研究者データベース

石原 千晶(イシハラ チアキ)
水産科学研究院 海洋生物資源科学部門 海洋生物学分野
助教

基本情報

通称等の別名

    安田 千晶

所属

  • 水産科学研究院 海洋生物資源科学部門 海洋生物学分野

職名

  • 助教

学位

  • 博士(水産科学)(北海道大学)

J-Global ID

研究活動情報

論文

  • Chiaki I. Yasuda, Masaya Otoda, Reiko Nakano, Yuki Takiya, Tsunenori Koga
    ECOLOGICAL RESEARCH 32 3 347 - 357 2017年05月 [査読有り][通常論文]
     
    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.
  • Chiaki I. Yasuda, Tsunenori Koga
    BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY 70 12 2175 - 2183 2016年12月 [査読有り][通常論文]
     
    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.
  • Chiaki I. Yasuda, Tsunenori Koga
    JOURNAL OF ETHOLOGY 34 3 249 - 254 2016年09月 [査読有り][通常論文]
     
    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.
  • Matsuo Kento, Tanikawa Daisuke, Yasuda Chiaki I, Wada Satoshi
    MARINE ECOLOGY-AN EVOLUTIONARY PERSPECTIVE 36 4 1391 - 1399 2015年12月 [査読有り][通常論文]
  • Hasaba Yukari, Yasuda Chiaki I, Wada Satoshi
    ANIMAL BEHAVIOUR 107 1 - 5 2015年09月 [査読有り][通常論文]
  • Yasuda Chiaki I, Matsuo Kento, Wada Satoshi
    BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY 69 8 1287 - 1292 2015年08月 [査読有り][通常論文]
  • Chiaki I. Yasuda, Kento Matsuo, Yukari Hasaba, Satoshi Wada
    ANIMAL BEHAVIOUR 96 49 - 57 2014年10月 [査読有り][通常論文]
     
    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.
  • Yutaro Suzuki, Chiaki Yasuda, Fumio Takeshita, Satoshi Wada
    MARINE BIOLOGY 159 9 1991 - 1996 2012年09月 [査読有り][通常論文]
     
    Male mate choice has recently been reported in some animals with male-male competition. In the laboratory, we examined whether males choose their mates based on female quality that was indicated by body size and/or days to prenuptial molt, and the effects of female quality on male-male competition in the hermit crab Pagurus nigrofascia. We collected samples from April to May 2009 at an intertidal shore in Hokkaido, Japan (41A degrees N, 140A degrees E). When a male simultaneously encountered two receptive females in the mate choice experiment, males chose females which require less time to molt. When a male guarding a female with less time to molt was challenged by an intruder, the guarding male defended the female for a longer period and was more likely to win the contest. These results indicate that male P. nigrofascia use time to molt to discriminate between females.
  • Chiaki Yasuda, Fumio Takeshita, Satoshi Wada
    ANIMAL BEHAVIOUR 84 2 385 - 390 2012年08月 [査読有り][通常論文]
     
    Assessment of their own resource-holding potential (RHP) and that of their opponent affects the behaviours individuals use in contest competition. Contestants may use their own RHP and/or the relative RHP of opponents to make decisions and may switch these two assessment tactics during fighting. In male-male contests of hermit crabs Pagurus middendorffii, we examined whether contestants switch assessment tactics and whether they assess body size or major cheliped size as an index of RHP. Males of this species show precopulatory guarding behaviour, and male-male contests often occur when males guarding females encounter intruder males. We conducted trials of dyadic contests to investigate the assessment tactics in two phases of the contest: initial and combat. Intruders gave up the contest without escalating to physical combat when they were smaller. When physical combat occurred, it lasted longer if the difference in size of the major cheliped between guarding males and intruders was small, and males with a larger major cheliped than the opponent had a higher probability of winning the contests. These results suggest that P. middendorffii uses its own body size during the initial phase of a contest and relative major cheliped size during the combat phase to assess RHP. (C) 2012 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
  • Chiaki Yasuda, Yutaro Suzuki, Satoshi Wada
    MARINE BIOLOGY 158 10 2327 - 2334 2011年10月 [査読有り][通常論文]
     
    Functions of the major cheliped in pagurid hermit crabs have been studied in fights for shells. The major cheliped often shows sexual size dimorphism, suggesting that sexual selection favors the development of the male major cheliped. The function of the major cheliped in male-male competition was examined in Pagurus nigrofascia collected from April to June 2009 on the intertidal rocky shore in southern Hokkaido, Japan (41 degrees N, 140 degrees E). Sexual size dimorphism of the major cheliped was observed, and precopulatory guarding males had larger major chelipeds than solitary ones. Guarding males used the major cheliped to deter intruders during competitive interactions. Males without a major cheliped were disadvantaged even if they were larger than opponents and had ownership. Cheliped size affected the outcomes of contests between similar sized males. This suggests that the male major cheliped in P. nigrofascia protects mates from competitors and, consequently, enhances male mating success. Sexual selection may favor the development of the major cheliped in male pagurids.

その他活動・業績

  • 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年02月15日 [査読無し][通常論文]
  • 石原(安田) 千晶 日本水産学会誌 84 (4) 764 -764 2018年 [査読無し][通常論文]
  • 石原(安田) 千晶, 和田 哲 CANCER 27 (0) 1 -5 2018年 [査読無し][通常論文]
  • 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年08月 [査読無し][通常論文]
  • 加我 夏美, 石原(安田) 千晶, 和田 哲 Cancer (25) 9 -16 2016年08月 [査読無し][通常論文]
  • 小島 早智, 石原(安田) 千晶, 和田 哲 Cancer (25) 17 -24 2016年08月 [査読無し][通常論文]
  • 為近 昌美, 石原(安田) 千晶, 和田 哲 Cancer (25) 25 -27 2016年08月 [査読無し][通常論文]
  • 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年06月30日 [査読無し][通常論文]
  • 小島 早智, 石原(安田) 千晶, 和田 哲 CANCER 25 (0) 17 -24 2016年 [査読無し][通常論文]
     
    <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>
  • 為近 昌美, 石原(安田) 千晶, 和田 哲 CANCER 25 (0) 25 -27 2016年 [査読無し][通常論文]
  • 加我 夏美, 石原(安田) 千晶, 和田 哲 CANCER 25 (0) 9 -16 2016年 [査読無し][通常論文]
     
    <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>
  • 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年 [査読無し][通常論文]
     
    <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>
  • 松尾 謙人, 石原(安田) 千晶, 和田 哲 CANCER 24 (0) 21 -23 2015年 [査読無し][通常論文]
  • 福沢 仁之, 石原 千晶 堆積学研究会報 37 (37) 21 -30 1992年 [査読無し][通常論文]
     
    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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