Can animals evolve fast enough to keep up with climate change?
The world is always changing, leaving plants and animals everywhere to adapt to new habitats and living conditions. Evolution offers a pathway for life to adapt to these changes, but it takes time. So as human-caused climate change increases the rate at which the environment is changing, the big question is, can evolution keep up?
Fortunately, at least for some lucky species, the answer may be yes. “Many creatures have a surprising capacity to cope,” says Sarah Diamond, an evolutionary ecologist at Case Western Reserve University (CWRU) in Ohio.
The traditional conception of evolution presents it as a gradual process, slowly shaping organisms over hundreds or thousands of years. In some cases, however, species can adapt much more quickly.
Research conducted over the past couple of decades has shown that evolution can occur on timescales similar to those of climate change. By figuring out what factors set the speed of evolution, scientists are hoping to identify what conditions give animals the best chances of keeping pace with the rapidly changing world.
In a new comprehensive review, Diamond and her colleagues pull together existing research on how quickly species can evolve climate-relevant traits, such as the ability to withstand high temperatures, dry conditions, or ocean acidification. Their sweep of the literature reveals plenty of good news. One of the laboratory experiments they consider, for example, shows that a species of green algae, Chlorella vulgaris, can rapidly evolve to tolerate temperatures 3 oC higher than its usual optimum.
Andrew Whitehead, who studies evolution and genomics at the University of California, Davis, says the species with the best chances of navigating the changes to come are those with large and genetically diverse populations. “Genetic variation is fuel for evolutionary change, and some [species] have more of that fuel than others,” he says.
Big, diverse populations can harbor more of the traits that might help a species adapt to new conditions. That, along with blisteringly fast reproduction, is why bacteria can develop resistance to antibiotics so quickly.
Yet quick adaptation isn’t limited to microbes. In his own research, Whitehead has shown that Atlantic killifish, a small silvery fish found off eastern Canada and the United States, has adapted to live comfortably in estuaries plagued by heavy industrial pollution. They pulled off this feat by having plenty of genetic variability to work with, says Whitehead. Killifish have the highest known levels of genetic diversity of any vertebrate. Combine that with a huge population and short generations, and you get a species stuffed with genetic mutations. Some of these mutations are helpful and give at least some individuals what they need to survive.
And that right there is the trick. When it comes to fast-moving challenges like climate change, “species can’t wait for new mutations to arise,” says Whitehead. “They need to hold those cards in their hand now.” It’s a situation where more is more. A species is “more likely to hold lucky cards if they’re playing with a big deck,” he says.
Australian scientist says hybridisation is the key
Most species are holding fewer cards than the killifish. But there are things animals can do to stack their decks—and people can help. Luciano Beheregaray, a molecular ecologist at Flinders University in Australia, says the key is hybridization; by mating with closely related species, an animal’s offspring could pick up the traits they need.
That’s how several closely related species of rainbowfish have navigated changing conditions in the Australian rivers they inhabit. The rainbowfish that dwell at higher elevations are adapted to the colder temperatures found there. As temperatures rise, warm-adapted fish from lower down are beginning to colonize the higher reaches of the rivers, often mating with their cold-adapted relatives. Beheregaray and his colleagues show that these new hybrid populations are less vulnerable to future warming than the cold-adapted ones.
“Hybridisation can bring greater adaptability to some species,” Beheregaray says. Crucially, he adds, hybridisation is also an area where people can get involved. “We could manage populations at risk by actively bringing in genetic material that might help them adapt,” he says. “It would be better than to sit and watch extinction take place before our eyes.”
Even if animals don’t have the genetic diversity or hybridization potential to weather the coming warming, there are other ways they can adapt, says Ryan Martin, one of Diamond’s CWRU colleagues who also studies evolutionary responses to climate change. Some animals can move, seeking out microhabitats that remain in their preferred temperature range, he says. Or they can adjust their behavior to be more active at cooler times of the day, which might buffer them against the effects of climate change.
But behavioral changes can only be pushed so far, says Martin. An animal that retreats up a mountain to stay cool will eventually run out of mountain, and by then, it may be too late for them to evolve better heat tolerance.
Winners and losers
Ultimately, as the climate continues to warm and species scramble to keep pace, there is going to be a seismic shift in the animal community, says Diamond. Big marine animals like whales, with their small populations and long life spans, will be vulnerable to extinction—as will creatures with temperature-dependent sex ratios, like sea turtles. These animals may not survive a period of rapid warming. But squid and tiny, fast-living copepods will probably manage just fine—they may even thrive.
“There are going to be winners and losers, and some of the losers will be very noticeable,” says Martin.
Beyond anticipating the fates of individual species, though, the really tricky part is knowing what these changes might mean for the ecosystems of the future. “We can make general predictions,” says Diamond, but “we don’t know what the butterfly effect of losing key ecosystem services will be.”
This article first appeared in Hakai Magazine, and is republished here with permission.
