Adaptive plasticity in calling site selection in grey treefrogs (Hyla versicolor)

Abstract

Calling behaviour is an essential component of gaining access to mates, and calling site selection may be an important component of effective communication. Environmental factors like microclimate, or the presence of competitors and predators often show seasonal or spatial variation, and behavioural plasticity that allows the caller to adjust to this variation may be adaptive. Prompted by the observation of across-season variation in elevated calling site use in our grey treefrog population, we formulated three hypotheses about their calling site choice and tested them using field observations and behavioural trials in the lab. We found that calling site selection is largely determined by local temperature regimes, and suggest that this temperature-based plasticity in calling site selection is adaptive because it allows males to increase their metabolic efficiency and mate attraction effectiveness. The mere presence of heterospecific competitors and predators did not affect calling site selection at the pond, but close proximity to a predator during behavioural trials did reduce calling activity. This suggests that grey treefrog males attend to the presence of predators, that they can assess the degree of risk associated with predator proximity, and that they can adjust calling behaviour adaptively to reduce the chances of being detected by a predator.