Scientists at the Max Planck Institute of Limnology at Plön, Germany, have been successful in demonstrating how populations of small planktonic crustaceans (Daphnia) adapt to changing environmental stress by shifts in the frequencies of resistant genotypes. Nelson G. Hairston jr., guest researcher from Cornell University, NY, and Winfried Lampert, director at the Max Planck Institute of Limnology (MPIL), and colleagues report in the issue of 30 September 1999 of Nature that during the course of eutrophication of Lake Constance, the genetic composition of the Daphnia population shifted towards genotypes, which were less sensitive to toxic cyanobacteria (blue-green algae). Daphnids play an important role in the ecosystem as they clear the water by filtering out algae and are also a major component of fish food.
The occurrence of cyanobacteria, some of them being toxic, is a nuisance when lakes are enriched with nutrients (eutrophication). The first symptoms of eutrophication of Lake Constance from nutrient input through waste water were detected in the 1960s. The peak of the eutrophication with algal blooms was reached around 1980 before the lake responded to extensive efforts to reduce nutrient input, which resulted in the presently high standard of water quality. Although the large Lake Constance never had massive cyanobacteria blooms like other eutrophic lakes, blue-greens were present at measurable quantities. Even low proportions of toxic cyanobacteria in their food algae inhibit growth and reproduction of Daphnia or may even kill them. However, research at the MPIL showed that these animals are not helpless, but can adapt to the changing food resources.
Although such genetic shifts have been demonstrated in the laboratory, it is
hard to demonstrate their relevance under field conditions. as genotypes that
lived before the environmental change occurred cannot be studied physiologically
in retrospect. The scientists at the MPIL used a trick to cir
Contact: Wilfried Lampert