Genomic insights into the biogeography and evolution of Galápagos iguanas.

Abstract

Galápagos iguanas are a monophyletic group endemic to the Galápagos archipelago, comprising the marine iguana Amblyrhynchus cristatus and three species of land iguanas: Conolophus subcristatus, C. pallidus and C. marthae. The biogeographic history of the land species in relation to their current distributions remains uncertain, in particular the origins of C. marthae, which is restricted to a small area of the northern part of Isabela Island. The classification of C. pallidus as a separate species has also been debated. We analyzed DNA sequences (RADseq) to reconstruct demographic histories of selected local populations of all Galápagos iguana species and estimate their divergence times within a multispecies coalescent framework. Our results indicate an early date for the colonization of Galápagos by iguanas, relative to island formation, at ca. 10 Mya, and support a recent split of C. marthae via allopatric speciation, after the emergence of Isabela Island, at ca. 0.57 Mya. We find contrasting demographic histories in C. marthae and the syntopic population of C. subcristatus, suggesting competitive interaction between these species. We also confirm that the divergence of C. pallidus from C. subcristatus is recent (0.09 Mya) and close in time to the split between populations of C. subcristatus from different islands. Our genetic data support recent census estimates indicating a relatively small current effective population size (N_e) in all the studied populations. Our findings shed light on the evolutionary history of Galápagos iguanas and emphasize the need for targeted conservation strategies.