Mating system and genetic variability in the simultaneously hermaphroditic terrestrial gastropod Balea perversa on the Baltic island of Oland, Sweden

Abstract

Random amplified polymorphic DNA (RAPD) technique was used to analyse the mating system of the simultaneously hermaphroditic land snail Balea perversa and to examine the level of genetic variability in eight natural populations of this rock-dwelling gastropod on the Baltic island of Oland, Sweden. The mode of reproduction was assessed in parent-offspring comparisons, in which parents (virgin at the beginning of the breeding experiment or wild-caught individuals with prior reproductive experience) were kept either singly or in pairs. Snails with no prior reproductive experience produced 1-10 offspring exclusively by selfing, no matter whether they were kept singly or in pairs. In contrast, low rates of outcrossing occurred in snails with prior reproductive experience. Minimum estimates of outcrossing were 10% for snails kept singly and 16% for snails kept in pairs. Corresponding maximum likelihood estimates of outcrossing ranged from 16 to 25%. The results indicated that sperm stored from previous matings were used for cross-fertilization. At the population level, AMOVA analysis showed that most of the genetic variability (84%,) occurred among populations of B. perversa and only 16% within populations. In two populations genetic variability was completely absent in the DNA fragment patterns examined. This finding agrees with the mode of reproduction in B. perversa. Frequent selfing may account for the low within-population variability compared with the moderate among-population variability in this species.