Priority of precedence: receiver psychology, female preference for leading calls and sexual selection in insect choruses

In species in which males display collectively, females may evaluate display features that arise specifically in groups in addition to basic features of signal energy. For example, in acoustic insects and anurans that chorus, males often adjust their song timing relative to neighbours, and females may pay attention to these adjustments in timing. Many laboratory studies show how males may delay the phase of their song rhythm with respect to a song stimulus such that they call just prior to the stimulus; similarly, females may choose a male whose song rhythm leads a neighbour by a brief interval. However, the importance of male phase adjustments and female attention to call order in actual choruses has remained poorly understood. We studied female choice in laboratory choruses in the bushcricket Ephippiger diurnus, a species with preferences for leading calls but also for longer calls and faster rhythms, features representing broadcast energy. Although chorusing males varied in all features, we found that females largely focused on call order. This overriding preference for call order may be reflected by the prevalence of male phase adjustment throughout the population, a feature that would have been subject to strong sexual selection. We found that the broadcast of leading calls within a chorus was not repeatable among males but rather shifted among the chorus participants. This observation too may reflect the strong selection imposed by female choice for call order, and it may have implications for the role of receiver psychology in the evolution of mate choice.