Toad-Headed Lizard Phrynocephalus Forsythii (Squamata, Agamidae) As A Potential Ring Species Inferred From Population Genetic Differentiation

Speciation has never been directly observed in nature because it is a lengthy phenomenon. Although rare, ring species are an optimal natural example of speciation and can be identified through the assessment of the geographical conditions of their potential habitat Phrynocephalus forsythia is endemic to the Tarim Basin, which comprises the Taklamakan Desert and surrounded by mountains on three sides. This study aimed to determine whether P. forsythia had a ring-species-like divergence pattern through the characterization of the genetic features of 17 populations covering the major distribution of this species Species distribution modelling revealed that P. forsythii had a continuous circular distribution around the Tarim Basin Gene flow was observed in most adjacent populations except for two terminal populations of the ring, which exhibit the highest differentiation. Genetic distance and geographic distance were significantly correlated, indicating that the observed differentiation resulted from genetic variation gradually accumulating during population dispersion. Although our results do not definitively indicate that P forsythia is a ring species, our results indicate a ring-shaped diversification. This phenomenon elucidates the potential mechanism underlying speciation in the presence of gene flow, providing insight into this evolutionary process.