Group synchrony and alternation as an emergent property: elaborate chorus structure in a bushcricket is an incidental by-product of female preference for leading calls

Abstract

Many acoustic animals exhibit temporally structured chorusing, and in some cases, groups of calling males display elaborate forms of synchrony and/or alternation. Such temporal structure has traditionally been explained as an adaptation by which chorusing males preserve critical call features, maximize the attractiveness of their local group to females, or improve their ability to detect, evaluate, and/or evade rival males or predators. However, an alternative possibility is that synchrony and alternation simply emerge as incidental by-products of basic pairwise signal interactions between male neighbors. Thus, females may not be influenced by synchrony and alternation, and males may not benefit per se from the very chorus that they collectively produce. We studied chorusing in the bushcricket Ephippiger diurnus, a species that sings in both synchrony and alternation, by presenting natural and modified chorus stimuli to females in a series of playback tests. We found that females responded readily to the various stimuli, but we did not observe an elevated response to the natural chorus stimuli in any experiment or in any of the several E. diurnus populations tested. Our results demonstrate for the first time how elaborate forms of synchrony and alternation can represent emergent properties of choruses as opposed to specialized group displays that afford particular advantages to the individual singers.