High levels of selfing are revealed by a parent-offspring analysis of the medically important freshwater snail, Bulinus forskalii (Gastropoda: Pulmonata)


The hermaphroditic freshwater snail Bulinus forskalii acts as intermediate host for the trematode Schistosoma guineensis, an agent of human intestinal schistosomiasis. Despite the medical importance of this snail, little is known about its mating system, even though this influences the epidemiology of schistosomiasis. Therefore, a parent-offspring analysis was carried out to elucidate its mating system. Eleven highly polymorphic microsatellites generated multilocus genotypes, enabling parentage assignment to all of the 432 offspring reared from 28 pairs of laboratory-bred B. forskalii. Ninety percent of progeny were of uniparental origin, and only six pairs (21% of parents) produced mixed clutches of crossed and selfed progeny. No pair reproduced exclusively by outcrossing. These results provide compelling evidence that B. forskalii has a mixed mating system dominated by uniparental reproduction, in agreement with indirect assessments from studies of population genetic structure and inbreeding effects. This reproductive strategy may be pivotal to the persistence of B. forskalii in its patchy, temporally unstable habitats, as well as helping it to cope with its parasitic burden.