SELFING, SEXUAL POLYMORPHISM AND MICROSATELLITES IN THE HERMAPHRODITIC FRESH-WATER SNAIL BULINUS-TRUNCATUS

Studies on the evolution of self-fertilization and sexual polymorphism s (the co-occurrence of several sexual morphs in a species) have focus ed on plants. Aphally, a sexual polymorphism occurring in gastropods, offers the opportunity to extend study of these issues to animals. We present progeny-array analyses of the selfing rate and correlated mati ngs in the tropical freshwater snail Bulinus truncatus. This study is based on 447 offspring originating from 57 families and five natural p opulations. To overcome the lack of allozyme polymorphism, four polymo rphic microsatellite markers were used. Selfing rates higher than 78%, were detected in all populations, and no correlation with the aphally ratio (the proportion of individuals lacking the male copulatory orga n per population) was evident. Outcrossing was detected in 17 families only, and individual outcrossing rates were variable and did not depe nd on the sexual morph of the mother. These results illustrate the pow er of microsatellites for detailed genetic studies, indicate that high selfing rates may have a strong genetic basis, and unexpectedly sugge st that phally polymorphism may be neutral with respect to selfing.