KU Leuven Finds Metal Pollution Counteracts Evolutionary Benefits in Warming Waters
The research focused on the water flea (Daphnia magna), a crucial player in freshwater ecosystems. The water flea is an algae eater and helps keep water clear in shallow lakes. Dormant eggs of this water flea can survive in sediment layers for decades and ‘rise’ again under the right conditions.
By comparing two subpopulations of water flea from the same lake, 40 years apart, the study confirms that these organisms have rapidly adapted to an increase in the number of heat waves over that time period, and are better able to withstand increasing heat stress.
This rapid evolution sounds like good news. But this study also investigated what happens when the organisms are exposed to pollution, specifically zinc.
The improved heat tolerance in the recent subpopulation was significantly reduced. Even to the extent that the evolutionary advantage of a better heat resistance was completely lost due to the damaging effects of pollution.
Researcher Ying Dong: “We raised Daphnia magna water fleas from sediment layers from different time periods (1955-1965 and 1995-2005) and exposed them to different conditions of heat and zinc contamination. The results were clear: while the more recent subpopulation showed improved heat tolerance, this advantage was completely negated when zinc was introduced, resulting in a similar vulnerability to heat compared to the older subpopulation.”
“We observed a greater decrease in energy reserves with zinc exposure in the more recent subpopulation. This was also associated with more oxidative damage. This suggests a lower defense against oxidative damage. It is assumed that the pollutants reduce heat tolerance because more energy is needed to recover from the pollution.”
Professor Robby Stoks, research group Evolutionary Stress Ecology and Ecotoxicology
The findings support a key evolutionary trade-off. The ability to better tolerate heat confers increased sensitivity to pollutants. This interplay between multiple stressors is likely common because coping with stressors is increasingly energetically costly. This underscores the complexity of ecological responses in an era of rapidly changing climate and environmental conditions.
“Our results show that while some species can adapt rapidly to rising temperatures, the presence of pollutants can completely undermine these adaptations. This interaction between warming and pollution must therefore be taken into account in climate strategies and ecological risk assessments,” concludes Professor Stoks.