Costly help of audiovisual bimodality for female mate choice in a nocturnal anuran (Hyla arborea)

In nocturnal anurans, females often have to choose a mate in a sensory-challenging situation--noisy background and high density of potential mates. Multimodality can help female choice by improving mate choice accuracy or reducing time to choose. Here, we conducted 2 choice experiments in the European tree frog (Hyla arborea) to test this question in 2 sensory conditions of large or reduced difference between potential targets, the latter being a discrimination challenge for females. We examined female choice (target, time to choose) in 3 conditions: unimodal conditions with varying acoustic signals, multimodal conditions with nondiscriminating acoustic signals and varying visual signals, and multimodal conditions with varying both acoustic and visual signals. We find that females are less accurate and take more time to choose when targets are more similar. The use of 2 varying sensory modalities reduces latency to choose when targets largely differ. It improves mate choice accuracy when targets are more similar. This improvement is associated to a longer time to choose, suggesting a speed--accuracy trade-off, which is shown for the first time in a mate choice context. We also find that the presence of nondiscriminating acoustic cues is not helpful for mate choice. Finally, we show that females choose the high-quality stimulus more quickly and suggest that this temporal gain may be reinforced when targets are more similar. We discuss our results in relation to female sampling tactics and to the benefits and costs of multimodality. Copyright 2011, Oxford University Press.