Pairs during hibernation in a temperate frog: an unusual male mating strategy among anurans

Abstract

Amplexus in which a male grasps a female from behind, characterizes most anurans as their strategy to ensure mating success. The behavior usually takes place some minutes, hours or days before gamete release. In a few species, however, it forms very early and lasts up to months, assumed to be an extreme pattern of mate guarding. Rana chensinensis is a temperate frog endemic to northern China. They hibernate in water in groups and breed explosively. At 15 sites across the species’ range, we found that on average 34% (17–67%) of hibernating adult females were paired, and these pairs were initiated shortly before hibernation and remained until spawning, lasting up to 5 months for the northern populations. Data from a focal study site showed that paired males and females were both larger in body size than their non-paired counterparts, and that there was a positive relationship between the body sizes of the paired frogs. The proportion of females that were paired was positively related with hibernating group size and independent of the sex ratio of the adults in a refuge. We interpret the extended pairing behavior as a male strategy that facilitates the avoidance of intense intra-sexual competition in mating aggregations during the breeding period and the starting of spawning earlier to acquire additional females.