The dual benefits of synchronized mating signals in a Japanese treefrog

<p>In dense mating aggregations, such as leks and choruses, acoustic signals produced by competing male conspecifics often overlap in time. When signals overlap at a fine temporal scale, either completely or partially, the ability of females to discriminate between individual signals is reduced. Yet, despite this cost, males of some species produce calls that closely follow those of conspecifics, synchronizing signal production by deliberately overlapping their signals. Here, we investigate two non-mutually exclusive hypotheses of synchronized mating signals in a Japanese stream-breeding treefrog (Buergeria japonica): 1) increased female attraction to the chorus through acoustic constructive interference (the beacon effect hypothesis) and 2) reduced attraction of eavesdropping predators through perceptual manipulation (the eavesdropper avoidance hypothesis). Our results from field playback experiments on female frogs and eavesdropping micropredators (midges and mosquitoes) support both hypotheses. Signal transmission and female phonotaxis experiments suggest that synchronized calls are more attractive to females at a distance than unsynchronized calls. At the chorus, however, eavesdroppers are less attracted to calls that closely follow an initial call, while female attraction to individual signals is not affected. Therefore, synchronized signalling likely benefits male B. japonica by both increasing attraction of females to the chorus and reducing eavesdropper attacks. These findings highlight the complex nature of signal synchronization and how multiple interacting selective pressures likely promoted the evolution and maintenance of this behaviour.</p>