Decades ago, the evolutionary biologist Jonathan Losos found himself chasing a lizard around an island in the Bahamas. The island was little more than mound of craggy limestone the size of a baseball diamond, and Losos, an evolutionary biologist at Washington University in St. Louis, stepped carefully around the many holes in the ground in pursuit of the reptile, which was a kind of lizard called an anole. He carried his lizard lasso, a fishing pole tipped with a loop of dental floss. "If you can maneuver the lasso over the lizard's head and then give it a quick pull," Losos said, the lizard is yours. (Lassoing does not hurt a lizard.)
This lizard eluded Losos for a long time. "She's really wily and moving around and staying just out of reach," he said. "I don't think much of it, other than, boy, this is a tricky one." But when Losos finally caught the lizard, he was amazed. "She's missing an entire hind leg," he said. "The wound is healed completely over, and she's fat and sassy."
When Losos saw the colorful bands of non-toxic latex that scientists use to mark individual lizards, he realized that he had caught the same lizard the year before, back when she had four legs. Now she had three, but she was still going strong. Her capture sparked the inspiration for a pet project documenting three-legged lizards that Losos and more than 50 co-authors recently published in the journal The American Naturalist.
Losos was stunned not just by the fact that the lizard had survived, but that she appeared to be thriving. He'd studied lizard legs before, finding that ground-dwelling lizards had relatively longer and stronger legs that helped them escape predators more easily, while tree-dwelling lizards had shorter legs that made them more nimble in branches. In other words, his body of research suggested that even minute changes to a lizard's legs could drastically impact a species' survival. So Losos was perplexed. "It didn't make sense," he said. "If a little bit of leg length is important, missing entire leg should be catastrophic." But despite this anole's trials and tribulations, she remained both fat and sassy.
When I asked Losos how to tell if a lizard was fat and sassy, he assured me it was easy. "You can tell a lizard's condition by basically how plump it is," he said. Some are kind of emaciated, while others are bulbous and bulky, a sign that they've been eating well. "As for the sassy part, it's just that she was moving around and active and being difficult to catch," he said, adding that these were signs she was in good health.
After Losos's encounter with the anole, he started telling friends and colleagues in the lizard community about the three-legged reptile, and asking if they'd seen any like her. Many had. Losos began collecting word-of-mouth records of three-legged lizards, many of whom researchers had observed but had left out of their papers. He talked about this project so much that strangers began reaching out to share their own three-legged lizard encounters, having heard of Losos from their own friends. Losos also posted on a community blog, Anole (pronounced like "annal") Annals (pronounced like "anoles") to report the lizards he'd found and solicit more reports.
When the evolutionary biologist James Stroud joined Losos's lab, Stroud began organizing and analyzing these records, pushing the paper over the finish line. Each of the paper's many authors contributed reports of three-legged lizards from all over the world, resulting in 122 records of lizards that have lost at least an entire foot. The lizards were just as likely to have a damaged forelimb as a damaged hindlimb, which surprised the researchers given how hindlimbs allow lizards to sprint at maximum speed. The researchers only found five lizards that had suffered damage to two or more limbs, and in every case the damaged limbs were on opposite sides of the body. Because these observations were collected opportunistically, the researchers could not draw strong conclusions around how common three-legged lizards are in any population of lizards.
At some point, Losos and Stroud decided to try and catch a three-legged lizard to film on a high-speed camera to see how the reptile moved. Karen Cusick, a retired teacher in Florida and an author on the new paper, had a blog where she documented the animals in her backyard; occasionally, Cusick's lizard photos would make it on Anole Annals. Cusick had recently found a brown anole pinned under the lid of a dumpster. When she freed the lizard, she saw that his leg had been mangled. Over the next week, Cusick watched as the lizard's leg withered away and eventually fell off. The anole appeared to still be in tip-top shape; three days after this accidental amputation, Cusick saw the lizard mating with a large female and inflating his bright throat flap to ward off other males. "I said, I gotta come down and catch that lizard," Losos said.
Cusick invited Losos to lasso in her backyard. "She told me, 'The lizard is always there. You'll have no trouble,'" he said. He flew down at the end of the semester, rented a car, and drove to Cusick's home with a ticket to fly home that night. Once in the backyard, Losos could not find the anole. "It was very stressful," he said. As he and Cusick took a break for dinner, Losos wracked his brain wondering if he should change his flight and get a hotel room.
But when he went out for one last try, the sun low in the late afternoon sky, the anole was out, resting by a thicket of worryingly high grass. "If I disturbed him and he jumped, it was game over," Losos said. He approached carefully and managed to lasso the lizard, popped him in a plastic container in his backpack, and headed to the airport. I asked Losos if he had any trouble taking a Tupperware-bound lizard through security. "I don't think you're supposed to do that," he said, but added he had no problems.
This anole, Lizard 38, became the star of the high-speed footage of three-legged lizard running. Although Lizard 38 had lost more than half of its right hindlimb, it ran even faster than expected for its body size. When the researchers analyzed the video, they found the anole exaggerated the undulations of its body to compensate for its lack of foot. In fact when the researchers tested the running speeds of five three-legged lizards, two ran at the same speed as four-legged counterparts, two ran more quickly, and one ran slower. "It's hard to fathom how it is that a lizard can have such a major change and alter its mechanics to seemingly completely compensate," he said. "That I did not predict."
Of course, the new paper does not suggest that losing a leg does not matter for a lizard. "Probably usually it is catastrophic, but those lizards die and we never see them," Losos said. But he was fascinated by these results, and is curious to learn more about what distinguishes the lizards that survive from the lizards who don't. Some of these factors may exist on an individual basis, perhaps related to a particular lizard's athleticism or sensory capabilities—or, as we like to say in the business, having been Built Different.
Of the lizards recorded in the study, some lived remarkably long lives. One green anole from Tennessee that lost its lower forelimb was the longest-lived animal of its population. One male eastern collared lizard from Missouri with a missing forelimb lived more than four years, exceeding the expected lifespan of males in that population. Although three-legged animals are not a rare sight for most people—three-legged dogs and cats get around just fine—Losos is still struck by the lizards' ability to forage and hunt successfully in the wild. He hopes this new paper inspires other researchers to gather data sets on three-legged animals of other species, such as frogs or lions. He'd like to get sense of how common this might be across the animal kingdom, or if lizards are special in this regard.
To Losos, the most important message of the paper is that natural selection is not the all-powerful force we make it out to be. Scientists spend a lot of time studying how exquisitely adapted animals are to their environments, how cheetahs can sprint at high speeds and hummingbirds can hover with tremendous agility. But this prowess and this perfection are not always necessary for a good life. "Sometime they're just good enough, or even not that good at all, but they can still get by," he said.
After Lizard 38 passed his sprinting test, he headed to someone's terrarium for his retirement. "Had a good long life," Losos said, by which he almost certainly means that Lizard 38 died fat and sassy.
