Female and male phonotactic responses and the potential effect of sexual selection on the advertisement calls of a frog

The outcome of sexual selection acting on a given sexual trait depends on the interaction between the strength, direction and form of both inter- and intrasexual selection processes. Therefore, determining female choice and male–male competition is necessary to gain a better understanding of how sexual selection acts on sexual traits. Anuran males produce advertisement vocalizations to attract females and to maintain other males at distance, providing a convenient opportunity to test the combined effect of inter- and intrasexual selection. Our main objective was to test experimentally potential effects of female choice and male–male competition and their interaction when acting as selective agents on the advertisement vocalizations of the rosy ground frog, Eupsophus roseus . We performed phonotaxis experiments on females and males and determined their behavioural responses to artificial signals synthesized based on the distribution of natural calls. The main results suggest that females' preference would favour vocalizations having lower frequencies and a harmonic composition in which the main harmonics of vocalizations have similar amplitudes. These preferences suggest that females could exert negative directional sexual selection on the frequency and stabilizing selection on the amplitude ratio. The responses of males were variable, suggesting that this type of male–male competition may not result in intrasexual selection favouring specific values of advertisement vocalizations. The occurrence of no clear preferences in males may result in a decrease in the potential effect of females' preferences, which could further contribute to variability in spectral components of calls.