CS39A Zooplankton - Feeding, Reproduction, Growth and Molecular Diversity
Date: Tuesday, June 11, 2002
Time: 3:00:00 PM
Location: View Royal
 
CaceresCE, University of Illinois, Champaign, USA, caceres@life.uiuc.edu
Tessier, A, J, Kellogg Biological Station, Hickory Corners, USA, Tessier@kbs.msu.edu
 
WHAT DETERMINES THE HATCHING FRACTION OF DIAPAUSING EGGS IN LAKE DAPHNIA POPULATIONS?
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Although it is widely recognized that diapausing eggs accumulate in the sediments of many lakes, the links between the active and dormant stages are still poorly understood. Theory predicts that the fraction of eggs that terminate dormancy within the first year should be related to variation in annual habitat quality. Earlier results had indicated that the hatching fraction varied considerably between a population that was able to persist year-round in the plankton versus one that was eliminated annually. Over 60% of newly produced eggs hatched in the annual population whereas only 9% hatched in the perennial population. To determine the relative importance of source population vs. environmental effects on the hatching fraction in Daphnia pulicaria, we conducted a series of reciprocal transplant experiments with newly produced diapausing eggs from five populations. After being incubated at the bottom of the lakes for one year, average hatching fraction ranged from 6% to 50% across the five populations. Our results suggest that the hatching fraction was primarily determined by lake-specific environmental cues, suggesting environmental constraint on the use of the egg bank.