Responses of tadpoles to hybrid predator odours: strong maternal signatures and the potential risk/response mismatch

Abstract

Previous studies have established that when a prey animal knows the identity of a particular predator, it can use this knowledge to make an 'educated guess' about similar novel predators. Such generalization of predator recognition may be particularly beneficial when prey are exposed to introduced and invasive species of predators or hybrids. Here, we examined generalization of predator recognition for woodfrog tadpoles exposed to novel trout predators. Tadpoles conditioned to recognize tiger trout, a hybrid derived from brown trout and brook trout, showed generalization of recognition of several unknown trout odours. Interestingly, the tadpoles showed stronger responses to odours of brown trout than brook trout. In a second experiment, we found that tadpoles trained to recognize brown trout showed stronger responses to tiger trout than those tadpoles trained to recognize brook trout. Given that tiger trout always have a brown trout mother and a brook trout father, these results suggest a strong maternal signature in trout odours. Tadpoles that were trained to recognize both brown trout and brook trout showed stronger response to novel tiger trout than those trained to recognize only brown trout or only brook trout. This is consistent with a peak shift in recognition, whereby cues that are intermediate between two known cues evoke stronger responses than either known cue. Given that our woodfrog tadpoles have no evolutionary or individual experience with trout, they have no way of knowing whether or not brook trout, brown trout or tiger trout are more dangerous. The differential intensity of responses that we observed to hybrid trout cues and each of the parental species indicates that there is a likely mismatch between risk and anti-predator response intensity. Future work needs to address the critical role of prey naivety on responses to invasive and introduced hybrid predators.

Keywords: generalization; hybrid predators; invasive species; learning; predator recognition; risk assessment.

Figure 1.

Mean (±s.e.) proportion change in line crosses for woodfrog tadpoles conditioned to tiger trout odour with alarm cue (black bars) or control water (white bars) and subsequently exposed to tiger trout, brown trout, brook trout, rainbow trout or goldfish odour. Different letters indicate significant differences at α = 0.05 based on Tukey post-hoc tests.

Figure 2.

Mean (±s.e.) proportion change in line crosses for woodfrog tadpoles in response to tiger trout odour (black bars) or goldfish odour (white bars). Tadpoles were previously conditioned twice with tadpole alarm cues to recognize brown trout (2 × (TP + BnT)), twice to recognize brook trout (2 × (TP + BkT)) or once to recognize brown trout and once to recognize brook trout ((TP + BnT) + (TP + BkT)).