13. Mitochondrial phylogeny of the Darevskia saxicola complex: two highly deviant evolutionary lineages from the easternmost part of the range

The rock lizards of the Darevskia saxicola complex are found exclusively in the west of the Greater Caucasus and in southern Crimea. The earliest split within this group occurred between D. saxicola from the northern and D. brauneri from the southern slopes of the Greater Caucasus, followed by the split between D. brauneri and the Crimean D. lindholmi, and the expansion of D. saxicola to the westernmost slopes of the Greater Caucasus. We collected nominal D. brauneri from the two easternmost populations of the species range: the valleys of the Tekhuri and Enguri rivers in Georgia. Analysis of mitochondrial DNA showed that the lizards from both valleys are deeply differentiated from each other and from previously characterised D. brauneri. Lizards from Tekhuri keep a basal position within the clade D. saxicola (excluding D. praticola), and lizards from Enguri are closer matrilineally to the northern Caucasian D. saxicola than to either of the populations of nominal D. brauneri. Tekhuri lizards have broader heads and more small scales between the inner and outer rows of supraoculars than the other populations of the group. We suggest that the taxonomy of the group requires revision, considering the multiple deeply divergent mitochondrial lineages and introgressive gene flow between the continental populations of nominal D. saxicola and D. brauneri. The D. saxicola complex in the Caucasus resembles a “ring species” arrangement as described for other taxa and mountain regions.