Agonistic and mating behavior in relation to chela features in Hemigrapsus takanoi and H. sinensis (Brachyura, Varunidae)

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Relative growth of chelae and the area of setal patches was investigated for Hemigrapsus takanoi, in which only males have setal patches on chelae, and for H. sinensis, in which both sexes have setal patches. Chelae and setal patches increased with body size in both species. In H. takanoi, chela size and size increment relative to body size was larger in males than in females. In H. sinensis, chela size relative to body size was larger in males than in females, but size increment was not different between the sexes. Sexual dimorphism of chelae is more prominent in H. takanoi than in H. sinensis. Laboratory observations of intrasexual agonistic interactions revealed that the interaction occurred more frequently in H. takanoi than in H. sinensis without any sexual difference in either species. In agonistic interactions by H. takanoi, males mostly used chelae, while females employed their walking legs. By contrast, both sexes of H. sinensis used chelae more frequently than walking legs in agonistic interactions. In mating behavior, both species made a copulative posture without courtship behavior. Males of H. takanoi handled females with chelae during mating behavior, whereas in H. sinensis, chela handling was infrequent. All the findings suggest the extent of sexual dimorphism of chela is correlated with sexual difference of chela use in social behavior.
2012-12-00