Evolutionary relationships of Podarcis lizards from Sicily and the Maltese Islands

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Abstract
The electrophoretic variation at 26 presumptive gene loci was investigated in populations of the closely related species Podarcis sicula, P. wagleriana, P. raffonei, and P. filfolensis. Low values of proportion of polymorphic loci (P) and mean observed heterozygosity (Ho) were found in P. sicula (P= 0.10; Ho= 0.016), P. wagleriana (P= 0.13; Ho= 0.029), and P. raffonei (P= 0.08; Ho= 0.017), while higher levels of genetic variability were observed in P. filfolensis (P= 0.17; Ho= 0.054). In the latter species, a multiple regression analysis was carried out in order to analyse the geographic correlates of P and Ho. The results of this analysis were consistent with the predictions of the time-divergence theory of variation, supporting the conclusion that directional selection is the main force eroding genetic variation on small islands. Intraspecific values of Nei's (1972) standard genetic distance were relatively low in P. sicula (average D= 0.024), P. wagleriana (average D= 0.004), and P. filfolensis (average D= 0.012), while higher in P. raffonei (D= 0.040). The lizards from Pantellena Island, which were considered by BISCHOFF (1986) to be very similar to P. filfolensis from Malta on the basis of a superficial analysis of the coloration pattern, were shown to actually belong to P. sicula. This confirms that the range of P. filfolensis only includes the Maltese Archipelago, Linosa Island, and the islet of Lampione. Surprisingly, the samples of P. filfolensis from the Pelagie Islands (Linosa and Lampione) were very similar to those from the Maltese Archipelago (average D= 0.016). This could be explained by rafting or anthropogenic introduction of P. filfolensis on Linosa and Lampione. Podarcis wagleriana and P. raffonei were genetically related (average D= 0.152), confirming the results of previous electrophoretic investigations. Podarcis filfolensis, though showing some morphological affinity with P. wagleriana, was genetically highly differentiated from this latter species (average D= 0.526), while being more similar to P. sicula (average D= 0.306). This indicates a close relationship between P. sicula and P. filfolensis, suggesting that P. sicula and P. filfolensis probably diverged from a common ancestor, and that the apparent similarity between P. filfolensis and P. wagleriana could be merely due to morphological convergence.