Meeting Abstract
The concept of a coevolutionary arms race has been widely-used to account for paired trait variation in vertebrate predators and their prey yet empirical confirmations of this explanation are few. Here we examine the applicability of the arms race analogy to interactions between venomous Northern Pacific Rattlesnakes and their main prey California ground squirrels by assessing evolutionary causes of parallel variation in snake venom activity and prey resistance across 12 snake and prey populations. We used in-vitro assays of venom protein function and resistance factor effectiveness to show that: 1) there is substantial geographic variation in both venom enzymatic activity and resistance factor effectiveness consistent with coevolutionary dynamics across geographically distinct populations in these traits. 2) Statistical analysis of local adaptation shows evidence of the effectiveness of snake venom to overcome squirrel resistance but not of squirrel resistance to snake venom composition. 3) The local adaptation of snakes to squirrels has a strong environmental component in that it only occurs between snakes and squirrels in populations at different elevations, demonstrating the possible contributions from local adaptation analyses that incorporate environmental structure into statistical models. Our results support the coevolutionary arms race as a general explanation for geographic variation in both animal venoms and prey resistance, because variation in squirrel resistance is likely responsible for variable selection on venom phenotypes, suggesting a tight evolutionary relationship between the two species. Adaptation by predators to environmentally-determined physiological variation in prey needs to be considered as a mechanism for the evolutionary diversification in predatory traits such as venom at the molecular level.
