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NGSS: Core Idea: LS4.C, LS4.B

CCSS: Literacy in Science: 8

TEKS: 6.3A, 7.11B, 7.11C, 8.11C, B.7C, B.7D, B.7E

Blowing in the Wind

Scientists investigate whether hurricanes change how lizards grip

SHUTTERSTOCK.COM (CLOUDS, TREES); COURTESY OF COLIN DONIHUE (ALL ANOLE IMAGES)

AS YOU READ, THINK ABOUT how severe weather might affect animal populations.

For a week in the summer of 2017, Colin Donihue and Anthony Herrel hiked around the tropical Atlantic islands of Turks and Caicos. The biologists weren’t on vacation—they were looking for little brown lizards called anoles (uh-NOHLZ) as part of a conservation project. Whenever the pair spotted one of these reptiles, they measured parts of its body and took close-up photos of the bottom of its toes. Anoles have grippy toepads that allow them to cling to surfaces— they can even scurry up smooth windowpanes. 

After collecting data from 71 lizards, the scientists packed up their gear and left the islands. Donihue returned to Harvard University, in Massachusetts, and Herrel to the National Museum of Natural History in Paris, France. A few days later, on September 7, Hurricane Irma struck the region. It battered Turks and Caicos with 265 kilometer (165 mile) per hour winds. Two weeks after that, Hurricane Maria hit the islands, uprooting trees and tearing roofs off buildings. Donihue and Herrel watched the news in horror. 

After making sure their colleagues in the area were safe, the scientists’ thoughts turned to their scaly research subjects. How had anoles weathered the one-two punch of such devastating storms? Donihue and Herrel didn’t know if anoles had any adaptations that might help them survive hurricanes. But the scientists realized that by visiting the islands before the storms, they’d already done some of the legwork needed to find out. The researchers quickly planned a return visit. “As soon as the airport opened,” says Herrel, “we flew back out to get some data.” 

For a week in the summer of 2017, Colin Donihue and Anthony Herrel were out hiking. The biologists were in the tropical Atlantic islands of Turks and Caicos. But they weren’t on vacation. They were looking for little brown lizards called anoles (uh-NOHLZ) as part of a conservation project. Whenever they spotted one, they measured parts of its body. They also took close-up photos of the bottom of the lizard’s toes. Anoles have grippy toepads that allow them to cling to surfaces. They can even scurry up smooth windowpanes!

After collecting data from 71 lizards, the scientists packed up their gear and left. Donihue returned to Harvard University, in Massachusetts. Herrel went back to the National Museum of Natural History in Paris, France. A few days later, on September 7, Hurricane Irma struck the region. It battered Turks and Caicos with 265 kilometer (165 mile) per hour winds. Two weeks after that, Hurricane Maria hit the islands. The storm uprooted trees and tore roofs off buildings. Donihue and Herrel watched the news in horror. 

After making sure their colleagues in the area were safe, the scientists thought about their scaly research subjects. How had anoles weathered the storms? Donihue and Herrel didn’t know if anoles had any adaptations that might help them survive hurricanes. But they realized that their previous visit could help them find out. The researchers quickly planned a return trip. “As soon as the airport opened,” says Herrel, “we flew back out to get some data.”

AFTER THE STORMS 

When the scientists arrived back in the region, the hurricanes’ effects were obvious. On the island of St. Maarten, Herrel waited for his next flight in a tent because the airport terminal had been destroyed. In Turks and Caicos, many buildings had lost their roofs. But natural vegetation was already regrowing. “I was pleasantly surprised at how good the environment looked,” says Donihue. 

The scientists were also happy to find lizards that had survived the storms. They used a tool called a digital caliper to measure the dimensions of the animals’ bodies and limbs. They also used a scanner that plugged into a cell phone to collect images of their toepads. The researchers gathered this data from 93 lizards—and as they analyzed it, a clear pattern began to emerge. 

Donihue and Herrel discovered that the lizards that survived the hurricanes had larger toepads, longer front legs, and shorter back legs than the general pre-storm population. The findings suggested that those traits, or characteristics, may have helped some lizards ride out the storms. But how? 

When the scientists arrived back in the islands, they could see changes from the storms. On the island of St. Maarten, Herrel waited for his next flight in a tent. The airport terminal had been destroyed. In Turks and Caicos, many buildings had lost their roofs. But wild plants were already regrowing. “I was pleasantly surprised at how good the environment looked,” says Donihue. 

The scientists were also happy to find lizards that had survived the storms. They used a tool called a digital caliper to study these lizards. It helped the scientists measure the animals’ bodies and limbs. They also used a scanner that plugged into a phone to collect images of their toepads. The researchers gathered data from 93 lizards. As they analyzed it, a clear pattern began to emerge.

Donihue and Herrel discovered that the lizards that survived the hurricanes had larger toepads, longer front legs, and shorter back legs than the population from before the storms. Those traits, or characteristics, may have helped some lizards ride out the storms. But how?

COURTESY OF COLIN DONIHUE

SURVIVAL FEATURE: Big toepads on their front feet help lizards grip branches in high winds. 

HOMEMADE HURRICANE 

Donihue and Herrel weren’t sure how anoles behaved during a hurricane. Did they drop to the ground and seek shelter? Or did they cling to branches for dear life? Donihue came up with a way to investigate these questions. It started with a trip to the hardware store to buy the strongest leaf blower he could find. 

The scientists used the leaf blower to simulate hurricane winds in a makeshift lab on the front porch of the home where they were staying (see Test Setup). One at a time, they placed anoles collected from the wild onto an artificial wooden perch. Then the researchers pointed the leaf blower at each animal and gradually cranked up the power. They recorded slow-motion video until each lizard flew off the perch— landing safely in a nearby net. 

Donihue and Herrel weren’t sure how anoles behaved during a hurricane. Did they drop to the ground and seek shelter? Or did they cling to branches for dear life? Donihue came up with a way to find out. It started with a trip to the hardware store to buy the strongest leaf blower he could find.

The scientists used the leaf blower to simulate hurricane winds. They set up a makeshift lab on the front porch of the house where they were staying (see Test Setup). One at a time, they placed wild lizards onto an artificial wooden perch. Then the researchers pointed the leaf blower at each animal. They gradually cranked up the power. They recorded slow-motion video until each lizard flew off the perch. The lizards landed safely in a nearby net.

The anoles didn’t seem bothered, says Donihue. “I like to think they were bored—like, ‘Ugh, a third hurricane?’” he says. But the videos revealed that the lizards weren’t purposefully letting go of the fake branch. They clung on until the blast of air overpowered them. The scientists inferred that longer, stronger front legs and larger toepads were adaptations that helped the lizards hold on (see Changing Feet). 

The footage also showed that the lizards’ back legs dangled in the wind as they held on with their front feet. The scientists surmised that shorter hind legs were less likely to get caught by the wind and cause a lizard to lose its grip—another adaptation improving its odds of survival. 

The anoles didn’t seem bothered, says Donihue. “I like to think they were bored—like, ‘Ugh, a third hurricane?’” he says. But the videos revealed something interesting. The lizards weren’t letting go of the fake branch on purpose. They clung on until the blast of air pushed them off. The scientists made an inference from this observation: Longer, stronger front legs and larger toepads helped the lizards hold on. These features were adaptations, they thought (see Changing Feet).

The footage also showed that the lizards’ back legs dangled in the wind as they held on with their front feet. The scientists thought that shorter hind legs were less likely to get caught by the wind. That would cause a lizard to lose its grip. Shorter back legs seemed like another adaptation improving its odds of survival. 

THE BIG PICTURE 

Donihue and Herrel were thrilled with their results. But they had more questions. For example, were storms actually influencing the anoles’ evolution—change in a species’ traits over time? 

To find out, the scientists made one more trip to the tropical Atlantic in 2019. They measured anoles from Turks and Caicos, as well as other nearby islands, and gathered historical weather records. It turned out that the more storms a lizard population had experienced over the past 70 years, the bigger its toepads were. 

That supported their hunch that hurricanes are a driving force for natural selection—the process by which organisms better adapted to their environments tend to survive longer and produce more offspring. For Donihue, now at Brown University in Rhode Island, it’s also an important example of serendipity in science. “We were in the right place at the right time,” he says, “and that ended up giving us all sorts of insights."

Donihue and Herrel were very happy with their results. But they had more questions. For example, were storms actually influencing the anoles’ evolution—change in a species’ traits over time?

To find out, the scientists made one more trip to the tropical Atlantic and Caribbean in 2019. The researchers measured anoles from Turks and Caicos. They also measured lizards on other islands nearby. And they gathered past weather records. The more storms a lizard population had experienced over the past 70 years, the bigger its toepads were. 

That supported their hunch that hurricanes are a force for natural selection. It’s the process by which organisms better adapted to their environments tend to survive longer and produce more offspring. For Donihue, now at Brown University in Rhode Island, it’s also an important example of luck in science. “We were in the right place at the right time,” he says, “and that ended up giving us all sorts of insights.”  

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