Developmental window of response to predator chemical cues in rough-skinned newt embryos

Abstract

1. Many organisms are able to change their behaviour and/or morphology in response to the threat of predation. In some species, the ability to respond to predation cues may be limited to certain developmental time windows. 2. Here we examined the ability of rough-skinned newt (Taricha granulosa) embryos to respond to chemical cues from predatory caddisfly larvae when the timing of exposure varied. 3. We found that newt embryos hatch significantly earlier and at a significantly smaller size when exposed to chemical cues from caddisfly larvae. Further, newt embryos only responded when embryos were exposed to chemical cues from the first day of development. This developmental window of responsiveness corresponds with the phenology of caddisfly larvae and eggs in their natural habitat, where the presence or absence of caddisfly larvae when eggs are laid it indicates whether or not eggs are at risk of caddisfly predation. 4. Differences in response among newt embryos from different families and populations were also detected, although the factors responsible for these differences are unclear. 5. Newt response to predator exposure was not correlated with the amount of the potent neurotoxin tetrodotoxin in eggs, indicating that tetrodotoxin is not the only defence mechanism available to embryos. Further, the observed population and family differences in responses to cues are not likely to be related to differences in toxicity. © 2007 The Authors.