LEHMAN, E.M.; Indiana University, Bloomington: Tetrodotoxin as a maternally-endowed defense against egg predation in the rough-skinned newt, Taricha granulosa

Antipredator defenses include behaviors to evade capture, physical structures to deter predation, and noxious or toxic chemicals aimed at predators. While adults are often well protected, early life history stages (e.g., eggs) often are more vulnerable. In these cases, parents may provide defenses either through their behavior or through chemicals provided to the embryo. Nest defense behaviors have been well studied, but relatively little is known about chemical defenses in eggs. Studying the defenses of early life history stages is particularly interesting because of the influence early survivorship can have on population growth rates. Rough-skinned newts, Taricha granulosa, possess tetrodotoxin (TTX), a neurotoxin that inhibits the propagation of nerve signals, leading to paralysis and potentially death in most organisms that ingest it. TTX acts as a chemical defense against predatory garter snakes in adults, and is also present in newt eggs. Field work has shown that caddisfly larvae prey upon newt eggs, despite the presence of TTX. Because adults do not defend eggs, TTX may be eggs� only defense against predation. It was previously unknown to what degree caddisfly larvae consume eggs of varying toxicity and how TTX affects them. Here we report the results of several studies, including field and laboratory studies of predation as a function of egg toxicity, and the influence of predator cues on developing newt embryos. The relationship between newt eggs and their caddisfly predators, the effect of TTX on this relationship, and the potential for co-evolutionary interactions in this system will be discussed.