Late last year, biologist Colin Donihue traveled to the Turks and Caicos Islands to study an endangered rock iguana. After he and his colleagues finished up their research on Pine Cay and Water Cay, they headed back north.
Less than a week later, disaster struck—two hurricanes rocked the islands, back to back.
“Four days after we left, Hurricane Irma came through,” says Donihue, who’s a postdoctoral fellow at Harvard University and the Paris Natural History Museum. Hurricane Maria followed shortly after. (Photos: See Hurricane Irma’s devastation in Florida and the Caribbean.)
SEE WHY SCIENTISTS ARE USING LEAF BLOWERS TO STUDY NATURAL SELECTION
Scientists collected small-bodied anole lizards and set up a hurricane simulation to study how natural disasters affect animal evolution.
The islands saw massive destruction, but amid the tragedy, Donihue and his team found an opportunity to learn about nature’s resilience. Six weeks later, they returned to the islands to study why certain anole lizards had outlasted the storms. (Related: How Hurricane Irma pushed a rare island species closer to extinction.)
“When we realized that we had this opportunity, we revisited with just a couple hypotheses in mind,” Donihue says. “If there’s anything that helps a lizard survive a hurricane, it would probably be something having to do with how it grips onto surfaces.”
A fallen tree toppled by Hurricane Irma blocks a street in downtown Miami, Florida on September 11.
PHOTOGRAPH BY SAUL LOEB, AFP/GETTY
Holding On for Dear Life
For the experiment, the researchers captured 47 Anolis scriptus lizards and brought them to the lab. Then, they perched each lizard on a thin wooden dowel—a tree branch stand-in—and aimed a leaf blower at it. The scientists gradually increased the machine’s wind speed to mimic hurricane-force gales, which they focused at the lizard until it lost grip of the dowel.
The researchers positioned protective padding and netting behind the lizards to ensure that they weren’t harmed in the experiment. After one trial each, the reptiles were released back into their original habitats.
“Using a leaf blower to simulate hurricane-force winds was very creative, clever, and resourceful,” says Amber Wright, an ecology professor at the University of Hawaii at Manoa. Wright was not involved in the research.
“What makes the study interesting to me is that it links traits to survival through a specific mechanism: Ability to cling to a perch and to be a small target,” Wright continues. This helps biologists predict what will give lizards a leg up in surviving a storm—and ultimately what traits are most likely to be passed on through natural selection.
Donihue and his colleagues thought larger toepads and longer limbs would help the lizards grasp the dowel. They were partially right—the surviving lizards had larger toepads and longer forelimbs, but their hind legs were shorter than their front legs.
“We didn’t have any predictions about what shorter hind legs might mean,” Donihue says.
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VIDEO BY NASA'S GODDARD SPACE FLIGHT CENTER
After analyzing video from the experiment, the researchers noticed that the lizards lost grip of the dowel with their back legs before their longer front legs gave way.
So shouldn’t lizards with longer legs in both front and back be able to hang on even tighter? Donihue says that’s not clear, but there could be tradeoffs to growing larger overall. “Larger lizards are stronger, but they also run the risk of catching more wind,” he says.
Big events, such as storms or the appearance of a new predator, can wipe out large numbers of animals, speeding up the usual process of natural selection in which survivors pass on their genes. For example, rapid selection has been seen in certain mussels whose shells got thicker to protect against predatory crabs, says Tracy Langkilde, a Penn State biologist who was not involved in the research, by email. Also, the head size of some snakes decreased rapidly over generations to protect against invasive toxic cane toads. (Related: How some bird species survived the 2017 hurricane season.)
“Donihue’s study is one of the first to provide evidence that extreme weather events could impose rapid selection on species,” Langkilde continues. “It provides incentive for others to test for these effects on other species.”
Wright adds that although the details of the study can’t necessarily be applied to other species, the methodology is crucial. If researchers study other species with regard to certain environmental changes, future studies could be helpful in understanding how animals respond to natural disasters.
“Being able to generate these kinds of predictions is important for managing populations and developing ways to increase resilience,” Wright says in an email, “in light of predicted increases in extreme events due to climate change.”