Intrinsic Reproductive Isolation among Ecologically Divergent Anolis Lizards

The evolution of reproductive isolation lies at the core of our modern concept of species. Despite this central importance, study of the evolution of reproductive isolation is largely limited to a set of laboratory amenable species. When shallowly divergent populations are associated with different habitats, extrinsic isolation is often assumed to play a major role. Because this type of isolation is environmentally mediated it can be ephemeral, for instance, if habitats change in response to climate. In contrast, intrinsic isolation is heritable and therefore loss of this type of isolation requires genetic changes in one or both populations. We performed a hybridization and backcross experiment to test for and characterize intrinsic reproductive isolation between two recently diverged, ecologically differentiated populations of Anolis lizards. We find evidence of substantial intrinsic isolation that appears to operate at the postmating, prezygotic phase. Our findings suggest that intrinsic isolation may play a substantial role in the maintenance of shallow, yet ecologically divergent, lineages.