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Run-off from Road Salts Leads to Rapid Evolution in Freshwater Zooplankton

Joanna Lawrence
7th January, 2017

A team of researchers has found that freshwater zooplankton can evolve rapidly to tolerate deicing road salts. Daphnia plankton can develop a genetic tolerance to high salinity levels within two and a half months. This is potentially good news for freshwater ecosystems, which are currently experiencing sudden changes in salt concentrations as the use of road salts increases. The details are in a paper that was just published in the journal Environmental Pollution. The use of sodium chloride as a road deicer has led to salinity changes in local ecosystems. Freshwater systems such as lakes and rivers can be heavily impacted by salt run-off. Researchers have already found evidence of harm—road salt can alter frog sex ratios, change food webs, and stress out fish. Few studies had focused on individual species, however, and how they might adapt over time. Scientists funded by the Jefferson Project at Lake George studied the effects of high salinity on Daphnia pulex, a common species of freshwater zooplankton. Daphnia, also known as water fleas, are an important source of food in many freshwater ecosystems. The team exposed the plankton to different salt concentrations to see how they fared over time. After two and a half months, the plankton were moved to aquariums with low salinity. They were allowed to breed for three generations and their offspring were tested for salt tolerance. The researchers found that the offspring of plankton that had been exposed to high salt concentrations were more tolerant of salt. In other words, the plankton had developed a genetic tolerance and passed it on to their offspring. This happened in only two and a half months—an example of rapid evolution. The findings show that some animals may evolve quickly to adapt to changing environments. Daphnia, common zooplankton, evolved a resistance to high salinity in less than three months. While this may sound positive for freshwater ecosystems, the authors caution that road salt may still be harmful to other animals. Furthermore, the plankton were not able to adapt to the highest salinity levels tested by the researchers—showing that there is a limit to their adaptability even when evolution is rapid. REFERENCE Coldsnow et al. Rapid evolution of tolerance to road salt in zooplankton. Environmental Pollution (2017).