Breeding behaviour and hybridization: variation in male chorusing behaviour promotes mating among taxa in waterfrogs

Identifying the proximate basis of heterospecific matings in hybrid populations could significantly advance our understanding of mate recognition. As females are often considered to be the more selective sex, most studies have focused only on female mate choice. However, male behaviour often plays a determinant role in sexual selection. In the European waterfrog hybridization complex, the unbalanced mating frequency observed between hybrid females Rana esculenta and the parental species Rana lessonae has been attributed to a preference of these females for heterospecific males. In this study, for the first time we investigated the behaviour of males from three taxa (two parental species and the hybrid) in natural choruses. It appears that the three waterfrog taxa differ in their mating behaviour. We found that the breeding behaviour of R. lessonae males (i.e. low-frequency territorial call, close intermale proximity, movement not limited to a small area) suggests that they do not defend any territory. This constitutes evidence that R. lessonae males compete to outrace rivals to receptive females. Apart from the acoustic behaviour that appears to be intermediate between that of the two parental species, the other behavioural traits of the hybrid resemble those of the parental species Rana ridibunda (aggressive and territorial behaviours). These results suggest a genetic basis to these complex behavioural traits. From an ecological point of view, we conclude that the strong under-representation of hybrid males observed in amplexus can be due to the maladaptive hybrid reproductive tactic in mixed choruses. (c) 2007 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.