BRODIE III, Edmund D.; BRODIE, JR., Edmund D.; RIDENHOUR, B. J.; Indiana University; Utah State University; Indiana University: Reciprocal selection at the phenotypic interface of coevolution

Coevolutionary interactions between species depend upon a phenotypic interface of traits in each species that mediate the outcome of interactions among individuals. These phenotypic interfaces usually involve performance traits, such as locomotion or resistance to toxins, that comprise an integrated suite of physiological, morphological and behavioral traits. The reciprocal selection from species interactions may act directly on performance, but it is ultimately the evolution of these underlying components that shapes the patterns of coevolutionary adaptation in performance. Bridging the macroevolutionary patterns of coevolution to the ecological processes that build them therefore requires a way to dissect the phenotypic interface of coevolution and determine how specific components of performance in one species exert selection on complimentary components of performance in a second species. We present an approach for analyzing the strength of selection in a coevolutionary interaction, and for identifying which component traits of the phenotypic interface are critical to mediating coevolution. The approach is illustrated with data from a predator-prey arms race between garter snakes and newts that operates through the interface of tetrodotoxin (TTX) and resistance to it. TTX resistance in snakes is geographically and phylogenetically variable and is controlled in part by differences in sodium channel function. The evolution of snake sodium channel differences is attributable to selection through whole animal performance resulting from varying levels of TTX toxicity in prey.