In just 15 years—or 20 lizard generations—green anoles living on islands off Florida's eastern coast have evolved a way to survive with aggressive invaders from Cuba, the brown anoles. Brown anoles and green anoles compete for food, and they will also eat one another's young. To avoid this clash, green anoles took to the higher parts of trees and evolved larger, stickier toe pads to help them get a better grip on that newfound habitat, Science Daily reports.
Researchers from the University of Texas at Austin actually introduced brown anoles to three small, artificial islands—the byproduct of dredging from the 1950s. As The Scientist explains, they studied green anoles' behavior and physiology before and after the introduction of a few of their Cuban rivals and monitored those populations for 15 years. "By August 1995, after just three months, the Carolina anoles began perching at greater heights," The Scientist writes. "On the control islands, however, the Carolina anole was making full use of its typical habitat: the entire tree, from the ground to the crown."
When the lizards' toes started to change in size, shape and stickiness, the scientists performed tests in the lab to see if those traits were inheritable. Offspring of larger-toed individuals did indeed inherit that trait in the lab, The Scientist reports.
The team expected to see some change in the green anoles due to the increased competition, but the extremity of that shift—referred to as character displacement—caught them off guard. "To put this shift in perspective, if human height were evolving as fast as these lizards' toes, the height of an average American man would increase from about 5 foot 9 inches today to about 6 foot 4 inches within 20 generations -- an increase that would make the average U.S. male the height of an NBA shooting guard," lead author Yoel Stuart said in a statement.