9701524 COULL The ability to survive in a state of suspended animation is commonly called dormancy or diapause. The spores of fungi and bacteria, the seeds of higher plants, the larvae of certain insects, and the cysts of some crustaceans, notably the brine shrimp (Artemia), are among the better known examples of diapausing stages in organisms. Among crustaceans (crabs, lobsters, shrimp, and their kin) those inhabiting inland bodies of water, especially those that occasionally freeze or dry, are more likely to possess a diapausing stage than are species living in the ocean. Diapause occurs, as expected, in many species of miniature freshwater crustacea called harpacticoid copepods, but it also occurs, unexpectedly, in at least two marine species. Since the marine environment is not likely to freeze or dry, the benefits of diapause are unclear. Three possible explanations account for the presence of diapause in marine species: (1) diapause arose in marine harpacticoid copepods and was retained in their freshwater descendants; (2) diapause arose in freshwater harpacticoid copepods, and was retained in their marine descendants; (3) diapause arose independently in freshwater and marine lineages of harpacticoid copepods. In this research, Bruce Coull and doctoral candidate Regina Wetzer will use molecular and anatomical data to establish the phylogenetic relationships of marine and freshwater copepods belonging to families known to contain diapausing species. These "family trees" and comparative methods will allow Coull and Wetzer to ascertain the evolutionary history of diapause in closely related families of harpacticoid copepods, and, in particular, to find out which hypothesis best explains how diapause arose in marine qpecies. The work may help provide a more general explanation of how diapause can arise in environments that are OstableO, lacking fluctuations such as Ocold-hotO or Owet-dryO seasons.
