How diverse a snake needs to be? Genetic and venom variability shaping snake distribution on Brazilian islands

The molecular mechanisms of adaptive evolution are unclear. We still do not have a complete understanding of how complex evolutionary novelties are generated during the process of recent speciation. Venomous snakes isolated on islands are considered a powerful model to study the evolutionary processes that create the phenotypic diversity. The venom diversity of the Bothrops jararaca species-complex has been suggested to be strongly related with the species diets and geography. Populations of B. jararaca underwent several episodes of recent speciation on the continental island off the coast of Brazil. This repeated speciation process makes this species-complex an extreme case of repeated recent adaptation to distinct niches. In this study we evaluated whether the variability of venom of the B. jararaca complex can shed light on the evolutionary forces and mechanisms that shaped the island colonization process in this group. We generated venom profiles, as well as, we sequenced the gland transcriptome, the complete mitochondrial genome and anonymous loci for populations from the islands and the continent. Using population genetic tools, we tested the hypothesis of rapid venom diversification being driven by ecological speciation by adaptive evolution to different diets, or alternately, if the demographic history can explain better the venom differences among populations through genetic drift. Our results suggest that the high genetic and phenotypic variability of B. jararaca is probably the key factor that allows this group to successfully colonize several islands on the coast of Brazil.