Opportunity for sexual selection arises at moderate densities in the frog Rana chensinensis: an experimental approach

Abstract

Heavily male-biased operational sex ratio and high male density characterizing explosively breeding anurans are expected to enhance the opportunity for sexual selection through large-male mating advantage brought about by severe male–male competition. However, our previous study on the temperate frog Rana chensinensis suggested that these two factors might restrict the opportunity under natural conditions for females to be grasped by any male they meet first, and scramble competition between males occurred less frequently because amplectant pairs hid on the bottom of ponds. In the present experimental study, in which the operational sex ratios and male densities were much lower and individual interactions were sufficiently longer than in natural population, we found a large-male pairing advantage in female mate choice, multiple mate choice, and male displacement experiments. These findings lend circumstantial support for the predication, although there was no evidence of large-female mating advantage in a male mate choice experiment.