Near Baja California, Mexico, the tropical sun warms shallow tidal pools to temperatures well over a hundred degrees Fahrenheit. Yet even in this extreme environment, tiny crustaceans called tidepool copepods thrive.
Surprisingly, these Mexican copepods can handle temperatures about seven degrees hotter than populations of the same species in northern California. Even so, in laboratory experiments, the Mexican copepods quickly die when exposed to hotter water.
As the "organisms heat up, their proteins actually begin to melt,” says Morgan Kelly, a biology professor at Louisiana State University who studies the two-millimeter-long crustaceans. (Read about the animals can can live in the hottest places on Earth.)
It’s a sobering clue into how the planet’s species—from the smallest insects to the largest mammals—are struggling to cope with a rapidly warming planet. Earth’s global temperature has risen about two degrees Fahrenheit since 1880, and the rate of warming is more than twice as fast today as it was in 1981.
There is hope for some animals, however. City-dwelling acorn ants can evolve over multiple generations to tolerate up to three more degrees Fahrenheit, from 115 to 118.
“Evolution gives you an important buffer,” says Sarah Diamond, an associate professor of biology at Case Western Reserve University in Ohio who studied the ants.
“While evolution on its own might not be enough to keep pace with climate change for a lot of the species we’ve studied so far, it can buy us more time.”
Some like it hot
Many species have clever adaptations to handle heat, particularly those in arid desert environments. Creatures like the Sphincterochila snail can tolerate the direct sun of southern Israel’s desert for up to a few hours in 131-degree temperatures, and for much longer at 122 degrees. They remain dormant in the heat, saving energy until rainy periods when they eat and reproduce.
The Rüppell’s fox makes a living in Iran’s Lut Desert, where the mercury has hit almost 160. The predator only hunts at night, when the weather cools down.
The Saharan silver ant builds underground lairs to escape temperatures of 120 degrees, and only comes out briefly to grab food.
Domestic donkeys and their ancestor, the wild ass, evolved to hoard resources instead of mates. The solitary African wild ass, a critically endangered species native to the Horn of Africa, will guard a watering hole, and mate with any arriving females, says Fiona Marshall, an archaeologist at Washington University in St. Louis who has long studied domestication of African animals and climatic shifts.
“Everyone complains donkeys are stubborn, but they’re used to being solitary and making their own decisions,” Marshall says. (Read more about how climate change is impacting the natural world.)
Living in a herd works for animals in wetter, lusher places where there’s plenty of food and water to go around. It’s not great for sparse deserts.
Other adaptations are much more physical. The moist inner lining of a camel’s massive nostrils can extract moisture from air as the animal breathes in or out.
Other desert animals, such as kangaroo rats and wombats, pull every bit of moisture from food, depositing dry feces.
“Time is running out”
So are heat-adapted species better suited to survive an increasingly hot planet, or are they just as out of luck as the rest of us?
It depends, researchers say. (Read how extreme heat can trigger die-offs for some animals in the American West.)
As a general rule, the smaller, more widespread, and less complex an organism, the quicker it can adjust to change.
That’s why a species like deer mice would have more opportunities to evolve enhanced adaptions to heat than, say, endangered elephants, says Martha Muñoz, a biology professor at Yale University in Connecticut. Larger populations often provide greater genetic variation for tinkering.
Secondly, evolution requires time. A bacterium can reproduce six times a day, creating plenty of quick turnover. Blue whales, on the other hand, can take up to 15 years to reproduce.
Some species can change their behavior when faced with hotter temperatures—though even that has consequences.
Muñoz and colleagues found that Anolis lizards living on the edges of Caribbean forests where they can move between warmer and cooler spots—like hiding under boulders in the heat of the day—did not bother changing their metabolism or other physiological factors when temperatures increased. That ultimately diminished their future generations' ability to do so.
Their forest brethren, however, increased their baseline heat tolerance, and were better able to survive. This evolutionary phenomenon even has a name: the Bogert effect.
She has also found, as with acorn ants, that some species can evolve quickly. In one study, the montane horned lizard in Mexico increased its heat threshold by about 1.8 degrees Fahrenheit following a year of heat waves.
But despite such remarkable adaptations, Muñoz warns they’re not nearly quick enough to keep up with the rate of our planet’s warming.
These animals are “existing on borrowed time, and time is running out."