Evolutionary history of Podarcis tiliguerta on Corsica and Sardinia

Abstract

Background: Podarcis tiliguerta is a wall lizard endemic to the Mediterranean islands of Corsica and Sardinia. Previous findings of high mtDNA and morphological diversity have led to the suggestion that it may represent a species complex. Here, we analysed mitochondrial and nuclear markers (mtDNA, 3110 bp; 6 nDNA loci, 3961 bp) in P. tiliguerta sampled from thirty-two localities across Corsica and Sardinia.

Results: We find much greater intraspecific genetic divergence than between sister species of other Mediterranean island Podarcis, i.e., between P. lilfordi and P. pityusensis. We detected three mtDNA clusters in Corsica (North, South-East and South-West) and either two or three in Sardinia (North vs. South) depending on the clustering method. Only one or two nDNA groups were identified within each main island (again, depending on the method). A Bayesian time-calibrated multispecies coalescent tree was obtained from mtDNA and provided statistical support for a Miocene origin of the species (13.87 Ma, 95% HPD: 18.30-10.77 Ma). The posterior mean divergence time for the Corsican and Sardinian lineages was 12.75 Ma ago (95% HPD: 16.94-9.04 Ma).

Conclusion: The results support the evolutionary distinctiveness of Corsican and Sardinian populations and also indicate a lack of post-divergence migration despite periods of contact being possible. Further to this, species delimitation analyses of Corsican and Sardinian lineages provided statistical support for their recognition as distinct (sister) taxa. Our results provide new insights into the biogeography of the Mediterranean biodiversity hotspot, and contribute important findings relevant to the systematics and evolution of this speciose lizard genus.

Keywords: Corsica and Sardinia Islands; Lacertidae; Mitochondrial DNA; Nuclear DNA; Podarcis tiliguerta; Species tree.

Fig. 1

Sites at which Podarcis tiliguerta were sampled in Corsica, Sardinia and adjacent islands

Fig. 2

Overall genetic structure inferred from a) mtDNA and b) concatenated nuclear loci across the two main geographic regions used in this study. Mixture analyses were estimated by BAPS software. In the bar plot, vertical bars represent individuals and proportions of admixture, with colours corresponding to ancestral sources

Fig. 3

Nuclear haplotype networks for Podarcis tiliguerta

Fig. 4

Analyses of Bayesian phylogeographical and ecological clustering (BPEC): a) using mtDNA or b) RAG1 as example of nuclear DNA. Each coloured contour plot indicates a different phylogeographical clusters. The contour plots are centred at the ‘centre’ of each population cluster, and the coloured regions show the radius of 50% concentration contours around it. White arrows show the ancestral locations with the highest posterior probability for each island

Fig. 5

Mitochondrial populations tree chronogram estimated by *BEAST in P. tiliguerta. P. lilfordi and P. pityusensis are used as outgroups. Grey bars correspond to the 95% highest posterior density intervals for each divergence time