Song recognition in female bushcrickets Phaneroptera nana.

Unlike most acoustic systems evolved for pair formation, in which only males signal, in many species of phaneropterine bushcrickets both sexes sing, producing a duet. We used the duetting species Phaneroptera nana as a model to explore the cues in the male's song that elicit the female's phonoresponse. Different synthetic male songs (chirps containing 2-6 pulses) were presented to Ph. nana females, and their acoustic responses were recorded. The threshold of the female response is lowest at 16 kHz (best frequency), coinciding with the dominant frequency of the male song. The specific amplitude pattern of consecutive pulses in the song of the male is not a critical factor in his signal. That is, songs with both a normal and a reversed order of pulses equally elicit a female response. By systematically deleting pulses from the synthetic male chirp, we found that at least two pulses are needed to elicit a female reply. Under no-choice conditions, increasing the number of pulses did not result in a higher probability of response and did not change the latency of the response; i.e. two pulses are necessary and sufficient to elicit a female response. The range of pulse duration that elicits a female response is 0.2-25 ms, and the inter-pulse silent interval ranges from 5 to 30 ms.