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Natural selection can occur in a span of mere months—as some short-legged lizards learned the hard way.
Jonathan B. Losos ’84, a professor in the organismic and evolutionary biology department, observed rapid changes in a lizard species within a single generation due to natural selection. The findings, reported in Science this week, illustrate that “processes seen in the short-term can account for evolution over millions of years,” Losos said.
“Contrary to what many people think, you can make predictions about evolution and test them experimentally,” he added.
Losos, a former Crimson editor, studied the lizard species Anolis sagrei for a year and a half while in the Bahamas.
Losos said he and his colleagues observed the lizards on 12 small islands in the Bahamas, introducing a predatory lizard, Leiocephalus Carinatus, onto half of them.
On the islands exposed to the predator, Losos predicted that natural selection would initially favor the longer-legged lizards because they could more successfully avoid the predator. After six months, results showed that the surviving lizards did indeed have longer legs than those on the predator-free islands.
But Losos said that as the lizards became more arboreal in an attempt to avoid the predator, natural selection would favor shorter-legged lizards, who would be more adept at maneuvering in trees.
Six more months of study confirmed that the surviving lizards were now shorter-legged than those on the predator-free islands.
The “rapidity with which the reversal occurred was most interesting,” Losos said in a phone interview yesterday.
Though a hurricane wiped out his Anolis Sagrei population and cut his experiment short, Losos said he intends to reintroduce the predator within a year to repeat his experiment.
Losos also defended introducing the predator onto previously uninhabited land.
“Some people think this is a terrible thing,” he said. But lizard-eaters naturally live just 100 or 200 meters away from the predator-free islands, and “the predators have even been seen to colonize these little islands naturally. We’re merely re-creating what is out there.”
—Staff writer Christina G. Vangelakos can be reached at cvangel@fas.
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