By Dr. Becker
Green anole lizards are a common species native to Florida and other parts of the southeastern US. Ranging in size from five to eight inches, green anoles often live in trees, and have sticky scales (known as adhesive lamellae) on their feet.
Similar to geckos, these sticky scales allow green anoles to cling to tree branches and even scale walls with ease. Green anoles are often bright green in color, but they can also turn a gray or brown color. This shouldn’t be confused with the brown anole lizard, which is not native to Florida but has established itself there nonetheless.
Brown anoles originated in Cuba and the Bahamas, but have made a regular home for themselves in Florida since the 1950s. It’s thought the lizards reached the mainland by stowing away on ships carrying agricultural goods from Cuba.1
Increasing numbers of brown anoles are thought to be responsible for decreasingnumbers of green anoles. The brown anole males may prey upon smaller green anoles, and they’ve become one of the most abundant lizards in Florida.2 Unlike their tree-dwelling green cousins, brown anoles often live on the ground or in low vegetation.
As a result, their prevalence has pushed green anoles up into higher trees, which provides a safe refuge. The green anoles have even developed a special feature that makes their new high-rise living easier…
In Just 15 Years, Stickier Feet Help Green Anoles Scale Tall Trees
Green anoles quickly relocated to higher tree branches when brown anoles came into town. Their feet responded in kind with remarkable evolutionary speed, developing larger toepads and becoming stickier in just 15 years and 20 generations. The study, published in the journal Science, explained:3
“On small islands in Florida, we found that the lizard Anolis carolinensis [green anoles] moved to higher perches following invasion by Anolis sagrei [brown anoles] and, in response, adaptively evolved larger toepads after only 20 generations.
These results illustrate that interspecific interactions between closely related species can drive evolutionary change on observable time scales.”
The changes make it easier for the lizards to grip trees’ smooth upper branches. While the changes themselves weren’t entirely unexpected, the speed at which the changes occurred surprised even the researchers.
Lead researcher Yoel Stuart, a postdoctoral researcher in the Department of Integrative Biology at The University of Texas at Austin, put the quick evolutionary change into perspective:4
“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."
Fun Facts About Green Anole Lizards
These lizards may be small, but they have their fair share of spunk. Sometimes called the “American chameleon,” green anoles can change their color depending on their mood, body temperature, humidity levels, and health. Males have a pink flap of skin that hangs below their neck, known as a dewlap. This is used for protecting territory and attracting females.
Male green anoles are very territorial, so much so that if you place a mirror in front of one, he might become aggressive toward it. They also have a distinctive set of behaviors used for protecting their territory. According to the Smithsonian National Zoological Park:5
“Male anoles perform rituals of dominance and territoriality. They show their dominance by bobbing their heads, usually through pushup-like movements. They also flare their dewlap.
When threatened by another male, the opponents begin with head bobbing and flaring. Then they extend their throat (different than dewlap) to enlarge their body profile, they turn lateral to their opponent, showing the side profile of their body.
They also erect crests along the back, and form an eyespot. These performances are intended to intimidate the other anole. The loser of the confrontation performs submissive head bobbing and retreats to a different territory.”
In the wild, green anoles eat insects and spiders, which can only be detected with movement. While green anoles are not a threatened species, they do face some threats in the wild, namely housecats and being collected for the food trade.6