Lizards in Florida are evolving right before our very eyes, according to scientists who have tracked the lizards’ evolutionary progress over the past 15 years. In a classic case of natural selection and what biologists call “character displacement,” Florida’s Anolis carolinensis — more commonly known as green or Carolina anole — are being forced to flee to higher grounds as another species of lizards from Cuba invade their habitat.
Due to the threat from the Cuban anoles, who have been swarming Floridan plains for the past few years, the Carolina anole have been pressured to perch on higher trees to avoid these unwanted visitors. As a result, after just a few generations, the local anoles have evolved with better feet, which are more equipped at gripping the thinner, higher branches of the trees. The lizards’ toe pads have evolved to become larger and stickier as well. These allow the reptiles to maintain and secure their positions up above the trees.
What surprised scientists was the incredibly rapid evolutionary change in the Carolina anole physiology, just 15 years and 20 generations after they were first observed to evade the incoming Cuban anoles. Yoel Stuart, a biologist from the University of Texas, Austin, who lead the evolution study, told phys.org that although they predicted some evolutionary change among the lizards, they didn’t expect the degree and speed of the anoles’ evolution.
“We did predict that we’d see a change, but the degree and quickness with which they evolved was surprising.”
To demonstrate the degree by which the lizards evolved after just a few generations, Stuart compared their change to our own.
“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. Although humans live longer than lizards, this rate of change would still be rapid in evolutionary terms.”
The researchers speculate that the competition for food among Cuban and Carolina anoles might have been the primary drive behind the rapid evolution of the latter. Both species also tend to eat the offspring of the other species, sparking a tight territorial battle between the two lizard species.
The study has been published in the latest edition of the prestigious journal Science.
[Images from Cletus Lee/Flickr and Yoel Stuart]