Video shows lizard hanging on during hurricane-force winds. Large toepads are the key
Strong hurricanes can leave a trail of destruction and hardships to remember them by, but new research shows that these powerful storms also give lizards a long-lasting gift: larger toepads.
Evidence shows that Anolis lizards that frequently deal with hurricanes have larger toepads than those that experience fewer hurricanes, according to a new study published Monday in the journal Proceedings of the National Academy of Sciences.
This is the first paper to indicate hurricanes act as an agent of natural selection, Colin Donihue, lead author of the study and a postdoctoral fellow in biology in Arts and Sciences at Washington University in St. Louis, told McClatchy News.
“Was this a one-off event, or is this actually a pattern that occurs more broadly across lizards as a whole that are affected by hurricanes?” Donihue said. “It depends, but evolutionary changes can happen much more quickly than we ever previously appreciated.”
Donihue and his colleagues were roaming the Turks and Caicos islands in 2017, catching anole lizards for a separate study when Hurricane Irma struck the islands with Category 5 winds up to 170 mph. Two weeks later, Hurricane Maria, another Category 5 storm, released her wrath on the region.
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After returning to the wrecked islands six weeks later, the researchers realized the critters that survived had 5% larger toepads than their predecessors, Donihue said of his 2018 study published in the journal Nature.
It turned out the lizards born after the hurricanes also had larger toepads, meaning the trait was passed down through generations.
“The effect was subtle. It’s not the kind of pattern where you can hold the lizard in your hand from before and after and immediately see the difference,” said Donihue, who had to trace hundreds of photos of lizard toes on a computer to measure them.
“Even just a little increase in toepad area results in a bigger increase in gripping strength, and any increase would be advantageous,” Donihue said.
Toepads help lizards cling to trees, he said, and the larger they are the more area they have to hold on to for dear life during hurricane-force winds.
The video above, which simulates a hurricane using a leaf blower, shows the lizards choose to hold onto trees during a storm, instead of fleeing to enclosed areas, Donihue said. The later would mean their larger toepads have nothing to do with storm survival, he added.
But the researchers wanted to test if this trait had evolved to stay for the long term.
To do this, the team returned 18 months later and compared the single species — Anolis sagrei — found in Turks and Caicos with the same species across 12 other island populations, and again compared those to 188 different Anolis species that live between Florida and Brazil.
The researchers also used 70 years of hurricane data from the National Oceanic and Atmospheric Administration to calculate how many times a hurricane had passed over one of their study locations.
“Hurricanes seem to be having some sort of additive effect on the evolution of these lizards — that the more hurricanes you have, the larger toepads you have, on average,” Donihue said in a press release.
Caribbean anoles are extremely diverse, Donihue said, which makes it easier to compare phylogenetic changes among species. They range between three to 12 inches in size, and can take on almost any color, including browns, bright blues and even some pinks, Donihue said.
These lizards can also live in tree tops, on tiny twigs or somewhere in between, Donihue added. Regardless of their living space, the evidence showed it was still advantageous to have larger toepads.
Scientists have known that Caribbean lizards naturally have larger toepads than those on mainlands, but the “physical difference has never been definitively linked to an evolutionary response to hurricanes,” the press release said.
But, hurricanes are infrequent and unpredictable, Donihue said, “so we expect that there are other selective pressures that are acting on toepads. In other words, over time, these toepads are not going to turn into big snowshoes, or something like that. There’s a balance.”
The researchers tested other possible factors such as tree height, air temperature and rain that could have impacted toepad size, but “found no significant correlations with toepad area,” the study said.
There are also other hurricane attributes such as storm duration, rain, and direction that need to be studied more to understand all selective pressures put on lizards.
Evolutionary biologist Tony Gamble, an associate professor in the department of biological sciences at Marquette University in Wisconsin, told McClatchy News these pressures lead to additional questions.
“Is it that after decades and centuries of hurricanes, this lasting effect could be this gradual increase in toepad size, or are hurricanes affecting vegetation and these patterns are adaptations to vegetation?”
Donihue hopes his study sparks interest into just that: how hurricanes affect the evolution of other species such as trees.
He said that taller trees usually equal larger toepads, according to previous studies, but research also shows that hurricane-prone areas tend to have shorter trees.
As a result, one might expect lizards in regions such as the Caribbean to have smaller toepads, but that’s “the opposite of the trend we observed,” Donihue said.
“For me what really takes this to the next level is that they show how this microevolutionary process can lead to macroevolutionary patterns,” Gamble said.
“I thought this was awesome,” he added. “That’s what slapped me in the face.”
This story was originally published April 27, 2020 at 2:01 PM with the headline "Video shows lizard hanging on during hurricane-force winds. Large toepads are the key."
