Self-fertilization and monogenic strains in natural populations of terrestrial slugs

Abstract

Electrophoretic studies of genetic variation in 14 spp. of terrestrial slugs of the families Arionidae, Philomycidae and Limacidae [including Arion fasciatus, A. circumscriptus, A. silvaticus, A. intermedius, A. hortensis, A. subfuscus, Limax maximus, Lehmannia valentiana, Deroceras reticulatum, D. laeve, Philomycus carolinianus and 3 unidentified Philomycus spp.] in the eastern USA indicate that self-fertilization, either facultative or obligatory, is the normal breeding system in 6 of the species [including A. fasciatus, A. circumscriptus, A. silvaticus, A. intermedius and A. subfuscus]. Of these 6 spp., 3 are single monogenic strains; 1 consists of 3 monogenic strains; 1 includes a highly heterozygous form and 2 monogenic strains; and 1 has a moderate amount of polymorphism but little heterozygosity and strong linkage disequilibrium. Eight species are outcrossers, being highly polymorphic and panmictic within local populations. Niche breadth, assessed in terms of extent of geographic distribution and variety of habitats occupied and measured on an experimental plot of woodland, is greater in some monogenic strains than in highly heterozygous, outcrossing species. Colonizing success apparently is independent of the amount of genetic variation carried by a species.