KINGSTON, R.I. – August 16, 2018 – Jason Kolbe has been thinking about hurricanes and lizards for many years.
The University of Rhode Island professor of biological sciences has measured the length of lizard legs and the size of their toe pads to assess how those factors influence the animal's ability to cling to vegetation during strong storms. He even used a powerful leaf blower to test his hypotheses in a laboratory.
"I think a lot about this," he said. "We know that longer limbs and more muscular limbs enable lizards to wrap their arms around branches and get a better grip on the vegetation."
But until the perfect storm of circumstances arose last year, he was never able to field test his ideas.
A postdoctoral colleague at Harvard University happened to measure the limb length and toe pads of lizards on the Turks and Caicos Islands just four days before Hurricane Irma swept through with 165-mile-per-hour winds last September. Two weeks later, Hurricane Maria followed suit.
The storms provided the scientists with the unusual opportunity to see how hurricanes affect the evolution of the lizards. So Kolbe's colleague returned to the islands to measure the surviving lizards just weeks after the hurricanes. Their findings were published last month in the journal Nature.
"Our previous studies suggested that lizards with longer limbs and larger toe pads can cling better, so we expected that the lizards that survived the storms would be those with longer limbs and larger toe pads," Kolbe said. "And our prediction was supported for the toe pads and the forelimbs. But the survivors had shorter hind limbs, which was a surprise."
When the researchers watched the videos they previously made of their experiment with the lizards and the leaf blower, they understood why the surviving lizards had shorter hind limbs.
"When the lizards start to get blown by the wind, their hind limbs lose contact with the vegetation first, so they're holding on only with their forelimbs," he explained. "When they're perched on vegetation, their hind limbs stick out and catch the wind. It turns out that lizards with shorter hind limbs have an advantage in a hurricane."
What does all this have to do with evolution?
"The event we documented seems to be about natural selection. Some lizards lived, some lizards died," Kolbe said. "To translate that to evolutionary change, those surviving lizards have to reproduce and those traits – longer forelimbs, larger toe pads – have to be passed on to their offspring. So we're going back this fall to measure the offspring produced by the surviving lizards."
While the URI scientist is confident the offspring of the surviving lizards will have many of the traits that made their parents successful at surviving hurricanes, there may be other factors at work pushing them to evolve in different – even opposite – ways.
"What's natural selection doing when there isn't a hurricane?" asked Kolbe. "What traits are favored under non-hurricane circumstances? Do their longer limbs now put them at a disadvantage? In between hurricanes, shorter limbs may be favored for moving around on the narrow vegetation."
It may take several generations of lizards and several years between hurricanes for all the questions to be answered. And even then, the expected increase in severe storms due to the changing climate will likely raise even more questions.
"In the past, when there has been a long period of time between hurricanes, the populations recover and natural selection might act to take them back to some optimal state for their environment," Kolbe said. "But if hurricanes keep hitting the island more frequently – making them more susceptible to extinction – selection may start to act in a back and forth fashion, and at some point they might not be able to respond effectively from an evolutionary sense.
"That's the bigger message," he added. "Most populations are experiencing multiple stressors – climate change, habitat change, invasive species – and all those changes are pulling populations in different directions. They might be able to adapt to one of those, but others are forcing them to adapt in another direction. They may end up using up all of their evolutionary fuel."
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