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Genetic Structure of Populations of the Brown Snail (Helix aspersa). I. Microgeographic Variation
Robert K. Selander and Donald W. Kaufman
Vol. 29, No. 3 (Sep., 1975), pp. 385-401
Published by: Society for the Study of Evolution
Stable URL: http://www.jstor.org/stable/2407252
Page Count: 17
You can always find the topics here!Topics: Snails, Gene frequency, Alleles, Genetics, Population structure, Statistical variance, Population genetics, Habitats, Population size, Population estimates
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Microgeographic population structure in the land snail Helix aspersa was analyzed by determining genotypes at five enzyme loci for 2,218 individuals from 43 estivating colonies on two adjacent 10-acre blocks in Bryan, Texas. An analysis of genotypic proportions yielded no evidence of inbreeding within colonies; but allele frequencies for colonies on the same block were heterogeneous, and there were major differences in mean allele frequencies between blocks. The mean standardized variance (FST) for colonies on a block was .03. Seven demes occupying areas of approximately 500 square meters were identified on each block; the harmonic mean size of the demes was 15 individuals. Deme size in Helix apparently is much smaller than in Cepaea. Variance in allele frequencies among small colonies exceeded that among large colonies, as expected if random genetic drift is a significant factor affecting population structure. An examination of gross features of the habitat types of the colonies yielded no evidence of associations with allele frequencies. Nonrandom features of intercolony variation on blocks could reflect either selection in a spatially heterogeneous environment or incidents of drift occurring in the demographic history of the populations. From the standpoint of genic variation, as indexed by electrophoretically demonstrable protein variation, colonies of Helix on a single block are as heterogeneous as regional populations of Drosophila pseudoobscura in the United States; and the degree of genic differentiation of Helix populations in California may be equivalent to that of the human species as a whole.
Evolution © 1975 Society for the Study of Evolution