9509295 9521429 Brodie Brodie A critical element of many theories of evolutionary change is the idea that there is a "cost" to adaptation: increased adaptation in one trait necessarily restricts the potential for increased adaptation of some other traits. One way that costs of adaptation, or evolutionary tradeoffs, are thought to arise is through coevolutionary interactions. Predator-prey systems that represent many generations of reciprocal selection are ideal situations to test this explanation for the evolution of tradeoffs. Only one natural predator-prey system has provided population level evidence of increased ability to exploit prey evolving as a result of antipredator adaptations in the prey. Newts of the genus Taricha occur along the west coast of the United States and produce the neurotoxin tetrodotoxin (TTX), which is one of the most potent nerve toxins known. The only known predators resistant to this toxin are Thamnophis sirtalis that occur with, and feed on, the newts. Snake populations differ markedly in their resistance to TTX, and within resistant populations there is preliminary evidence suggesting that decreased locomotor performance accompanies increased resistance to TTX. This system provides an exceptional opportunity to study the costs of adaptation associated with arms race coevolution. This research will examine potential costs of adaptation in resistant and nonresistant populations of garter snakes. Locomotor performance and TTX resistance will be studied in each population, and the correlation between these traits will be used to assess tradeoffs. A phylogeny describing the evolutionary relationships between populations will be constructed and used to examine the historical evolution of both resistance and the tradeoff between resistance and performance. This approach will allow tests of alternative explanations for the evolution of tradeoffs. Examining the evolution of resistance to TTX is a first step to understanding how organisms survive in th e face of widespread and dangerous natural toxins.
