What leads to new species in whiptail lizard that hybridize?

Scientists better understand how and why hybridization leads to diverse evolutionary outcomes – such as increased genetic diversity in a species, versus creation of a species that’s wholly new – thanks to a study in a type of lizard that includes a large number of species that frequently hybridize. The study’s results point to genetic distance between the parental genomes as a key predictor of hybridization outcomes, and particularly of the likelihood of new species resulting from hybridization in these animals. Hybridization between species – a phenomenon common in many taxa – can lead to a variety of outcomes. It can, for example, increase the genetic diversity within a species or create whole new ones. In lizards, hybridization can result in transitions from sexual to unisexual reproduction. However, when and why hybridization between diverging lineages results in these diverse outcomes remains unknown. To better understand these questions, Anthony Barley and colleagues used the North American whiptail lizard, a genus that includes the highest diversity of unisexual lineages among vertebrates, as a model system to evaluate the possible evolutionary outcomes of hybridization. Barley et al. used a phylogenetic network approach to investigate which sexual species were the parental ancestors of hybrid, unisexual lineages. Only above a certain level of genetic distance between the parental genomes – when the divergence time between species exceeded ~10 million years – did hybridization result in unisexual lizards, the results show. “These results distinguish among models for hybridization that have not previously been tested,” say the authors, “and suggest that the evolutionary outcomes can be predictable.”