High-speed evolution observed in daphnia

Daphnia, also known as water fleas, play an important role in the food web of lakes: they feed on phytoplankton and are eaten by predators such as fish. Their food resources show marked seasonal variation: in eutrophic waters, the summer is particularly challenging for daphnia, as the phytoplankton community is dominated by cyanobacteria (blue-green algae), which are of poor nutritional quality and often contain toxins. Adaptation on a short time scale. Certain daphnia genotypes are known to be resistant to dietary cyanobacteria. These would therefore be expected to reproduce more effectively in eutrophic lakes, and in an earlier study in Lake Constance natural selection of this kind was indeed observed over a period of several years. Researchers from Eawag and Cornell University now wished to investigate how rapidly this adaptation occurs. Their study, which began with the collection of samples from Oneida Lake in 2015, was recently completed while Cornell-based project leader Nelson Hairston Jr.