The structure of population genetic diversity in Vallisneria americana in the Chesapeake Bay: implications for restoration

Abstract

Submersed aquatic macrophyte beds provide important ecosystem services, yet their distribution and extent has declined worldwide in aquatic ecosystems. Effective restoration of these habitats will require, among other factors, reintroduction of genetically diverse source material that can withstand short-and long-term environmental fluctuations in environmental conditions. We examined patterns of genetic diversity in Vallisneria americana because it is a cosmopolitan freshwater submersed aquatic macrophyte and is commonly used for restoring freshwater habitats. We sampled 26 naturally occurring populations of V. americana in the Chesapeake Bay estuary and its tributaries and found that the majority of populations have high genotypic diversity and are not highly inbred. Fourteen of the populations had high allelic and genotypic diversity and could serve as source sites for restoration material. However, substantial geographic structuring of genetic diversity suggests that caution should be used in moving propagules to locations distant from their source. In particular, we suggest that propagules at least be limited within four primary geographic areas that correspond to freshwater tidal and non-tidal, oligohaline, and seasonally mesohaline areas of the Chesapeake Bay.

Does genetic diversity of restored sites differ from natural sites? A comparison of Vallisneria americana (Hydrocharitaceae) populations within the Chesapeake Bay

“…Our results suggest that natural populations of V. americana in the Chesapeake Bay are genetically diverse (see also Lloyd et al 2011) and that restoration practices are generally successful in re-establishing populations that are as genetically diverse as natural populations, especially when calibrated for the number of individuals sampled. All basic measures of genetic diversity (i.e., number of alleles, heterozygosity, proportion of polymorphic loci, number of genets) within restored sites mirror the levels of genetic diversity contained within their natural paired sites.…”

“…An effort to avoid exchanging materials among regions should also be actively adopted to maintain similar patterns of allelic composition. We detected genetic isolation between the Northern and Central Bay, with the division line roughly between DC and FB (Lloyd et al 2011), suggesting that movement of genetic materials across large geographic distances is limited. The majority of restoration projects have already been using local plant tissue for restoration.…”

“…Although the number of restored populations showing significant heterozygote deficit may be relatively small, they represent a large proportion of populations when compared to a Bay-wide sample, where only three of 27 natural populations showed significant heterozygote deficit (Lloyd et al 2011). The deficits in the restored populations could be the result of true inbreeding or of mixing individuals from different gene pools during planting, in essence a restorationinduced Wahlund effect.…”

“…Polymerase chain reactions (PCR) were performed as in Burnett et al (2009), with the exception of the locus Vaam_AAG004, for which we added dimethyl sulfoxide and Q-Solution (QIAGEN) to reactions to optimize specificity. PCR products were separated, measured, and peaks analyzed using identical methods and quality control procedures, which included repeated analyses to ensure high reproducibility of PCR reactions, as detailed in Lloyd et al (2011). Our final dataset contained 0.5% missing data.…”

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

“…As a dioecious species, small populations have an elevated risk of lacking compatible mates and may suffer increased effects from mating among relatives. Genotypic diversity in 26 Chesapeake Bay populations varies greatly, ranging from 0 (populations consisting of one single clone) to 1 (populations made up of completely unique genotypes; Lloyd et al, 2011), a phenomenon also seen for other clonal aquatic species (Arnaud-Haond et al, 2010). This means that sites ranged from having no detectable sexual reproduction to no detectable asexual reproduction.…”