Morphological variations in populations of Lacerta from islands in the Adriatic Sea Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/ms35tc78h

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  • Phenetic relationships in insular populations of Lacerta sicula and L. melisellensis correspond to geologic ages of the islands in two regions of the Adriatic Sea. Populations of L. melisellensis on older islands are more similar to populations of L. sicula than are L. melisellensis from younger islands, and examination of characters reflecting trophic structures of these lizards suggests that convergent evolution has progressed further in the populations on older islands. A rough correspondence between phenetic similarities of populations and island sizes was investigated by means of multiple regression analyses in which geographic features of islands were used as independent variables and means of selected morphologic characters were dependent variables. Island area, length and distance to the mainland were the most important variables "explaining" interpopulation variations in measures of trophic structures, dorsal scale counts, and numbers of femoral pores in L. melisellensis. Lizards from small isolated islands generally have larger bodies, relatively wider snouts and heads, relatively longer heads, more dorsal scales, and more femoral pores than L. melisellensis from larger islands near the mainland. Larger lizards with relatively larger head dimensions on small islands are believed to be the results of adaptations to situations of reduced interspecific interactions and restricted distributions of food resources. Dorsal scale count variations may be related to climatic heterogeneity, but the evidence is inconclusive. Likewise, variations in the number of femoral pores may be related to variations in a balance between conflicting selective pressures for avoiding predation and facilitating intraspecific communication, but basic information on the functional significance of these characters is lacking. Measures of relative variation for ten meristic characters in L. melisellensis showed no significant pattern of variation, but levels of intrapopulation variation in ratios of head measurements to snoutvent lengths were generally lower in populations on small islands and higher in large island populations. Island area, length, the distance to potential sources of colonists and elevation were shown to be important variables in "explaining" geographic variations in levels of intrapopulation variability of trophic characters. Low levels of relative variation for trophic characters in populations from small isolated islands are generally associated with relatively high levels of sexual dimorphism in head width, suggesting that strong directional selection resulting from intraspecific competition for food has depleted genetic variation affecting these characters. Evidence from gene frequency data and body size distributions on small islands shows that genetic drift and founder effects complicate selectionist interpretations of these trends. The similarity of the trends identified in insular populations of Lacerta to trends identified in other insular populations of lizards suggests a generalized response of lizards to isolation.
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