Parallel Evolution of a Gene Family in Two Vertebrate Radiations

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The evolutionary paths available to a population of organisms may depend on its history. For example, certain genetic changes may be unlikely to occur unless other genetic changes are already in place. Tracing the evolutionary history of traits that involve many genetic changes is crucial for understanding how organisms meet new challenges imposed by the environment. This project will examine the evolution of a group of genes that allow predators to cope with toxins produced by their prey. By asking whether evolutionary changes tend to occur in a particular order in this group, this work will determine to what extent evolution is limited by the ancient history of a species. This work may also have practical applications; for example, understanding how predators evolve to cope with toxic prey may aid in the design of more effective pain medications or pesticides, many of which affect the same genes as prey toxins. Understanding the evolution of complex traits involving many genes is a central challenge in evolutionary biology. Gene families, groups of similar genes that are the products of ancient gene duplications, provide a tractable model for the genetic basis of complex phenotypes, as they may both make similar contributions to the expression of a trait and respond to selection in similar ways. This project will combine analysis of published genomes and high-throughput sequencing to trace the evolutionary history of the voltage-gated sodium channel (Nav) gene family in snakes, lizards, and birds. Nav genes have evolved to allow consumption of highly toxic prey in several species of snakes, but the evolutionary processes allowing such repeated evolution are poorly understood. The Nav family will be sequenced in a large number of species to determine 1) whether ancient evolutionary changes in lizards predisposed the evolution of toxin resistance in snakes; 2) whether the Nav family evolves in a predictable manner in lineages of birds that consume toxic prey; and 3) what molecular mechanisms underlie observed evolutionary patterns in the gene family. The results of this work will help to disentangle the roles of historical contingency and predictability in molecular evolution.