INTERSPECIFIC VARIATION IN THE ABUNDANCE, PRODUCTION, AND EMERGENCE OF<i>DAPHNIA</i>DIAPAUSING EGGS

Abstract

Despite the ubiquity of dormancy among invertebrates, the demographic ties between the active and dormant stages remain largely unexplored in most systems. Nevertheless, dormant stages could potentially have significant impacts on the ecology and evolution of the active population. In Oneida Lake, New York, populations of the suspension-feeding crustaceans Daphnia galeata mendotae and Daphnia pulicaria produce large numbers of long-lived diapausing eggs, which accumulate in the sediments to densities of over 2.5 × 104 eggs/m2 for D. galeata mendotae and 8.0 × 104 eggs/m2 for D. pulicaria. Sedimentation rates obtained by 210Pb dating suggest that these eggs can remain viable for >125 yr and that these two Daphnia populations have persisted in this system for >200 yr. Total annual production of new diapausing eggs can range from 0 to over 104 new eggs/m2 of sediment. Annual emergence rates back to the water column are also variable but only range between 0 and 25 Daphnia/m2. Because annual variation in the size of the overwintering water-column population ranges between 0 and 2.5 individuals/L, the contribution of emergence to the development of the spring population is considerable in some years and negligible in others. Despite similar maximum water-column densities, D. pulicaria produces and stores more eggs and has a higher rate of emergence than D. galeata mendotae, suggesting differences in the benthic–pelagic link of these two species. Diapausing eggs greatly increase the generation time of the populations that produce them and therefore have the potential to substantially alter the outcome of community interactions.