Female choice and plasticity of male calling behaviour in the Pacific treefrog

Male Pacific treefrogs, Hyla regilla, use advertisement and encounter calls to regulate intermale spacing within breeding choruses. When either type of call produced by a neighbour is detected above a particular amplitude, a resident frog responds aggressively by producing encounter calls. These 'aggressive thresholds' differ for the two call types and are plastic: males rapidly resume advertisement calling (accommodate) following repeated presentation of these calls above their aggressive threshold. We tested the hypothesis that this plasticity is the result of female preference for the advertisement call over the encounter call. Female choice was tested in a two-speaker phonotaxis assay with alternating presentation of the two call types. Of the 12 females that met our criteria for demonstrating a phonotaxic response, each approached the speaker playing the advertisement call rather than the encounter call: This strong female preference for the advertisement call supports our hypothesis, and suggests that the-plasticity in male calling behaviour allows males to maximize the time spent in producing advertisement calls to attract a female by rapidly adjusting their aggressive behaviour to; changes in male spacing within choruses. (C) 1999 The Association for the Study of Animal Behaviour.