Genetic drift in small and recently founded populations of the marine snail littorma saxatilis

Abstract

The intertidal snail, L. saxatilis lacks a pelagic stage and migration between populations inhabiting different islands is rare. Small skerries, which are very young habitats, due to the proceeding post-glacial elevation of land, are likely to have been populated by small groups of snails. Mayr’s “founder principle” predicts a “genetic revolution” in populations established in this way. Allozyme data, however, reveal but a slight decrease in the level of heterozygosity within these skerry populations, as compared to those of islands and mainland. A probable explanation for this is that although the founding group may consist of only one fertilised female, sperm storage, year-round reproduction, and density-dependent selection enable such populations to expand rapidly in a formerly empty habitat. As has been shown by Nei and coworkers, this will largely impede the loss of genetic variation during the founder event. Isolated populations of L. saxatilis indicate that founder events need not lead to drastic genetic alterations. © 1987 The Genetical Society of Great Britain.