The Atlas mountains as a biogeographical divide in North-West Africa: evidence from mtDNA evolution in the Agamid lizard Agama impalearis.

Since the early Miocene there have been several physical events within NW Africa that are likely to have had a major impact on its faunal diversity. Phylogeographical studies will shed new light on the biogeography of the region. We analysed mitochondrial DNA diversity in the agamid lizard Agama impalearis (also called A. bibronii) based on sequences from mitochondrial genes with very different evolutionary rates (16S rRNA and ND2). Well-supported topologies of rooted maximum parsimony trees (with a Laudakia outgroup) and unrooted haplotype networks indicated two major clades with similar branch lengths. These clades have non-overlapping distributions representing respective areas to the North and West and South and East of the Atlas mountain chain and each could be given full species recognition. Nested clade analyses indicate that historical and possible present-day allopatry account for the primary phylogeographic pattern. Further evidence is provided by the estimated timing of cladogenesis, based on calibration of evolutionary rates in the ND2 gene of another continental Agamid. Sequence divergence between clades corresponds to 8.5-9.4mya, coinciding with the main period of orogenic uplift of the Atlas. Additional evidence of cladogenesis by allopatric fragmentation is also detected within the North/West Atlas clade, although contiguous range expansion is the most predominant explanation of more recent phylogeographic effects in this species. Miocene vicariance mediated by the Atlas may provide a general explanation of intra- and interspecific biogeographical patterns in NW African species.