Genetic Population Structure of the Italian Wall Lizards Podarcis siculus (Squamata: Lacertidae): Insight From Nuclear DNA Markers

ABSTRACT Since the Quaternary, recurrent climatic oscillations have profoundly shaped species distributions across the Mediterranean basin, generating complex phylogeographic patterns through repeated cycles of range contraction and expansion. The Italian Peninsula, characterized by a highly heterogeneous topography and a mosaic of glacial refugia, has emerged as a hotspot of intraspecific genetic diversity. The Italian wall lizard (Podarcis siculus), a widespread species across the Italian Peninsula and adjacent islands, represents an excellent model for exploring these dynamics. Previous phylogeographic studies based on mitochondrial (mtDNA) and nuclear (nuDNA) markers have revealed a highly structured matrilineal organization, with several parapatric lineages and subclades, but have also highlighted weak differentiation in nuDNA, suggesting possible mito-nuclear discordance. In this study, we used multilocus nuclear microsatellite data to (i) evaluate whether the complex mtDNA phylogeographic structure is reflected in nuclear markers, or whether evidence of mito-nuclear discordance is present, and (ii) quantify admixture and gene flow among mitochondrial lineages. Our results reveal partial congruence between mtDNA and nuclear patterns, with evidence of both historical isolation and secondary contact among major clades. However, several populations exhibit substantial mito-nuclear mismatches, suggesting a history of asymmetric introgression and differential lineage sorting. These findings indicate that P. siculus experienced multiple phases of demographic expansion and secondary contact, consistent with Pleistocene-driven range dynamics, and that mito-nuclear discordance has played a significant role in shaping its current genetic landscape. This study underscores the importance of integrating multilocus nuclear data with mitochondrial evidence to disentangle the evolutionary processes driving complex phylogeographic patterns in Mediterranean taxa.