Evolution cannot keep up with the pace of global warming, according to a study from the Norwegian University of Science and Technology. After spending four years investigating how zebrafish adapt to warmer conditions, the researchers determined that evolution will not be swift enough to save some species from the impacts of rising temperatures.
“It looks like evolution is slower than global warming in this case,” said study senior author Professor Fredrik Jutfelt. “This is the largest artificial evolution experiment that has been performed on vertebrates with a focus on heat tolerance.”
For the investigation, wild-caught zebrafish were bred based on their ability to cope with the most extreme conditions. Ultimately, the researchers followed about 20,000 individuals over six generations.
“We see that zebrafish can develop heat tolerance, and we have developed lines of zebrafish that can better withstand the heat. That’s good news,” said Professor Jutfelt.
“The problem is that evolution takes many generations. Evolution only increased the heat tolerance in the fish by 0.04 degrees C per generation. This is slower than the warming experienced by many fish in many places.”
Study lead author Rachel Morgan said that with the globe warming so fast, the fish may not be able to adapt to the warmest periods efficiently enough.
Evolution occurs when the best adapted individuals of a species produce more fertile offspring than the rest of the group. Over several generations, the adaptations accumulate and modify the species itself.
However, extreme heat can compromise the ability of fish to reproduce. Above a certain temperature, most of the fish die.
“How organisms adapt to these new conditions depends on their ability to withstand heat, to acclimatize, and the ability to pass on beneficial characteristics to the next generation,” said Professor Jutfelt.
Prior to artificial selection, one group of zebrafish was exposed to two weeks in warmer water. The researchers wondered if evolution would increase their capacity to acclimatize, but they found that this was not the case.
“Instead, the greater the ability of the fish to cope with the worst warm periods, the more their ability to acclimate decreased. So the gain in the form of higher heat tolerance was partly offset by a lower ability to acclimate. All in all, the rate of evolution was probably faster under the conditions in our laboratory than in nature,” said Morgan.
“It’s unlikely that some zebrafish populations, and other tropical fish species, will be able to cope with the temperatures that the planet may experience by the end of this century,” said Professor Jutfelt. “Some species that already live at the limit of what they can tolerate may not be saved by evolution. That is surprising and sad, and it means it is important that we stop warming the planet.”
The study is published in the journal Proceedings of the National Academy of Sciences.