Data from: Increase in multiple paternity across the reproductive lifespan in a sperm-storing, hermaphroditic freshwater snail

Polyandry is a common phenomenon and challenges the traditional view of
stronger sexual selection in males than in females. In simultaneous
hermaphrodites, the physical proximity of both sex functions was long
thought to preclude the operation of sexual selection. Laboratory studies
suggest that multiple mating and polyandry in hermaphrodites may actually
be common, but data from natural populations are sparse. We therefore
estimated the rate of multiple paternity and its seasonal variability in
the annual, sperm-storing, simultaneously hermaphroditic freshwater snail
Radix balthica for the entire duration of the reproductive lifespan. We
also tested whether multiple paternity was associated with clutch size or
embryonic development. To obtain these data, we measured and genotyped 60
field-collected egg clutches using nine highly polymorphic microsatellite
markers. Overall, 50% of the clutches had multiple fathers, and both the
frequency (20–93% of clutches) and magnitude of multiple paternity (mean
1.3–3.8 fathers per clutch) substantially increased over time, probably
because of extensive sperm storage. Most multiply sired clutches (83%) had
a dominant father, but neither clutch size nor the proportion of developed
embryos per clutch was associated with levels of multiple paternity. Both
the evident promiscuity and the frequent skew of paternity shares suggest
that sexual selection may be an important evolutionary force in the study
population.