EVOLUTIONARY GENETICS OF THE INSULAR LACERTID LIZARD PODARCIS-TILIGUERTA - GENETIC-STRUCTURE AND POPULATION HETEROGENEITY IN A GEOGRAPHICALLY FRAGMENTED SPECIES

Podarcis tiliguerta is an insular Mediterranean lacertid lizard endemi c to Corsica, Sardinia and many neighbouring small islands. The geneti c structure and population heterogeneity of the species were studied b y means of allozyme electrophoresis at 20 presumptive gene loci. The o bserved heterozygosity (H-o) decreases southwards towards more arid cl imatic regimes. No severe reduction in genetic variability was found i n samples from the tiny satellite islands, except for a population inh abiting a very small island off the south-western coast of Sardinia (M eli Island), in which about 80 per cent of the genetic variability was lost. Population heterogeneity analysis carried out by the estimation of Wright's F-statistics demonstrated substantial genetic differentia tion among populations. The value of F-ST (0.460) exceeds values known for other lizard species. F-statistics and genetic distance data show that genetic variation is distributed into three geographically coher ent population groups. The first group includes populations from the n orthern part of the range (Corsica), the second includes populations f rom the small islands off the south-eastern coast of Corsica (Cerbical e and Lavezzi), and the third comprises populations from the southern part of the range (Sardinia and Meli Island). The pattern of genetic v ariability and the apparent clinal variation of alleles at a few loci (Idh-1, Gapd, Gpi) indicate that the subdivided genetic structure of P . tiliguerta is moulded by the interplay of stochastic processes and a gents selectively affecting allele frequency changes.