What leads to new species of hybridizing whiptail lizards?

Scientists better understand how and why hybridization leads to various evolutionary outcomes – such as increasing the genetic diversity of a species, versus creating an entirely new species – thanks to a study of a type of lizard that includes a large number of species that frequently hybridize. The results of the study indicate that the genetic distance between parental genomes is a key predictor of hybridization outcomes, and in particular the likelihood of new species resulting from hybridization in these animals. Hybridization between species – a phenomenon common to many taxa – can lead to a variety of results. It can, for example, increase the genetic diversity within a species or create completely new ones. In lizards, hybridization can lead to transitions from sexual to unisexual reproduction. However, when and why hybridization between divergent lines leads to these various results remains unknown. To better understand these questions, Anthony Barley and his colleagues used the North American Whiptail lizard, a genus that includes the greatest diversity of unisexual lineages among vertebrates, as a model system to assess possible evolutionary outcomes of hybridization. Orge et al. used a phylogenetic network approach to investigate which sexual species were the parental ancestors of unisexual hybrid lineages. Only above a certain level of genetic distance between parental genomes—when the time to divergence between species exceeded ~10 million years—did hybridization result in unisexual lizards, according to the results. “These results distinguish hybridization models that have not been tested before,” the authors state, “and suggest that evolutionary outcomes may be predictable.”

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