Salamanders breeding in subterranean habitats: local adaptations or behavioural plasticity?

The exploitation of novel habitats requires the expression of specific behaviours. This may occur through both behavioural plasticity and local adaptations, but assessing the relative role of these processes is challenging. Animals colonizing underground environments are exposed to strong selective pressure: epigeous species using caves during one or more phases of their life cycles can help to understand mechanisms allowing cave exploitation. The fire salamander (Salamandra salamandra) may breed both in cave springs and in epigeous streams. We compared predation performance of larvae from cave and stream populations, and assessed whether local adaptations or behavioural plasticity (or both) improve predation in underground environments. We performed a behavioural experiment about prey detection and capture. We collected larvae from both caves and streams, and reared them under contrasting conditions: underground and outdoor. In the darkness, we tested two measures of predation performance of larvae: time of head turning towards the prey and frequency of prey capturing. We used an information-theoretic approach to assess the relative support of potential mechanisms (adaptations vs. plasticity). Both cave and stream larvae were able to detect and capture prey in the darkness. Larvae born in caves captured prey with higher success than those from streams. Acclimatization to underground conditions did not improve predation performance, suggesting that plasticity plays a minor role. This study indicates that the exploitation of underground environments leads to behavioural local adaptations, allowing an improved predation performance in environments where prey are both scarce and difficult to detect.