Conditions for Protected Polymorphisms in Subdivided Plant Populations. 2. Seed Versus Pollen Migration

Abstract

The effect of sexually variable migration and selection are explored within the general context of Wright''s island model of migration. An analysis for the development of protection of polymorphisms is constructed for a migratory system in which pollination is strictly localized within mating-selection demes, but fertilized seed from each deme create a zygotic pool for regenerating all demes. Selective differences in pollen and ovule production affect the maintenance of polymorphisms in different ways and a mixture of homozygote excesses and deficiencies can exist for different alleles at a multi-allelic locus. A system of sedentary pollen with migrating seed is contrasted with a system of migrating pollen with sedentary seed distribution. This latter system is strongly protective of polymorphisms and always creates a deficiency of homozygotes below Hardy-Weinberg expectations even in the absence of selective differences. The effect of the sexes on evolutionary dynamics is not just a matter of reversing sex roles since gamete versus zygote dispersal requires different supporting effects from the migrating and sedentary sexes. These 2 systems are compared with systems of pollen and seed migration and with pollen and seed localization with respect to the protection afforded polymorphisms and departures of homozygote frequencies from Hardy-Weinberg expectations. The effects of environmental heterogeneity on all systems are also compared. Relationships of these models to other models are drawn.