David J. Berg1, James A. Stoeckel2, Todd D. Levine2, and K. Douglas Blodgett3.
Department of Zoology, Miami University, 1Hamilton, OH 45011 or 2Oxford, OH 45056; 3The Nature Conservancy, Illinois River Project Office at Emiquon, Lewiston, IL 61542
North American freshwater mussels are continuing to suffer dramatic declines in population size due to a number of anthropogenic stressors such as habitat destruction and commercial harvest. Within populations, neutral genetic variation is lost because of genetic drift. The intensity of drift is negatively correlated with population size. In turn, population size is dependent on demographic parameters such as mortality, migration, and recruitment rates. Thus, demographic and genetic features of populations should be tightly linked. We are developing a stage-based model to investigate the effects of variation in mortality on population size and genetic diversity. Demographic parameters for this model are derived from published data for species of mussels that exhibit considerable variation in population ecology, while our own research has provided measures of population genetic variation using a variety of molecular markers (allozymes, mtDNA sequences, microsatellites) for many species of mussels across a large portion of North America. Using STELLAš software, our model incorporates a variety of demographic parameters (age-structure, age-specific mortality, recruitment) and population genetic parameters (haplotype frequency, heterozygosity). We will use this model to examine effects of constant and age-specific mortality on populations that have varying levels of genetic diversity. Results of this model will provide insight into interactions of demography and population genetics. For example, we should be able to compare changes in population size and genetic diversity under contrasting scenarios of age-specific mortality due to harvest regulations and constant mortality due to habitat degradation. We will also examine the importance of migration by comparing isolated populations to populations within a tightly linked metapopulation. While changes in population demography are important for estimating extinction risk for populations in the short-term, survival over evolutionary time is dependent on maintenance of genetic variation. Models that incorporate both demographic and genetic features of populations should be of great utility for the development of effective conservation strategies.