Researchers at KU Leuven investigated how well water fleas And the laurel plant Magna They can tolerate heat much better than they did 40 years ago. Then they looked at the relationship with water fleas’ sensitivity to pollutants. They did this by “resurrecting” the animals from 40-year-old eggs and comparing their heat resistance to that of modern animals. They then studied the effects of zinc, a common metal that can be toxic when present in high concentrations in lakes and rivers. And guess what? Today’s water fleas can tolerate heat much better than water fleas 40 years ago. But when the fleas encountered zinc pollution, this evolutionary advantage disappeared completely. That’s bad news.
“We’ve seen that the potential of rapid genetic evolution to save species may be less promising than we initially thought,” explains researcher Robbie Stokes. “Rising temperatures are just one of many stressors that organisms have to adapt to. Other factors, such as pollution, also play a role. If organisms learn to cope better with one factor (such as heat), they may at the same time cope less well with others (such as pollution).
stress proteins
It’s not yet entirely clear how this evolutionary trade-off works, but Stokes suspects that the energy balance of organisms plays an important role: “We have reserve molecules of fat, protein and sugar.” These molecules can be converted into energy. Achieving better heat tolerance requires a large portion of that energy budget. To deal with heat, organisms produce heat shock proteins that help the body when it gets too hot. They ensure that important proteins in our cells don’t get damaged by the heat. If proteins are damaged, heat shock proteins can help repair them. This requires a lot of energy, and that energy can run out. That leaves less to deal with other stressors, like contaminated zinc.
“Being able to tolerate heat better is not free,” Stokes continues. “Animals only develop this tolerance when it is needed, which is the case at the moment.” Why do stressors cost so much energy? It comes down to two mechanisms: “First of all, you have to defend yourself against them.” And that defense can fail. If it does, you then have to recover from the damage. That also costs energy, which we all get from our limited energy supply. If an organism is better at coping with one stressor, there is less energy left to defend itself against another stressor. That makes them more sensitive to it.
The entire animal kingdom also produces stress proteins to better tolerate heat, including humans. And while more and more studies show that animals can adapt to high temperatures in this way, this research suggests that this hopeful process could be offset by pollution.
