Multiple paternity promotes genetic diversity in captive breeding of a freshwater mussel

Captive breeding can be an important supplement to habitat restoration in the conservation of threatened species. Careful choice of breeding regimes and genetic monitoring are essential to maintain genetic integrity and genetic diversity of target populations. Many species of freshwater mussels are threatened globally, and captive breeding has been employed many places. The genetic consequences of those breeding programmes are however largely unknown, as are the mating patterns that determine offspring genetic diversity. We explored changes in genetic diversity from adult freshwater pearl mussels to offspring in two alternative breeding approaches. Genetic diversity was measured at 15 microsatellite markers and mating patterns were reconstructed by parentage analysis. In the first approach, fertilisation took place among broodstock mussels in captivity, while in the second approach, fertilisation took place in the wild. In the population fertilised in captivity, female contribution was extremely skewed. This resulted in substantial loss of genetic diversity, but many sires within female broods (multiple paternity) limited the loss of genetic diversity. Fertilisation in nature largely maintained genetic diversity in the offspring, compared to sampled adult mussels, despite a skewed female contribution. Genetic diversity was maintained because a high level of multiple paternity allowed the number of sires to largely exceed the number of dams. Our results show the potential of genetic monitoring to improve stocking of freshwater mussels. We show different success in maintaining genetic diversity between the two breeding approaches and emphasise that the choice of methods should consider conditions for fertilisation in nature and reproductive contribution of mussels in captivity. Keywords: Captive breeding, Effective population size, Freshwater mussels, Mating system, Unionida