Weak preference for conspecific mates in the hybridizing snails Viviparus ater and V. contectus (Mollusca Prosobranchia)

Abstract

Vivivparus ater and V. contectus frequently mate with each other in nature. We investigated mate preferences between the two species experimentally. Males were presented to females of either species and vice versa. Males of both species actively searched for mates and preferably mated with conspecific females. Females appeared passive and accepted matings from males of either species. Twenty-six per cent of heterosexual copulations were interspecific, suggesting either that the preference for conspecific mates, or that the ability to discriminate between partners of different species, is weak in Viviparus. Male-male copulations occurred at a rate of 5.1%, but these copulations were of shorter duration suggesting that some discrimination against male partners occurred. V. contectus males had a higher mating propensity than V. ater males. In both species, the majority of first contacts was initiated by males. First contacts between conspecific individuals were more frequent than between species, suggesting that snails are already more attracted to conspecific individuals from a distance. The proportion of first contacts ending with a copulation was higher in conspecific pairs than in interspecific pairs. Thus choices are made before and after establishing contact with another individual.