Genetic rescue versus outbreeding depression in Vallisneria americana: Implications for mixing seed sources for restoration

The selection of seed stock for restoration remains a complex issue. Using local stock reduces the chances of outbreeding depression or genetic dilution, whereas mixing sources may increase diversity and counteract inbreeding depression. Evaluation of these opposing approaches remains difficult when planning a restoration project but is needed to increase chances of long-term population persistence. We evaluated seed production and germination success of seeds from controlled reproductive crosses of the submersed aquatic plant Vallisneria americana (wild celery) collected from populations throughout the Chesapeake Bay. We assessed differences in seeds, capsules, and germination success in three types of crosses: (1) individuals within-populations, (2) among-populations but within-genetically differentiated regions, and (3) among-regions. We observed population level differences in within-population and among-region crosses. Levels of genetic relatedness among individuals, genetic diversity within populations, or differentiation across populations did not predict reproductive success. Our data show that mixing sources from different populations and regions has both benefits and drawbacks. Thus, minimizing the risks of outbreeding and inbreeding depression, presented as a mostly dichotomous issue in the restoration literature, is not an either-or issue in V. americana.