STUDIES FOR THE PRESERVATION OF CLOSE-SPECIES RECHNESS

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The clarification of the mechanism for the close-species coexistence is useful for the preservation of species richness. The diversity of the behavior, especially mating behavior is considered to make the reproductive isolation among the close species and to promote the coexistence of them. I studied the diversity of the mating system of semi-terrestrial crabs, Ocypodidae and Mictyridae, which inhabit shores.The fiddler crabs (Ocypodidae ; genus Uca) more than 80 species are distributed the tropical and subtropical shores in the Old and New Worlds. In general, some species inhabit the same shore. The male fiddler crab waves its hypertroph, major cheliped, and courts to the female crabs. I examined the preference for the female's body color by the male crabs, based on the above mating behavior. It was clarified that the female's body color was selected by the male crabs. This result suggests that the variation of body color makes and keeps the reproductive isolation among the close species, and promotes the coexistence of them.The mating system of the soldier crab, Mictyris brevidactylus , differed from that of the fiddler crabs. The soldier crabs changed their activity pattern between reproductive and non reproductive seasons. In the reproductive season, the females fed on beneath the sand roof which was made by sand pellets. In contrast, the males appeared on the ground surface. After engaging in their surface activity, the male crabs entered the females tunnel and mated in the burrows. That is, the males searched their mates using the tunnel of the female as a guide post. These studies showed that the variation of the mating system is related to the diversity of crabs on the shore.