POPULATION GENETIC-STRUCTURE OF THE BUTTERFLY MELITAEA-DIDYMA (NYMPHALIDAE) ALONG A NORTHERN DISTRIBUTION RANGE BORDER

The population genetic structure of the butterfly Melitaea didyma was studied along the northern distribution range border in Central German y by means of allozyme electrophoresis. Individuals were sampled from a total of 21 habitat patches from four regions, and two provinces. Sa mpling was designed to estimate local vs. regional differentiation. Hi gh levels of variability were found, H-e = 0.14-0.21. The mean expecte d sample heterozygosity from one region, Mosel, was significantly lowe r than from the Hammelburg region, H-e = 0.17 and 0.19, respectively. Two hierarchical levels of genetic differentiation were found. Within regions individuals sampled from different patches behaved as belongin g to one population with high levels of gene flow (Hammelburg F-ST = 0 .015, Mosel F-ST = 0.044), though local isolation barriers did create a substructuring of these populations. The inbreeding coefficients, F- IS, were constant over all sample levels, suggesting a similar distrib ution of habitat patches within regions. Between regions gene flow was limited. An isolation by distance analysis indicated that the hierarc hical structure, at the provincial level, may be breaking down due to isolation of regional populations. A more general observation was that the sampling design may greatly have influenced the estimation of gen etic differentiation. Depending on which samples were included, overal l F-ST estimates ranged from 0.059-0.090.