The persistence of Pliocene populations through the Pleistocene climatic cycles: evidence from the phylogeography of an Iberian lizard

Ancient climatic fluctuations have caused changes in the demography and distribution of many species. The genetic differentiation between populations of the same species and of sister species is often attributed largely to the more recent Pleistocene fluctuations. Recent interpretations, which implicate earlier episodes, have proved controversial. We address the timing of genetic divergence in the Iberian lizard Lacerta schreiberi by studying the phylogeography of the cytochrome b sequence. The species has a remarkable morphological uniformity, yet our evidence suggests that earlier events in the Pliocene initiated the main divergence between populations. This interpretation implies that the different populations survived through the Pleistocene in separate localities. This conclusion is robust to different molecular clock calibrations. The persistence of earlier differentiation through the Pleistocene has wide implications for our understanding of Pleistocene refugia in this species and, by extension, to the biogeography of the whole region.