Getting used to heat stress helps against heavy metals

The world holds many forms of stress for animals. Take our freshwater, for example. This is increasingly under pressure from a wide range of man-made stresses, such as climate change and various forms of pollution. How can animals adapt adequately to everything? With a rapidly changing climate, it is crucial to understand the impact this has on other challenges, and vice versa.

Stress + stress = ?

"Some organisms have a remarkable ability to quickly adapt genetically to changing living conditions. This can have surprising consequences," says NIOO's aquatic ecologist Steven Declerck. He led the research done by NIOO, Wageningen University and KU Leuven. "For example, a better ability to cope with one type of stress can influence how sensitive organisms become to other stress factors. Adaptation can lead in some cases to increased resilience to other stresses, but in other cases to heightened sensitivity."

Copper cost

It is a tiny animal less than a millimetre in size that lives in freshwater: the rotifer. Yet it plays a leading role in research. In an evolutionary experiment, populations of rotifers lived for several months with either increasing heat or copper amounts. Heat waves are becoming more common due to climate change, and copper can be toxic to freshwater life. Declerck: "Although copper pollution has been reduced in Europe in recent decades, it is still a real threat in many other places around the world." Through industrial and domestic wastewater, mining and pesticides, it ends up in nature.

Experimental evolution

Monitoring stress-driven evolution in the lab in real time, that's what the researchers did. And what are the ecological consequences? The study started with populations that each consisted of 50 different clones of rotifers. Those clones started reproducing sexually with each other and the populations were found to genetically adapt to stress within a short time. At the end, the populations were presented with all situations in a so-called common garden experiment. Declerck: "Surprisingly, this showed that populations that adapted to heat became insensitive to copper poisoning, while adaptation to copper did not involve increased tolerance to heat."

Common phenomenon

What can we do with the conclusions? "Our research shows that periods of high temperatures can make populations more resilient to local pollution," explains Declerck. This is good news. That probably has to do with breeding general ways of coping with stress. But rotifers that adapt to pollution do not appear to be more resistant to heat, unfortunately. That requires more specialised 'detoxification traits' that provide limited rather than broad protection against stress. "It is important for environmental management and conservation to now further investigate how common this phenomenon is. That means: looking at other combinations of types of stress and organisms."

More information

• Article in Global Change Biology: Asymmetric micro-evolutionary responses in a warming world: heat-driven adaptation enhances metal tolerance in a planktonic rotifer, but not vice versa.

Text: NIOO-KNAW
Images: Suzanne Wiezer, NIOO-KNAW; Steven Declerck, NIOO-KNAW