A genomic perspective on the origins, evolution and 2 adaptation of Galápagos iguanas

Island systems provide unique opportunities to explore the genomic basis of species diversification and novel trait evolution driven by adaptation to environmental challenges and exploitation of new ecological niches. Here we generate the first genomic sequences for the four Galápagos iguana species to show that they evolved in situ into the marine Amblyrhynchus and land Conolophus sister lineages on now submerged islands, following a single colonisation event approximately 13 million years ago, with evidence for recent inbreeding coincident with the timing of human settlement. Selection scans identified genes linked to traits facilitating adaption to the Galápagos environment, including specialised pigmentation phenotypes, as well as DNA damage and UV irradiation inflammation responses. These may contribute to adaptive enhanced cancer resistance, in relation to elevated UV exposure at equatorial latitudes. In the marine iguana, genes under positive selection are associated with their transition to underwater foraging, as well as their unique ability to repeatedly shrink and grow in body size. Our study provides insights into the origins and diversification of the iguanas and the molecular basis of adaptation to life in the Galápagos, facilitating future conservation genomic management of threatened iguanid populations.