HIERARCHICAL GENETIC-STRUCTURE AND GENE FLOW IN MACROGEOGRAPHIC POPULATIONS OF THE EASTERN TENT CATERPILLAR (MALACOSOMA-AMERICANUM)

Genetic structure and inferred rates of gene flow in macrogeographic p opulations of the eastern tent caterpillar Malacosoma americanum were analyzed at two hierarchical scales: local demes and regional subpopul ations. Wright's F-statistics were used to estimate population genetic structure using multilocus genotypic data generated electrophoretical ly. Estimated values of F-ST and the distribution of private alleles w ere then used to obtain indirect estimates of gene flow. We found mode st, though significant, genetic structure at both spatial scales, a pa ttern consistent with high rates of gene flow over the large distances involved. Modest values obtained for Nei's genetic distance also sugg ested high levels of gene flow across the range of this species, altho ugh some gene-how restriction resulting from isolation by distance was suggested by a positive regression of genetic distance on geographic distance. The observed homogeneity at enzyme loci across the range of M. americanum parallels the reported uniformity in morphology, suggest ing a general absence of local genetic differentiation in this widely distributed species. The genetic homogeneity observed in this wide-ran ging insect is discussed in terms of organism-specific environmental e xperience at different spatial scales. Some organisms occupying appare ntly heterogeneous environments may ameliorate unsuitable local condit ions through microhabitat selection or behavioral modification of thei r microenvironment. This may be accomplished in M. americanum through group shelter construction and behavioral thermoregulation, closely ty ing thermoregulation to social biology in this species. If in this way the tent helps produce an effectively homogeneous environment for thi s species across its extensive range, this system may provide a unique example of how social behavior can influence the distribution of gene tic variation in a population.