Variation in polyandry, reproductive output, and within-brood genetic diversity in a marine snail population across seasons and years

Abstract

The frequency of polyandry has important implications for effective population size, genetic variation, and reproductive output. Compared to terrestrial organisms with complex social behaviors, the patterns and consequences of polyandry in marine populations are relatively less clear. Here we quantified polyandry in the Florida crown conch Melongena corona in the field under natural settings. We assessed the extent to which additional mates increase genetic diversity within broods, how polyandry relates to female reproductive output, and how consistent patterns are across their 5 mo reproductive season in 2 separate years. We found large variation in polyandry (2 to 19 sires per brood) and reproductive output among females. However, the number of sires per brood was unrelated to reproductive output. The number of sires increased genetic diversity within broods regardless of year or time of season. The number of sires per brood and reproductive output did not vary over the season or among years. Overall, our results show natural variation in polyandry upon which selection could act, but increased polyandry did not lead to females producing more hatchlings, and neither polyandry nor reproductive output increased over time when females could accumulate and store sperm. Any benefits of polyandry in terms of genetic diversity are expected to occur after hatching, if at all, rather than inside the egg capsule. Variation in polyandry could arise because males control mating and polyandry is less costly for females than trying to prevent superfluous matings.