Ecological genetics of a marine copepod inhabiting clean and contaminated intertidal mudflats

Each year up to 20% of pesticides can be transported into the estuaries (through aerial and runoff losses), which are sensitive nurseries of commercially and ecologically important species. Toxicants can exert rapid, strong selective pressures on populations than can ultimately lead to broad genetic changes and provide unique opportunities to study the processes of natural selection and evolution by exploiting environmental toxicants as controlled stressors in experiments.; The effects of contaminants in the genetic population structure of the ubiquitous harpacticoid copepod Microarthridion littorale (Poppe 1881) were examined. Central to the successful completion of this project was the development of a DNA isolation procedure that provided template of sufficient quality and quantity to consistently amplify DNA from single specimens (Chapter 1).; Relationships among populations (southeast Atlantic and northern Gulf coast, USA) of M. littorale were estimated using sequence data from two loci: cyt b and ITS-1 (Chapter 2). Phylogenetic trees based on both genes were generally concordant, and suggested that M. littorale populations are structured over large geographic scales (hundreds of km). Three well-supported groups were found in both gene trees comprising clades of alleles sampled from South Carolina, Florida, and Louisiana.; In Chapter 3, analysis of the resulting cyt b diversity within and between populations of the M. littorale from 10 estuarine creeks, mainly in South Carolina, revealed the presence of three distinct mitochondrial lineages. The distribution of the three M. littorale mitochondrial groups had no geographic pattern but were weakly correlated with degree of contamination of each creek.; The three mitochondrial lineages were subjected to high concentrations of a mixture of two pesticides, chlorpyrifos and DDT, to compare survival rates (Chapter 4). The most frequently encountered mitochondrial group in the field, survived better in the presence of pesticides relative to the others. The other two types were significantly reduced in the presence of pesticides compared to the robust type. The experimental data corroborate the distribution patterns of the three mitochondrial groups sampled from clean and contaminated tidal creeks on the South Carolina coast and suggest that contamination play an important role on structuring the genetic composition of M. littorale .