Untitled

Abstract

Many animal species use acoustic signals for social communication including attracting mates, defending resources and assessing risks. Nevertheless, a variety of ambient noise sources often interfere with sound communication and efficient decision making. In the present study we identified an exception to this generalization in a streamside species, the little torrent frog (Amolops torrentis) which communicates in an environment in which stream noise is always present. To show that stream noise can act as a biological signal which reflects the character of the microhabitat of the sender, we performed female phonotaxis experiments using synthetic male advertisement calls. Calls with high dominant frequency exceeding the ambient stream noise band and calls with lower dominant frequency centered at the frequency range of best hearing were used. The signal-noise ratio was varied by adding noise to each kind of call. We found that females prefer calls with high amplitude stream noise added to those with low amplitude stream noise added for both the high and low dominant frequency stimulus pairs; however, the sound of running water had no attractiveness in the absence of calls. These results show that stream noise can function as an information source by enhancing the attractiveness of calls in the torrent frog. Stream noise associates closely with rocks, topographies and vegetation; thus the sound of running water may provide useful information to signal receivers about variations in microhabitats and thereby act on sexual selection under some circumstances. These data therefore contribute to our understanding of how the perception of mate attractiveness in heterogeneous ecological environments can evolve.