Phylogeny of the side-blotched lizards (Phrynosomatidae:Uta) based on mtDNA sequences: support for midpeninsular seaway in Baja California.

We investigated the phylogenetic relationships of western North American Side-blotched lizards, genus Uta, using mitochondrial DNA partial gene sequences from cytochorme b and ATPase 6. Uta stejnegeri appeared basal in our tree followed by U. palmeri. Uta stansburiana from the islands of Angel de la Guarda, Mejia, and Raza formed the next clade, followed by U. antiqua and other populations of U. stansburiana. These relationships suggest that the populations on the Angel de la Guarda island block should be recognized as a distinct species. Remaining populations of U. stansburiana formed two clades, corresponding to the northern and southern Baja California peninsula. Uta stellata and U. squamata occurred within the northern and southern clades, respectively. The discontinuity requires a long-lasting isolation, the only reasonable explanation being a former midpeninsular seaway. Correlations between our cladogram and magnetic anomalies in the Gulf of California date formation of the seaway at 1 million years ago.