Understanding Species Boundaries that Arise from Complex Histories: Gene Flow Across the Speciation Continuum in the Spotted Whiptail Lizards.

This article focuses on resolving the complex systematics and evolutionary history of the spotted whiptail lizards (genus Aspidoscelis, A. gularis complex), a group notable for extensive hybridization and the generation of unisexual species through hybrid speciation. Using reduced representation genomic data and integrative phylogenetic and population genetic methods, the study identifies three primary genetic lineages structured by geography and environment, with evidence of historical and ongoing gene flow complicating species delimitation. The authors propose a two-species taxonomy reflecting evolutionary independence supported by genetic, ecological, and biogeographic data, while recognizing additional genetically and morphologically distinct populations as subspecific or incipient lineages. This work clarifies the ancestry of unisexual whiptail species derived from these lineages and illustrates how modeling evolutionary processes can inform species boundaries in groups with reticulate histories and rapid diversification.