“I wasn’t really sure what to expect,” Donihue says. He found that the islands had clearly taken a severe hit, but were also rebounding quickly. Many trees had been uprooted and stripped bare, but those that had survived were already putting out new leaves. And among the fresh greenery, there were anoles.
The lizards can be found throughout the Caribbean, clinging to twigs and tree trunks with their sticky toes. Whenever Donihue spotted the lizards, he would lasso them with loops of string at the end of modified fishing poles. (“It doesn’t hurt them, because they have very strong neck muscles,” he says. “It’s much easier than running up and grabbing them with your hands.”)
“To be honest, given how catastrophic hurricanes are, I thought it was plausible that survival would be random—that there wouldn’t be an advantage that would help [the lizards] survive,” he says. But when he compared the survivors’ measurements with those of the pre-hurricane population, he realized he was wrong.
He found that, on average, the post-hurricane lizards had toe pads that were 6 to 9 percent bigger than those of pre-hurricane individuals, and front legs that were 2 percent longer. This wasn’t because the bodies of specific lizards had changed; there’s no evidence that the toes of adult anoles can grow by that amount. Instead, the storms had simply wiped out all the lizards with small toe pads. By selecting for individuals that were better at clinging to surfaces—and presumably at withstanding high winds—the storms had changed the average proportions of the population.
These sound like small changes, but natural selection famously works on small physical variations, favoring some over others across many generations. “The changes were subtle, and we couldn’t have noticed them just by holding the lizards in our hands,” Donihue says. “But they were consistent between the two island populations, which makes us feel more confident that this wasn’t a fluke.” The variation in the toe and leg measurements narrowed after the storms, too, adding further evidence that the hurricanes had selected for lizards with particular kinds of bodies.
But one trend didn’t make sense: After the hurricanes, the average length of the lizards’ hind legs was 6 percent shorter than before—the opposite pattern from their front legs. “This was a real head-scratcher,” Donihue says.
He and his colleagues worked out what had happened by placing the lizards on small wooden posts and subjecting them to gusts from “the largest leaf blower we could find,” he says. The lizards would shimmy to the sheltered side of the posts, tuck their front legs close to their bodies, and cling for dear life. But because of the way their legs are structured, their hind thighs would always jut out. These exposed thighs caught the wind like sails, and would eventually rip the lizards from their secure footing (and into the safety nets the team had set up).