Meeting Abstract
The acoustic advertisement signals of many animals comprise a single sound repeated in a monotonous fashion. Multi-element signals, in which sounds with different acoustic parameters are produced closely together in time, are observed in a wide diversity of species across taxonomic groups. While increasing signal complexity may communicate greater information content, it is unclear what factors might effect the evolution of increasing signal complexity. In this study, we tested the hypothesis that acoustic preferences exhibited by females during mate-choice might constrain the evolution of increased call complexity. In a species where males produce only simple trilled calls (Hyla versicolor), we presented females with a choice between a natural, single-element call and an artificial, two-element signal. Artificial signals were generated by appending a computer-synthesized tone-burst to a normal trill. We were specifically interested in the main and interaction effects of: 1) the position of the artificial appendage relative to the trill; 2) the duration of the trill; 3) the duration of the appendage; 4) and the silent interval (SI) between the two call elements on preferences. The results of this study confirm that two-element signals with following appendages were generally attractive, but especially so when the duration of the trill is short. We observed interaction effects between the appendage position and both the SI and the duration of the appendage. In a leading position, longer appendages and appendages with a longer SI resulted in particularly unattractive multi-element calls. We conclude that receiver psychology is likely to be an important constraint on the evolution of increasing signal complexity. The generality of our results requires additional comparative studies of species with single-element signals.
