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
Résumé
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.