Document: JEN-3-47-4

Age, size, and genetic structure of Chesapeake Bay eelgrass (Zostera marina L.) demes.

RHODE, J.M.* and J.E.DUFFY

College of William and Mary, Virginia Institute of Marine Science, Gloucester Point, Virginia 23062 USA ¹

Abstract:
Preliminary allozyme surveys of Chesapeake Bay (Virginia, USA) populations of the clonal marine angiosperm Zostera marina L. (eelgrass) revealed substantial amounts of geographically-partitioned genetic variation. The observed population structure could be the result of adaptation to different environments or of nonselective processes, including founder events and drift. Two important demographic factors that vary among eelgrass populations and could affect genetic structure are age and size. To determine the effects of age and size on genetic diversity and structure in Chesapeake Bay eelgrass, we did an allozyme survey of 100 randomly-selected individuals from four replicate demes of three types [old (>65 years) and large (>100 hectares); old and small (<10 ha); young (<10 years) and small]. Genetic diversity at each of ten allozyme loci tested was greater among populations than within populations (FST = 0.78), and little genetic sub-structuring was evident within demes. Populations were in Hardy-Weinberg equilibrium (p > 0.05). Old, large populations contained less genetic diversity than young, small populations. Data from our allozyme survey, combined with results of reciprocal transplant experiments, indicate that selective forces and local adaptation might contribute much to the genetic structure of eelgrass populations. Studies of genetic diversity within and among these demes will help identify other forces that structure populations of this ecologically important species, allowing evolutionary interpretations and predictions to be made and management strategies created.

Keywords: genetic diversity, genetic structure, population age, population size, allozyme

This abstract is being presented at: 2:30 PM in session:
Oral Session #65: Wetlands, Estuaries and Salt Marshes.