The evolutionary origins of the parthenogenetic lizard Aspidoscelis tesselatus.

Most vertebrate species reproduce sexually. The whiptail lizards (Aspidoscelis) are a notable exception; at least 11 of the 45 recognized species are parthenogenetic. Here, we focus on one such species (Aspidoscelis tesselatus) as a case study to understand how parthenogenetic species originate and evolve. Using genome-wide sequence data and ecological niche modelling, we find that A. tesselatus likely arose from a single hybrid speciation event between A. scalaris and A. marmoratus less than 500,000 years ago. The geographic ranges of A. tesselatus and its parental species overlap currently, and niche modelling shows this zone of sympatry was even broader during the period when A. tesselatus likely formed. We additionally show evidence that A. tesselatus has a dynamic genome post-formation, with de novo mutations, introgression, and double-strand break associated events all contributing to variation within the species. These results show that asexual lineages can continue to be shaped by ongoing genomic and ecological dynamics, illuminating the processes that influence transitions in reproductive mode.