Lost Sex in the Reptiles: Constraints and Correlations

Abstract

Reptiles are the only truly parthenogenetic vertebrates, making it especially fascinating to understand how and why some reptilian taxa have broken free of sexual reproduction. In this review we consider the evolutionary and genomic constraints, consequences, and ecological correlations of reptile parthenogenesis, and how this informs us more generally about the loss of sex in organisms. In reviewing the taxonomic distribution of parthenogenesis we find that some lineages are particularly likely to evolve parthenogenesis (e.g., teiid lizards) and others biased strongly against parthenogenesis (e.g., colubrid snakes). Moreover, all but one of the natural cases also involves hybridization. The geographical and ecological tendencies of parthenogenetic reptiles suggest a bias toward “open” environments, yet there are often surprisingly high levels of coexistence and niche overlap between parthenogenetic lineages and their related sexual forms. To the extent that these fascinating patterns can be deciphered we will learn much about the constraints and selective forces acting on the evolution of parthenogenesis in nature.