EVOLUTIONARY RELATIONSHIPS OF PODARCIS LIZARDS FROM SICILY AND THE MALTESE ISLANDS

The electrophoretic variation at 26 presumptive gene loci was investig ated in populations of the closely related species Podarcis sicula, P. wagleriana, P. raffonei, and P. filfonesis Low values of proportion o f polymorphic loci (P) and mean observed heterozygosity (H-o) were fou nd in P. sicula (P = 0.10; H-o = 0.016), P. wagleriana (P = 0.13; H-o = 0.029), and P. raffonei (P = 0.08; H-o = 0.017), while higher levels of genetic variability were observed in P. filfolensis (P = 0.17; H-o = 0.054). In the latter species, a multiple regression analysis was c arried out in order to analyse the geographic correlates of P and H-o. The results of this analysis were consistent with the predictions of the time-divergence theory of variation, supporting the conclusion tha t 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. wagl eriana (average D = 0.004), and P. filfolensis (average D = 0.012), wh ile higher in P. raffonei (D = 0.040). The lizards from Pantelleria Is land, 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 Ar chipelago, Linosa Island, and the islet of Lampione. Surprisingly, the samples of P. filfolensis from the Pelagie Islands (Linosa and Lampio ne) were very similar to those from the Maltese Archipelago (average D = 0.016). This could be explained by rafting or anthropogenic introdu ction of P. filfolensis on Linosa and Lampione. Podarcis wagleriana an d P. raffonei were genetically related (average D = 0.152), confirming the results of previous electrophoretic investigations. Podarcis filf olensis, though showing some morphological affinity with P. wagleriana , was genetically highly differentiated from this latter species (aver age D 0.526), while being more similar to P. sicula (average D = 0.306 ). This indicates a close relationship between P. sicula and P. filfol ensis, suggesting that P. sicula and P. filfolensis probably diverged from a common ancestor, and that the apparent similarity between P. fi lfolensis and P. wagleriana could be merely due to morphological conve rgence.