Date of Award:

5-1-2005

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

Edmund D. Brodie Jr.

Committee

Edmund D. Brodie Jr.

Committee

Paul G. Wolf

Committee

Daryll B. DeWald

Committee

Michael E. Pfrender

Committee

Roger A. Coulombe

Abstract

I examined the ecology and physiology of tetrodotoxin (TTX) toxicity in the newt genus Taricha (family Salamandridae) to understand the forces that have shaped the adaptive evolution of TTX toxicity in this group. In particular, this work sought to explore how coevolution with a TTX-resistant predator (the garter snake, Thamnophis sirtalis) has shaped patterns of phenotypic diversity in TTX toxicity among populations of Taricha. I developed a set of techniques to directly measure levels of TTX in the skin of newts, and used those measurements to estimate the amount of TTX a snake predator would be exposed to upon ingestion of individual newts from a given population. I have shown that variation in gross toxicity among populations of Taricha results from variation in the amount of TTX present in the skin of newts, and that levels of TTX are highly variable within and among populations of newts. An investigation of the TTX toxicity of eggs and females of T. granulosa demonstrated that newts may also be using TTX as a defensive compound in eggs and that female newts appear to be investing TTX independently of other maternally invested egg resources. This work also demonstrates that TTX toxicity in Taricha may not result from bacterial symbiosis and that newts may be able to more directly manipulate or even synthesize the TTX present in their skin. Finally, I developed a functional model of the interaction between TTX toxicity in newts and TTX resistance in their snake predator to investigate patterns of phenotypic matching between these two species across most of their range of sympatry. This analysis demonstrated that coevolution between newts and snakes has been an important force in the adaptive evolution of both TTX resistance in snakes and TTX toxicity in newts. This analysis also revealed that coevolution between these taxa is strongly modulated by geographic structuring in populations of newts and snakes and that the strength of reciprocal selection between these species is highly variable across the range of their interaction.

Included in

Biology Commons

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