Hairston, Jr., N. G. Cornell University, NGH1@Cornell.edu
Lampert, W. Max-Planck-Institute for Limnology, Lampert@mpil-ploen.mpg.de
Caceres, C. E. Illinois Natural History Survey, Caceres@mail.inhs.uiuc.edu
Weider, L. J. Max-Planck-Institute for Limnology, Wei@mpil-ploen.mpg.de
IS THERE EVOLUTION OF GRAZER TOLERANCE TO DIETARY CYANOBACTERIA DURING LAKE EUTROPHICATION?
Long-lived diapausing eggs of zooplankton provide an opportunity to investigate microevolutionary processes in changing environments. In lakes that become eutrophied, the phytoplankton assemblage typically becomes dominated cyanobacteria. As the availability of more edible algae declines, we expect natural selection for tolerance to cyanobacteria in the diet of grazing zooplankton. We are testing this hypothesis for Lake Constance where sewage enrichment during the 1970s and 1980s led to significant cyanobacterial blooms, followed by substantial clean up. Viable diapausing eggs of Daphnia galeata are found in Lake Constance sediments from throughout the past four decades. Clones derived from three periods (pre-, peak-, and post-eutrophication) are being reared in continuous flow-through chambers on 1 mg C per liter of either "good" food (pure Scenedsemus) or "poor" food (a mixture of Microsystis and Scenedesmus). The ratio of the juvenile growth rates, g, on these foods (i.e., g-poor/g-good) is a
measure of tolerance to cyanobacteria in the diet, and hence of fitness. Ratios close to 1.00 indicate high tolerance (low fitness reduction on poor food); low ratios indicate low tolerance. We will report the results of this study, which is in progress.
Day: Wednesday, Feb. 3
Time: 04:30 - 04:45pm
Location: Hilton of Santa Fe