Phenetic Relationships among Populations of Podarcis Sicula and P. Melisellensis (Sauria: Lacertidae) from Islands in the Adriatic Sea

Abstract

Clover, R. C. (Department of Biology, California State University, Long Beach, California 90840) 1979. Phenetic relationships among populations of Podarcis sicula and P. melisellensis (Sauria: Lacertidae) from islands in the Adriatic Sea. Syst. Zool. 28:284-298.-Thirtyone island populations of Podarcis sicula and P. melisellensis from Yugoslavia were examined to determine phenetic similarities based on means of 15 characters. Both cluster analysis and multidimensional scaling (MDS) revealed the following patterns of variation: 1) the two species formed distinct groups; 2) within each species, OTUs from northern and southern islands grouped separately; 3) within P. melisellensis, OTUs from small islands tended to resemble other small island OTUs from geographically close islands. These patterns appear to contradict similarities implied by previous subspecific designations based largely on color and pattern differences. Genetic drift, gene flow, and selection are evaluated as explanations for observed phenetic patterns. Drift appears to be highly unlikely as a major force determining regional, large island, and small island similarities among OTUs. Channel depths and estimates of the rate of net increase in sea level suggest that the northern islands are younger than the southern islands, supporting the idea that gene flow has been restricted among the southern islands and between the two regions for a longer time than among the northern islands. Combined with differences in selection regimes, the recency of gene flow appears to have been important in determining north-south phenetic similarities. Populations on small islands are exposed to qualitatively different selection regimes than those on large islands. The closer similarity of northern, small island OTUs to large island OTUs suggests that the northern OTUs have not responded to small island selection regimes to the same extent that southern island OTUs have. [Phenetics; Podarcis sicula; P. melisellensis; Yugoslavia; Adriatic Sea, island populations.] The taxonomic and ecological diversity of the lacertid lizards of the Mediterranean region make them favorable subjects for a variety of evolutionary studies. A number of studies have been reported, but the majority have concentrated on the taxonomy of geographic isolates. Of the 13 species of Podarcis (formerly in the genus Lacerta; Arnold, 1973) occurring in the region, more than 172 subspecies have been described, most of these being populations restricted to single islands (Mertens and Wermuth, 1960; Brelih, 1961; Lanza et al., 1971; Lanza and Capolongo, 1972). The extensive works on subspecific nomenclature have emphasized differences among populations showing geographic variation, but unfortunately may also have obscured patterns of similarity for which general explanations may exist (Wilson and Brown, 1953). Population biologists are especially interested in attempting to discover the underlying cause and effect networks responsible for widespread patterns of similarity since such patterns should be the result of the dynamic interactions of widespread ecological and evolutionary forces (Ehrlich and Holm, 1962). The nature and extent of phenetic variation among local populations can generally be attributed to gene flow, genetic drift, and natural selection, yet it is difficult to distinguish the relative importance of these forces in determining patterns of geographic variation in natural populations (Gould and Johnston, 1972). This may be possible by examination of phenetic relationships among insular populations of lizards, however, since rates of gene flow are extremely low, environmental heterogeneity varies as a