The evolution of viviparity opens opportunities for lizard radiation but drives it into a climatic cul-de-sac

Aim Evolutionary radiations into novel areas or niches require innovative adaptations. However, rapid subsequent changes in these novel conditions might demand rapid re-adaptations to secure population persistence and prevent extinction. We propose that reptilian viviparity (live birth) is consistent with such a scenario. Using the Liolaemus lizard radiation, we investigate the hypotheses that historical invasions of cold climates have been permitted by transitions to viviparity, and that this parity mode is irreversible. Then, we investigate whether these combined factors restrict viviparous lizards to cold climates, and hence, whether viviparous species are particularly threatened by climate change. Location South America. Methods We employ phylogenetic analyses to investigate evolutionary transitions in reproductive modes and their consequences for environmental restrictions in viviparous lizards. We then employ climatic projections to predict the impact of climate change on the future persistence of these organisms. Results The oviparity-to-viviparity transition is consistently associated with colonization of cold climates, and appears to be irreversible. Since viviparity seems less viable (compared with oviparity) in warm climates, species that evolve viviparity in cold climates are likely to remain adaptively constrained to such environments. Therefore, upward-poleward advances of climate warming will cause severe shifts and contractions of viviparous species ranges, threatening major extinctions over the next half century. Main conclusions Viviparity has been largely responsible for the successful radiation of Liolaemus into cold climates, but since this adaptation is predominantly viable in these environments and is unlikely to re-evolve into oviparity, viviparity may prove to be an evolutionary dead-end for lizards facing rapid climate change.