Sperm utilization in subadult and adult simultaneous hermaphrodite snails mating in the wild

Abstract

In species with multiple mating and long-term sperm storage, males are expected to show a preference for mating with virgin and young females to reduce the risk of sperm competition. In various simultaneous hermaphrodite land snail species, sperm production precedes egg production by 2–4 weeks, resulting in a short period of protandric hermaphroditism before shell growth is completed. In a natural population, we collected copulating pairs of the simultaneous hermaphrodite land snail Arianta arbustorum (L., 1758) consisting either of two adults, of two subadults, or of one adult and one subadult snail, and determined the paternity of their hatchlings that emerged from subsequently deposited eggs. Adult snails used sperm received from subadult mating partners for egg fertilization in the same frequency as sperm from adults, indicating that subadult and adult snails do not differ in male function. Furthermore, an unfinished shell is not a reliable indicator for virginity, because 35% of the subadult individuals had already sperm stored from previous mating(s). Compared with adults, young individuals exhibited a lower risk of sperm competition, indicated by a higher last mate sperm precedence. However, subadult snails produced fewer eggs than adult snails, counteracting the evolutionary advantage of preferring a young partner with low sperm competition risk.