Population genetics of a colonizing lizard: Loss of variability in introduced populations ofPodarcis sicula

Abstract

Abstract. Allozyme electrophoresis was used to study the genetic variability (proportion of polymorphic loci and heterozygosity) in insular populations (Corsica, Elba, Montecristo, Marettimo, Pantelleria) of the lacertid lizard Podarcis sicula. These populations were presumed to have originated from episodes of accidental anthropogenic introduction. In order to test the hypothesis of a man-aided colonization and to provide comparative data, heterozygosity and polymorphism were also estimated in autochthonous populations of P. sicula from the Italian peninsula and Sicily. In each case, the presumed introduced population showed levels of genetic variability significantly lower than those detected in the autochthonous ones. Very little genetic differentiation was found among native and presumed colonist populations, Nei's standard genetic distances ranging from 0.001 to 0.009. These results strongly support the hypothesis that P. sicula was only recently introduced to the studied islands, and provide additional evidence of reduced genetic variability due to founder effect in insular populations originating from episodes of human transportation.

Molecular characterization of native (Italy) and introduced (USA)Podarcis siculapopulations (Reptilia, Lacertidae)

“…The original native populations of P. sicula show relatively high levels of genetic variation, as scored by Capula (1994), and this is confirmed by the mitochondrial patterns in the present research. On the basis of the few specimens assayed, the two introduced populations display a very low level of nucleotide variation.…”

“…In the smallest islands of the Tyrrhenian and Adriatic seas several insular populations had been separated at the subspecific level (see Lanza, in Amori et al, 1993, for an updated list): their taxonomy is worthy of reconsideration and most of them can probably be synonymized with either campestris, sicula, or cettii (see e.g., Corti et al, 1989, Abstract in 1 st World Congr. of Herpetol., Canterbury; Capula, 1994).…”

“…Non-native populations are known in continental Spain, Minorca Is., France, and western Turkey (reviewed in Capula, 1994). In North America, P. sicula populations have been established in Philadelphia (PA), Topeka (KS) and on Long Island (NY) (Behler & King, 1979;Conant & Collins, 1991).…”

“…From the ecological point of view, P. sicula has proven that it can spread very rapidly as well as successfully outcompete autochthonous lizards after introduction, as in Aeolian islands (Sicily), where the native P. raffonei is severely endangered (Capula, 1992(Capula, , 1994. Both of the assayed American populations (KS and NY) have also spread rapidly.…”

Do island populations have less genetic variation than mainland populations?

“…In a similar vein, introduced populations typically have lower levels of genetic variation than native ones within several species of lizards (Taylor & Gorman, 1975;Gorman et at., 1978;Capula, 1994), land snails (Selander & Kaufman, 1973;Johnson, 1988), insects (Bryant et a!., 1981;Gasperi et a!., 1991) and plants (Schwaegerle & Schaal, 1979;Clegg & Brown, 1983;Barrett & Husband, 1989;Novak & Mack, 1993). Stone & Sunnucks (1993) found a pattern of reducing genetic variation with founder effects as a gall wasp spread across Europe.…”