MEPS 497:105-117 (2014)  -  DOI: https://doi.org/10.3354/meps10565

ABSTRACT: Fine-scale variation in both the number and relatedness of genetic individuals can influence a range of ecological and evolutionary processes. However, we often have little information from natural populations regarding the fine-scale distribution of genetic diversity. We quantified multiple metrics of genetic diversity in the widespread, dominant marsh plant Spartina alterniflora across 3 spatial scales in 16 natural marshes in the Florida Panhandle. We also examined correlations between genetic diversity and marsh plant species diversity, along with key environmental variables that may influence both. Most of the variance in S. alterniflora genetic structure was explained by variation within sampling areas across sites. S. alterniflora genetic diversity and marsh plant species diversity increased with spatial scale within sites. In addition, diversity was generally higher on mainland marsh sites compared to discrete marsh islands, consistent with theoretical predictions from island biogeography and population genetics. Multiple metrics of genetic diversity increased with island area and with distance to the mainland. Despite significant correlations between diversity and tidal height, sediment organic content, and sediment porewater salinity, site type (mainland or island) and spatial scale were the best predictors of S. alterniflora genetic and marsh plant species diversity. We show that natural populations of S. alterniflora exhibit significant fine-scale spatial genetic structure, and thus continued loss of habitat could lead to a substantial loss of genetic diversity.

KEY WORDS: Genetic diversity · Isolation-by-distance · Relatedness · Genetic structure · Salt marsh · Island biogeography