Hybrid female matings are directly related to the availability of Rana lessonae and Rana esculenta males in experimental populations

In the hybridogenetic frog complex Rana lessonae and Rana esculenta, mate choice based on genetic benefit could be an important form of sexual selection. The hybrid R. esculenta, must coexist with the parental species R. lessonae, which functions as a genetic host, The two types occur in varying ratios in natural populations depending on environmental conditions of the aquatic habitat. In highly disturbed habitats such as gravel pits, R. esculenta is most common, whereas R. lessonae is more frequent under less disturbed environmental conditions. To examine the influence of different proportions of males of the two types on mating success, we subjected hybrid females to different ratios of R. lessonae and R. esculenta males in artificial pools. Our results show that females mated according to the availability of the two types of males in the pools. However, combining data over all ratio treatments suggested a slightly higher mating frequency for R. lessonae males than for R. esculenta males, although the R. esculenta males behaved more aggressively called more often, and tended to orient more frequently toward females than did R. lessonae males. This, plus results from previous mate choice studies, suggests that R. esculenta females have a preference for mating with R. lessonae males because of genetic benefits; but which mate a female finally mates with is also influenced by other processes, such as the availability of the two male types at the time of mate choice as well as the strength of male-male competition.