Temporal Changes in a Natural Population of Copepods

¹ Department of Biological Sciences, University of Maryland Baltimore County, Catonsville, Maryland 21228

Adaptation was measured in a natural population of the estuarine copepod, Eurytemora affinis (Poppe). Significant changes occurred between generations in tolerance to elevated temperature and in body size, in both sexes, and in reproductive traits in females. If these changes were genetic, they did not result in different heritabilities for the traits and genetic variation was maintained in the population. However, genetic correlations between temperature tolerance and brood size in females showed significant changes between generations, lending support to two models for the maintenance of genetic variance. Linkage disequilibrium is discussed as an alternative explanation for the observed genetic changes that took place and for decreased hatchability of broods. Evidence for decreased hatchability, measured as proportion hatch, suggests summer diapause in this species.