Hamasaki Katsuyuki, Dan Shigeki
Department of Marine Biosciences, Tokyo University of Marine Science and Technology, Konan, Minato, Tokyo 108-8477, Japan. E-mail:
Zool Stud. 2021 Apr 18;60:e18. doi: 10.6620/ZS.2021.60-18. eCollection 2021.
Decapod crustaceans develop secondary sexual structures, such as large chelipeds for weaponry and/or display in males and a wider pleon for incubating eggs in females. These structures should be costly to produce and maintain; hence, the crustacean reproductive strategy might have adapted to conserve energy for developing secondary sexual characteristics during the reproductive season. However, little is known about seasonal changes in the sexual size dimorphisms of the chelipeds and pleons of decapod crustaceans. Anomuran crabs from the family Porcellanidae exhibit a true crab-like body shape, with relatively large chelipeds for their body size and a well-developed pleon. They also show sexual size dimorphism (, males with larger chelipeds and females with wider pleons); therefore, it was expected that seasonal changes in the sexual size dimorphisms of these organs would occur in porcellanid crabs. We tested this expectation using , which is common on the intertidal cobble and boulder shores of the temperate and tropical regions of Japan. We employed allometric growth analyses of the cheliped and pleon dimensions of females and males collected over a year. Our analyses supported our expectation regarding the seasonal changes in the sexual size dimorphisms of the chelipeds and pleons in . Intersexual size dimorphism of the chelipeds and pleons was evident during the breeding season: females allocated more energy to pleon growth, while reducing cheliped growth, and investment in the pleon increased with increasing female body size, whereas males invested their energy in cheliped growth, and the investment in chelipeds increased with increasing male body size. During the nonbreeding season, females and males conserved energy by reducing the size of pleons and chelipeds relative to their respective body sizes. Our results highlighted the sex-specific and season-dependent resource allocation and reproductive strategies of porcellanid crabs.
十足目甲壳动物会发育出第二性征结构，比如雄性用于争斗和/或展示的大型螯足，以及雌性用于抱卵的更宽的腹部。这些结构的产生和维持成本应该很高；因此，甲壳动物的繁殖策略可能已经适应于在繁殖季节节省能量以发育第二性征。然而，对于十足目甲壳动物螯足和腹部的两性异形的季节性变化知之甚少。瓷蟹科的异尾类蟹呈现出真正的蟹状体型，相对于它们的体型而言，螯足相对较大，腹部发育良好。它们也表现出两性异形（雄性螯足更大，雌性腹部更宽）；因此，预计这些器官的两性异形在瓷蟹中会出现季节性变化。我们使用在日本温带和热带地区潮间带的鹅卵石和巨石海岸很常见的[某种瓷蟹]来检验这一预期。我们对一年中收集的雌性和雄性[瓷蟹]的螯足和腹部尺寸进行了异速生长分析。我们的分析支持了我们对于[瓷蟹]螯足和腹部两性异形季节性变化的预期。在繁殖季节，螯足和腹部的两性间尺寸差异很明显：雌性将更多能量分配给腹部生长，同时减少螯足生长，并且随着雌性体型增大，对腹部的投入增加，而雄性则将能量投入到螯足生长中，并且随着雄性体型增大，对螯足的投入增加。在非繁殖季节，雌性和雄性通过相对于各自体型减小腹部和螯足的尺寸来节省能量。我们的结果突出了瓷蟹性别特异性和季节依赖性的资源分配及繁殖策略。
