POPULATION GENETIC-STRUCTURE AND MATING SYSTEM EVOLUTION IN FRESH-WATER PULMONATES

Freshwater gastropods (Basommatophora and Prosobranchia) harbor a vari ety of mating systems. In particular, apomictic parthenogenesis in pro sobranchs and self-fertilization in the hermaphrodite pulmonates may b e viable alternatives to outcrossing sexuality in a number of species. The coexistence of different mating systems in extant populations pro vides opportunities to examine the forces directing their evolution. W e review the models analyzing and predicting genetic variability in su bdivided populations, with an emphasis on the effects of inbreeding. P opulation genetic data on freshwater pulmonates are examined in the co ntext of selfing rates and the loss of variability under selfing. Furt hermore, the genetic and demographic Factors thought to influence mati ng system evolution are considered, and we highlight the different app roaches available to estimate mating system parameters, in particular the selfing rate. Recent population biological studies on polyploid sp ecies (Bulinus truncatus, Ancylus fluviatilis) indicate that selfing i s the predominant mating system. These studies have contributed to a d eeper understanding of conceptual issues in the evolution of selfing r ates. Throughout, we emphasize the need for further carefully designed studies.