Impacts of Propagation on Population Genetics of the Threeridge Mussel Amblema plicata (Say, 1817)

Freshwater mussels provide many ecosystem services, but over the past century, they have become among the most imperiled taxa in the world. Often, efforts to restore mussel populations have included the propagation and release of juveniles. We utilized microsatellites to compare the genetic diversity of propagated mussels to the source population from which the broodstock was derived. Three wild-fertilized female threeridge mussels (Amblema plicata) sourced from the Cedar River watershed in Minnesota were used as broodstock. We then genetically characterized a sample from the source population, a subsample of the juvenile cohort directly after transformation (Juv-0Y), and another subsample of the juvenile cohort after 1 yr of being raised in the hatchery (Juv-1Y). After correcting for sample sizes, the Juv-0Y sample set contained the greatest allelic richness, followed by the source sample set and then the Juv-1Y sample set. All three sample sets exhibited alleles that were not shared with other samples sets, henceforth referred to as "private alleles." Private alleles in Juv-0Y and Juv-1Y indicated the dams (mothers) were likely fertilized by males living upstream of the source population, outside of the sampling effort of this study. High levels of multiple paternity were observed in the juveniles from both subsamples. In total, 89 juveniles were estimated to have been sired by 58 males, increasing the amount of genetic variability in the population. Analyses indicated the Juv-1Y samples were produced nearly entirely from a single dam, indicating that differential mortality in the hatchery reduced the amount of genetic variability in the released population. The Juv-1Y sample was significantly differentiated from the source, suggesting the juvenile population did not fully represent the source population. This study highlights the importance of genetic monitoring of mussels in hatchery environments to maximize the genetic diversity of the propagules that are released.