders are able to distinguish familiar opponents from others and decrease their aggressiveness only when they encounter familiar opponents. Our study therefore shows loser effects in P. middendorffii related to the familiarity with the opponent and suggests intruders can obtain information about their opponents during the initial encounter. (C) 2014 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
  • Suzuki Yutaro, Yasuda Chiaki, Takeshita Fumio, Wada Satoshi
    MARINE BIOLOGY 159 (9) 1991 - 1996 0025-3162 2012/09 [Refereed][Not invited]
  • Yasuda Chiaki, Takeshita Fumio, Wada Satoshi
    ANIMAL BEHAVIOUR 84 (2) 385 - 390 0003-3472 2012/08 [Refereed][Not invited]
  • Yasuda Chiaki, Suzuki Yutaro, Wada Satoshi
    MARINE BIOLOGY 158 (10) 2327 - 2334 0025-3162 2011/10 [Refereed][Not invited]


  • 和田哲, 守田安祐美, 石原(安田)千晶  海洋と生物  40-  (1)  106‐113  -113  2018/02  [Not refereed][Not invited]
  • 石原(安田) 千晶  日本水産学会誌  84-  (4)  764  -764  2018  [Not refereed][Not invited]
  • I. Yasuda Chiaki, Wada Satoshi  CANCER  27-  (0)  1  -5  2018  [Not refereed][Not invited]
  • 中野 玲子, 石原(安田) 千晶, 古賀 庸憲  日本ベントス学会誌  71-  (1)  32  -36  2016/08  [Not refereed][Not invited]
  • 加我 夏美, 石原(安田) 千晶, 和田 哲  Cancer  (25)  9  -16  2016/08  [Not refereed][Not invited]
  • 小島 早智, 石原(安田) 千晶, 和田 哲  Cancer  (25)  17  -24  2016/08  [Not refereed][Not invited]
  • 為近 昌美, 石原(安田) 千晶, 和田 哲  Cancer  (25)  25  -27  2016/08  [Not refereed][Not invited]
  • 塩崎祐斗, 寺島杏奈, 石原(安田)千晶, 古賀庸憲  南紀生物  58-  (1)  48‐51  2016/06  [Not refereed][Not invited]
  • Kojima Sachi, Yasuda Chiaki I, Wada Satoshi  CANCER  25-  (0)  17  -24  2016  [Not refereed][Not invited]
    <p>In species with both male–male contests and male mate choice, dominance hierarchy in males may affect the male mate choice. This study described patterns of precopulatory guarding pairs of the hermit crab <i>Pagurus nigrofascia</i> in the field to infer variation in male mate choice based on male body size. We found size assortative pairing in precopulatory guarding pairs collected in the field, and that larger males tended to guard females with a shorter time until molting in the field. To examine whether prior outcomes of male–male contests affect male mate choice in <i>P. nigrofascia</i>, we conducted an experiment where a male with a winning or losing experience in male–male contests was placed in a container with two receptive females, and recorded the outcomes of male mate choice. An interaction between two variables of male experiences and time until female molting was statistically significant, indicating that males with a winning experience were likely to choose females with a shorter time until molting while males with losing experience were likely to choose females with longer time until molting. Small inferior males might guard females with low quality as a prudent mate choice in the field.</p>
  • Tamechika Masami, Yasuda Chiaki I, Wada Satoshi  CANCER  25-  (0)  25  -27  2016  [Not refereed][Not invited]
  • Kaga Natsumi, Yasuda Chiaki I, Wada Satoshi  CANCER  25-  (0)  9  -16  2016  [Not refereed][Not invited]
    <p>To examine whether solitary males that had been single in the field are less active in male–male contests than those had been paired in the field in the hermit crab <i>P. filholi</i>, we conducted a laboratory experiment of male–male contests to compare the behaviors of challenger males that had been found not paired in the field (N-male), or had guarded other females in the field (G-male). We introduced a challenger male and a guarding pair into an experimental container and observed the behaviors of challenger males. N-males showed a significantly lower frequency of initiating contests than G-males. Time to initiate contests in N-males was longer than that in G-male. Difference in body size between male contestants significantly affected the time to initiate contests, contest duration and contest outcome, but female quality did not affect these variables. We suggest that solitary males of <i>P. filholi</i> in the field would not be always active for competition for mates, which will decrease intensity of sexual selection in this species.</p>
  • NAKANO Reiko, YASUDA Chiaki I, KOGA Tsunenori  Japanese Journal of Benthology  71-  (1)  32  -36  2016  [Not refereed][Not invited]
    <p>The pattern of egg production is important for understanding the reproductive biology in various animals. In species that can spawn multiple clutches during a single reproductive season, egg number and/or size in a population often show temporal changes even within a single season. However, there are only a few studies examining the temporal patterns of egg production in decapod crustaceans including hermit crabs. In this study, we investigated whether the clutch size and egg size change during a single breeding season in the hermit crab <i>Pagurus minutus</i>. We collected precopulatory guarding pairs from December 2014 to April 2015 and recorded the clutch and egg size of the newly spawned eggs. Our results demonstrated that both the clutch size and the egg size varied over this period; fewer and larger-sized eggs were laid in December, whereas eggs laid in February were greater in numbers and smaller in size. Given the temporal changes in environmental conditions in the study area, larvae from the two types of eggs experience different conditions. Former larvae are expected to hatch in February and experience a lower water temperature with relatively poor food conditions, whereas the latter are expected to hatch in April, when the feeding conditions are considered better with relatively warmer water temperatures. The pattern of egg production in this species is thought to vary with the environmental conditions at the time of larval hatching.</p>
  • Matsuo Kento, Yasuda Chiaki I, Wada Satoshi  CANCER  24-  (0)  21  -23  2015  [Not refereed][Not invited]
  • FUKUSAWA Hitoshi, ISHIHARA Chiaki  Journal of the Sedimentological Society of Japan  37-  (37)  21  -30  1992  [Not refereed][Not invited]
    Our purpose is to clarify Late Oligocene to Early Miocene paleoceanographic changes in the back-arc region of the Kuril Arc. We have only a few of reports on sedimentological and organic geochemical considerations as the Paleogene formations around the Sea of Okhotsk, which prompted us to research.<br>Kitami area, our research field, is located on the back-arc region of the Kuril Arc (Fig. 1), and has Tatsukobu-Tsubetsu biosiliceous deposit whose thickness attains more than 2500m. Based on biostratigraphic and rediometric ages, Tatsukobu-Tsubetsu biosiliceous deposit appears to be accumulated during the period ranging from Late Oligocene to earliest Early Miocene. This biosiliceous deposit begins with a basal sandstone including glauconite, which rests unconformably upon the Wakamatsuzawa Formation including silicified woods and roots. According to lithostratigraphic correlations, andesitic volcaniclastic bed of the upper part and acidic tuff bed of the middle part of the Tatsukobu Formation in the Kitami area are correlated to biotite-rich acidic tuff bed and hornblende-rich welded tuff bed in the Ponki-Ashoro area. Radiometric ages of acidic tuff bed and welded tuff bed in the Ponki-Ashoro area indicate 23.8Ma (fission track age) and 27.4Ma (K-Ar age).<br>To clarify the marine primary production of Tatsukobu-Tsubetsu biosiliceous deposit, we measured organic carbon congtents, C-H-N-O compositions of kerogen (insoluble organic matter) and Sulphur contents. Atomic composition analysis of kerogen concentrates is to examine the presence of terrigenous organic carbon. Plotted in a &ldquo;van Krevelen Diagram&rdquo; (i.e., H/C vs. O/O), estimated marine organic carbon (EMOC) and estimated non -marine organic carbon (ENOC) were calculated.<br>Based on stratigraphic changes in the amount of EMOC and ENOC, Tatsukobu biosiliceous deposit was divided into three stages.<br>In Depth 1335m-1450m and Depth 0m-350m (Fig. 5), stratigraphic variations in the amount of EMOC are parallel to those of ENOC. However, increase in EMOC are associated blosely with decrease in ENOC within Depth 350m-1335m. EMOC/ENOC ratios indicate that organic matter within Depth 350m-1335m included higher contents of marine-origin organic materials than those within other horizon. According to sedimentary petrological investigations, this deposit also contains larger volume of non-siliceous rocks in Depth 350m-1335m than in other horizon. In the past ocean, we conclude that amount of nutrients and dissolved silica components derived from land were parallel to those of ENOC. If this had happened at the back-arc region of the Kuril Arc during Late Oligocene to earliest Early Miocene, nutrients of deep water-origin contributed more to marine primary production than those of land-origin at the time of Depth 350m-1335m. This presumption suggests that the proto form of the Kuril Basin served as a vessel of nutrient-rich and silica-poor deep water at about 27.4Ma (Fig. 2).

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