Linking genotypic diversity and reproductive success of Vallisneria americana from the Chesapeake Bay to enhance current and future restoration strategies

Background/Question/Methods

The controversial issues that arise when planning and implementing restoration initiatives, even at local scales, are growing more complex as ecologists begin to consider restoration in the face of climate change. Currently, two contradictory paradigms for selecting restoration source material call for either maintaining the purity of local genetic stock to reduce chances of genetic dilution by maladapted genes and outbreeding depression or mixing disparate sources of stock to increase diversity and counteract inbreeding depression. Meanwhile, managed relocation (MR) is an emerging restoration strategy to address biodiversity management across broad scales when both persistence and recolonization are not possible due to the effects of climate change. Advocates of MR claim that climate constrains the distribution of most taxa and that rapid habitat shifts associated with future climate change will limit dispersal capabilities and thus warrant the intentional movement of populations to locations where their probability of future persistence is predicted to be higher. Understanding the scales at which the risks of inbreeding or outbreeding are most prevalent is lacking for most populations, yet this information is critical for both current and future restoration effectiveness. We assessed the risks and benefits of either maintaining local restoration stock or mixing desperate sources by evaluating seed production and germination success of seeds produced from controlled reproductive crosses of the submersed aquatic plant Vallisneria americana(wild celery) collected from populations throughout the Chesapeake Bay.

Results/Conclusions

Specifically, we analyzed differences in seed traits, capsule traits, and germination success in crosses from individuals within-populations, among-populations but within-genetically differentiated regions, and among-regions of the Chesapeake Bay. We found significant differences in seed and capsule production within-populations as well as in some among-region crosses. Among-population crosses within genetically defined regions were not different from within-population crosses. However, differences in seed production in crosses occurring among-populations and among-genetic regions depended on the individual populations included in the cross. We found that our ability to predict either an increase or decrease in seed production or germination based on genetic relatedness among individuals, genetic diversity within populations, or differentiation across populations was poor. The use of these genetic metrics for assessing risk of outbreeding depression balanced by genetic rescue is more limited than previously described. Expanding this research beyond the local scale of the Chesapeake Bay we examined how genetic diversity of V. americana is structured in freshwater-tidal rivers across the latitudinal gradient of the eastern United States.