Sexual selection in the lek-breeding European treefrog: body size, chorus attendance, random mating and good genes

Variation in male reproductive performance and success was studied over 2 years in a population of individually marked European treefrogs, Hyla arborea, a hylid frog with prolonged breeding season and a lek mating system. Reproductive success in males was not related to body size, age or growth rate, and there was no evidence for size- or age-assortative mating. Male mating success was significantly correlated with chorus attendance, that is, the number of nights spent calling at the breeding site. There were no significant differences with regard to body size, age or growth rate between males surviving to the next breeding season and those not surviving. However, surviving males showed a significantly higher chorus attendance than nonsurviving males, which is a novel finding for lekking anurans. Furthermore, males that survived from the previous breeding season spent significantly more nights calling at the breeding site than males that were observed for the first time. Since calling in frogs is costly, these results suggest that chorus attendance reflects male quality. The distribution of male mating success did not differ from a Poisson distribution, indicating a random mating pattern. Since male quality is related to chorus attendance, females that mate randomly are likely to mate with high-quality males and thereby gain indirect genetic benefits without incurring costs of extended mate searching and mate assessment. We suggest that a similar mating pattern is found in many lek-breeding hylid frogs in which male mating success is mainly determined by chorus attendance.