The Maintenance of Genetic Polymorphism in a Spatially Heterogeneous Environment: Variations on a Theme by Howard Levene

Abstract

Levene''s model of polymorphism in a patchy environment is generalized and extended to include different patch structures and inbreeding. Starting with heterosis in each patch, as the fitness of the heterozygote decreases we pass through regions of average heterosis providing stable polymorphism, then one satisfying Levene''s condition for polymorphism, then a region of alternative equilibria (one polymorphic, one monomorphic), and finally fixation of one allele. Variation in inbreeding, patch abundance, and patchiness can have similar effects. Any of these can result in a discontinuity in the population structure along a continuous cline in environment.