Molecular Ecology (2007) doi: 10.1111/j.1365-294X.2007.03230.x © 2007 The Authors Journal compilation © 2007 Blackwell Publishing Ltd Blackwell Publishing Ltd Contrasting patterns of population subdivision and historical demography in three western Mediterranean lizard species inferred from mitochondrial DNA variation C. PINHO, D. J. HARRIS and N. FERRAND CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Campus Agrário de Vairão, 4485-661 Vairão, Portugal and Departamento de Zoologia e Antropologia, Faculdade de Ciências da Universidade do Porto, 4099-002 Porto, Portugal Abstract Pleistocene climatic oscillations were a major force shaping genetic variability in many taxa. We analyse the relative effects of the ice ages across a latitudinal gradient in the Western Mediterranean region, testing two main predictions: (i) species with historical distributions in northern latitudes should have experienced greater loss of suitable habitat, resulting in higher extinction of historical lineages than species distributed in southern latitudes, where the effects of the ice ages were not as drastic. This would be reflected in the obser- vation of lower diversity and number of differentiated lineages in northern areas. (ii) a sig- nature of demographic expansion following the climate amelioration should be obvious in northern species, whereas in the south evidence of long-term effective population size stability should be observed. We used as models three species of wall lizards (Podarcis bocagei, Podarcis carbonelli and Podarcis vaucheri) that replace each other along the study area. We investigated the patterns of mitochondrial DNA diversity and subdivision and obtained demographic parameter estimates for each species. Our results suggest that P. bocagei, the northernmost species, bears low genetic diversity, a shallow coalescent history and marks of a demographic expansion. In contrast, P. vaucheri, the species with a south- ernmost distribution, shows deeper coalescence events, complex geographical substructure and no evidence for population growth. The species with an intermediate distribution, P. carbonelli, shows average levels of diversity, substructure and population growth. Taken together, these results conform to our main predictions and are explained by a differential influence of the ice ages on distinct latitudes. Keywords: demography, glaciations, Iberian Peninsula, latitudinal gradient, North Africa, phylo- geography, Podarcis , population structure Received 5 September 2006; revision received 22 October 2006; accepted 6 November 2006 Introduction Pleistocene climatic oscillations are generally believed to have played a major role in shaping genetic diversity across a wide number of taxa (Hewitt 1996, 1999). In recent years, following the rise of phylogeography as a formal discipline (Avise et al . 1987; Avise 2000), a large number of surveys of genetic variation have disclosed patterns of genetic subdivision related to isolation in glacial refugia during the cold stages and demographic and geographical expansions following the retreat of the ice sheets (Taberlet et al . 1998; Milá et al . 2000; Lessa et al . 2003). Although this paradigm is one of the most consensual in modern biogeography, some aspects are still under debate, namely whether glacial times had an as severe influence on the historical distributions of nontemperate species as has been demonstrated for Europe and North America (e.g. Willis & Whittaker 2000). In this context, Lessa et al . (2003) investigated the effects of the Pleistocene glacial ages across the American continent by exploring the genetic signatures of postglacial demographic expansion in mammal populations from both North America and Amazonia. These signs of expansion were found to be present in North Correspondence: Catarina Pinho, Fax: +351252661780; E-mail: catarina@mail.icav.up.pt