Can species evolve fast enough to survive as the planet heats up?

For the first time, we saw a species in decline due to extreme weather recover through rapid evolution. Does this mean that species that are increasingly impacted by rising temperatures and other harsh conditions can adapt as the planet warms?

It is clear that evolution has saved countless species from climate change in the past. Over the past half-billion years, Earth’s climate has gone from much warmer than it is now – with crocodiles in the Arctic – to much colder. Plants and animals have had to adapt to survive and migrate with climate change.

But the key question is time. Until now, the most rapid climate change we have experienced was the Paleocene-Eocene Thermal Maximum, which occurred around 56 million years ago, when temperatures increased by 5°C to 8°C over a period of around 20,000 years. However, temperatures could increase by more than 4°C by the end of the century. Can evolution really make a difference in such a short time?

The answer to this question is definitely yes, at least for organisms with short generations. The latest evidence comes from a wild plant called the scarlet monkey flower (Mimulus cardinalis), which managed to emerge from the mega-drought that hit California between 2012 and 2015.

Daniel Anstett of Cornell University in New York state and colleagues began studying monkeyflowers in 2010, annually assessing the plants’ behavior at a number of sites across their range and taking samples for DNA sequencing.

Monkey flowers are water-loving plants that live along waterways, Anstett explains, and so they have been hit hard by the drought. “If you put one in a pot and didn’t water it for a few days, it would just die,” he says.

Three local populations have in fact disappeared. But many of those that survived appear to have developed drought tolerance in just three years, with many mutations in parts of their genome linked to climate adaptations – and it was these populations that recovered most quickly after the drought.

This is what biologists call evolutionary rescue: a species surviving a threat through rapid evolution. This has been demonstrated in several labs, but Anstett says this is the first time it has happened in nature.

“It’s very difficult to demonstrate because you need three things,” he says: showing that a population is in decline because of a threat, that it has adapted genetically in response, and that those genetic changes have allowed it to recover.

There are many possible examples of evolutionary rescue, including Galapagos finches changing in response to drought, Tasmanian devils evolving in response to transmissible cancer, pests evolving resistance to pesticides, and killifish adapting to cope with extreme levels of pollution in American rivers. But biologists haven’t been able to check all three boxes in these cases, says Anstett.

“This third link, to be able to show that the recovery is explained by rapid evolution, this has never been done before on the scale of an entire range of the species,” he says.

Andrew Storfer of Washington State University, who studies Tasmanian devils, agrees. “To be clear, we demonstrated rapid evolution in Tasmanian devils,” says Storfer. “But with the evidence in hand, we cannot link this to population recovery. »

That said, a three-year drought is about weather, not climate. “Demonstrating adaptation to climate change would take time,” says Storfer.

In other words, the fact that flower monkeys were able to evolve to survive extreme drought does not necessarily mean that they will be able to evolve to cope with a century or more of rapidly rising temperatures and ever more extreme weather. “Extremes in the future could eclipse the drought we experienced,” Anstett says.

Additionally, when populations decline, they lose their genetic diversity – the fuel of evolution. If populations are hit hard several times over a short period of time, their capacity to evolve diminishes each time.

So, as global warming continues, the threats will become greater and greater, but the ability of species to evolve will diminish. And long-lived species with long generation times have very little capacity for rapid evolution to begin with.

Still, Anstett considers his findings good news. “A lot of these current predictions about species decline don’t take evolution into account,” he says. “It’s a story of hope.”