Genetic variation and differentiation in the lizard, Podarcis wagleriana (Reptilia: Lacertidae)

Abstract

Abstract The electrophoretic variation at 26 presumptive gene loci was investigated in populations of Podarcis wagleriana from Sicily, the Aegadian Islands, and the Aeolian Islands. For interspecific comparison, samples of the closely related lizard P. sicula from the same geographic area were also used. Population heterogeneity analyses carried out by the estimation of F -statistics and Nei's standard genetic distance, showed a high genetic homogeneity within P. sicula , but a noticeable genetic differentiation within P. wagleriana . In the latter species, Nei's D ranged from 0 to 0.212, and this is because the Aeolian populations were quite distinct from those inhabiting Sicily and the Aegadian Islands. Fixed differences identified at three loci ( Ck, Ada, Gp-4 ) contributed to a relatively high value of Nei's standard genetic distance between the two population groups ( D = 0.147). This value is very similar to those found comparing pairs of well-recognized biological species included in the genera Podarcis and Lacerta . Estimation of the time of evolutionary divergence shows that the Aeolian and Sicilian populations of P. wagleriana have been isolated geographically for a long time (0.7 Myr according to Nei's formula; 2 Myr according to Sarich's calibration), indicating evolutionary divergence at the species level. Based on genetic and biogeographic data, it is suggested the recognition of full specific status for the Aeolian populations, for which the name P. raffonei comb. nova (Aeolian wall lizard) is proposed. Electrophoretic data and comparative species distributions suggest that (1) Podarcis sicula recently colonized the Aeolian Islands, and (2) it has competed successfully with P. raffonei in this area, greatly reducing the range of the latter and causing the extinction of most of its populations. In fact, P. sicula is widespread in the Aeolian Archipelago, while P. raffonei is confined at present to one large island (Vulcano) and three tiny islands (Strombolicchio, Scoglio Faraglione, La Canna). This can be considered a classic example of competitive exclusion of a native form ( P. raffonei ) by a species accidentally introduced by man ( P. sicula ).