Conspecific and Heterospecific Pair-formation in Rana porosa brevipoda and Rana nigromaculata, with Reference to Asymmetric Hybridization

Abstract

Patterns of conspecific and heterospecific pair-formation in Rana porosa brevipoda and Rana nigromaculata were investigated in the field. In R. porosa brevipoda, most of the conspecific pairs were formed by female initiation. Size-assortative mating was observed in R. porosa brevipoda. On the other hand, most of the conspecific pairs of R. nigromaculata were formed by forced clasping by males. There was no significant correlation between the male and female sizes in amplectant pairs of R. nigromaculata. Of a total of 12 heterospecific pairs observed, 11 were pairs between male R. nigromaculata and female R. porosa brevipoda. The proximate factors of the asymmetry in heterospecific pairing are discussed with relation to the differences in the pairing patterns, body size, and the body shape between the two species. Possible impacts of the asymmetric hybridization on the two species are also discussed.