THE MECHANISMS OF SEXUAL SELECTION IN A LEK-BREEDING ANURAN, Hyla intermedia.

In lek mating systems, sexual selection is thought to operate through two main mechanisms: endurance rivalry and female choice. We investigated the role of these mechanisms in explaining variation in male mating success in a typical lekking anuran, the Italian treefrog, Hyla intermedia. The results suggested that both chorus attendance and calling quality may affect male mating success, and that selection on these traits may indirectly result in selection for males with higher-than-average body condition. Both generalized linear models (GLM) and cubic-spline regressions (CSR) showed a monotonic relationship between mating success and chorus attendance, suggesting open-ended directional selection on male chorus tenure. GLMs on call acoustic properties showed a significant association of mating success with several highly intercorrelated call temporal properties (i.e. call rate, pulse rate and call duration), but not with call spectral properties. In both cases, however, CSRs provided evidence that the relationships of the call properties with mating success are unimodal, with peaks close to (spectral properties) or above (temporal properties) the population means. As often observed in anurans, chorus attendance explained much more variation in mating success than did calling quality. However, contrary to what is often assumed, we argue that the important role of endurance rivalry does not reduce, but rather emphasizes, the role of female choice in sexual selection.