Can species evolve fast enough to survive as the planet warms?

For the first time, we saw a species that was in decline due to extreme weather recovering through rapid evolution. Does this mean that species increasingly affected by soaring 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 had to adapt to survive and migrate with the changing climate.

But the key issue is time. So far, the most rapid climate change we know about was the Paleocene-Eocene temperature maximum, which occurred about 56 million years ago, when temperatures rose by 5°C to 8°C over a period of about 20,000 years. Temperatures could now rise by more than 4°C by the end of the century. Can evolution really make a difference in such a short period of time?

The answer to that is definitely yes, at least for organisms with short generations. The most recent evidence comes from a wild plant called scarlet monkey flower (Mimulus cardinalis), which managed to develop a way out of the megadrought that hit California between 2012 and 2015.

Daniel Anstett at Cornell University in New York State and his colleagues began studying monkeyflowers in 2010, each year assessing how the plants were doing at a number of locations throughout their range and taking samples for DNA sequencing.

Monkeyflowers are water-loving plants that live along streams, Anstett says, so they were 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 actually died out. However, many of those that survived appeared to develop tolerance to drought within just three years, with many mutations in parts of their genome related to climate adaptation – and it was these populations that recovered the fastest from 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 been shown in the wild.

“It’s very hard to show because you need three things,” he says: showing that a population is declining because of a threat, that it has genetically adapted in response, and that these 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 developing pesticide resistance, and sandpipers adapting to extreme levels of US river pollution. But biologists weren’t able to check all three boxes in those cases, Anstett says.

“That third paper to be able to show that the recovery is explained by rapid evolution, which has never been done before at the scale of a whole range of species,” he says.

Andrew Storfer at Washington State University, who studies Tasmanian devils, acknowledges this. “To be clear, we showed rapid evolution in Tasmanian devils,” says Storfer. “But with the evidence in hand, we can’t link it to a demographic recovery.”

All of which says the three-year drought is weather, not climate. “It would take a while to demonstrate adaptation to climate change,” says Storfer.

In other words, the fact that monkeyflowers were able to evolve to survive one 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 increasingly extreme weather. “Extremes in the future may exceed the drought we’ve seen,” says Anstett.

What’s more, when populations decline, they lose genetic diversity—the fuel for evolution. If populations are repeatedly hit hard over a short period of time, their ability to evolve diminishes each time.

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

Still, Anstett sees his findings as good news. “A lot of these current predictions of species decline don’t take evolution into account,” he says. “This is a story of hope.

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