PARENT SESSION
Oral Session # 54: Coastal Ecosystems: Salt Marshes.
Presiding: P Ringold
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 105.
Genetic diversity and fine scale population structure of the salt marsh perennial Borrichia frutescens.
Richards, Christina1, Donovan, Lisa1, Hamrick, James1, 1 University of Georgia, Athensa, GA, USA
ABSTRACT- We used enzyme electrophoresis to evaluate fine-scale population genetic structure of Borrichia frutescens L., a coastal salt marsh perennial in the southeastern U.S. We hypothesized that the extreme environmental gradients in this habitat would lead to high genetic structure compared to other outcrossing perennial species and to genetic differences among plants in different microhabitats along the gradients. We also hypothesized that at very fine spatial scales, extensive ramet production would cause subpopulations to be dominated by a few large clones. To test these hypotheses, we sampled individuals from populations representing the full distribution of this species in the marshes of Sapelo Island, GA. At 5 sites, leaf tissue was collected from 96 individuals at 1 m intervals on grids spanning the environmental and height gradients. Fifty-eight percent of the 17 loci examined were polymorphic, with 41.2% polymorphic within populations. Our estimate of genetic structure for Borrichia (GST = 0.139) was slightly higher than other outcrossing, long-lived perennial species (GST = 0.094, Hamrick and Godt 1996), indicating only moderate barriers to gene flow. There was no evidence of genetic differentiation among microhabitats within populations. Within populations, average GST among microhabitats was 0.042. Across populations, genetic diversity (He) was equivalent for the three microhabitats (average He = 0.089). Clonal diversity varied but populations often contained many multilocus genotypes, indicating that both sexual reproduction and recruitment from seeds are important factors maintaining diversity. In conclusion, barriers to gene flow appear to maintain slightly more differences among populations than would be expected for an outcrossing perennial species. However, the environmental gradient does not seem to have a strong influence on the fine-scale distribution of genetic diversity at these loci.
Key words: microscale differentiation, clonal plant, population genetics, allozymes