Assessing evolutionary history and species boundaries in a polymorphic tropical lizard, the Aspidoscelis lineattissimus species complex (Squamata, Teiidae)

Identification of species boundaries within the genus Aspidoscelis is one of the most complex tasks in herpetological systematics due to the extensive morphological variation and complex evolutionary history involved. The whiptail lizard Aspidoscelis lineattissimus is a polymorphic species that inhabits tropical ecosystems over a wide region of western Mexico and is currently classified into four subspecies, A. l. exoristus, A. l. lineattissimus, A. l. lividus and A. l. duodecemlineatus. In this study, we used phylogenetic and coalescent-based approaches to disentangle the phylogenetic relationships among the subspecies of A. lineattissimus and to assess the level of differentiation between these subspecific taxa. We also inferred the divergence times and historical biogeography to reconstruct the evolutionary history of the A. lineattissimus complex. Three mitochondrial genes (ND4, 12S and 16S) and one nuclear exon (BACH1) were used, along with comprehensive sampling that included individuals representing the four subspecies. Coalescence analyses supported three well-differentiated lineages as independent evolutionary units, corresponding to A. l. exoristus, A. l. lineattissimus + A. l. lividus and A. l. duodecemlineatus, partially recovering the previous classification. Furthermore, phylogenetic analyses support three additional discrete lineages within A. l. duodecemlineatus. Finally, divergence time estimates and reconstructions of ancestral areas indicated that the origin and diversification of the five differentiated lineages within the A. lineattissimus complex was strongly associated with oscillations in sea level due to glacial/interglacial climatic fluctuations beginning in the Mid-Pliocene. Our research highlights the importance of phylogenetic studies within the genus Aspidoscelis to disentangle their evolutionary history and reveal hitherto underestimated diversity.