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Monday, March 28, 2022

Color Changers

 

Green Anole, Anolis carolinensis

Native to North America and most abundant from the Carolinas south to Florida, along the Gulf Coast, and as far west as the Texas Hill Country, the Green Anole (Anolis carolinensis) is a small to medium sized lizard with a long, pointed head, slender body, long tail, and toes with adhesive pads that facilitate climbing.  Arboreal in nature, it can also be seen on the ground and in areas with shrubs and vines at the edge of our moist forests.

Males are typically 15% larger than females, from 4.9 to 8 inches long, with about 65% of that length being tail. Males have a dewlap or throat fan that is three times the size of the females and is strawberry-red, while the females’ dewlap ranges from white to light pink.  Unlike males, females also have a prominent white stripe that runs along their spine.

Male Green Anole with dewlap extended

Strongly territorial, males will fight other males to defend their territory, and have even been known to fight their own reflection in mirrored glass. When a male sees a rival, he will compress his body, extend his dewlap, inflate a dorsal ridge, and bob his head to chase off the intruder.  If that doesn’t work, they will fight, especially during mating season. A male’s territory typically includes two to three females, and he will court a female by extending his dewlap and bobbing up and down, mimicking a push-up. 

Breeding begins in April and ends in late September, with females laying their first clutch of one or two eggs about a month later.  Females can produce an egg every two weeks during mating season, up to about ten eggs, and they are buried in a shallow depression in soft soil or leaf litter.  Eggs are incubated by the heat of the sun, and hatch in five to seven weeks, with the hatchlings left to fend for themselves.

What is most intriguing about these lizards is their ability to change color from bright lime green to dark brown, and while often called ‘American chameleons’, they are not true chameleons.  Their ability to change color is a result of three layers of pigment cells or chromatophores.  The first is the xanthophores which is responsible for yellow pigmentation, the second is cyanophores responsible for blue pigmentation, and the third is melanophores responsible for brown and black pigmentation.

Male Green Anole, brown color form

If one of the chromatophores is lacking due to genetics, color mutations can form, but are extremely rare in the wild. Blue-phased green anoles lack xanthophores, and yellow-phased green anoles lack cyanophores.  These color exceptions rarely live long, as they don’t provide the camouflage the green color does, which is highly useful in hiding from predators and hunting down prey.

Several factors contribute to the anole changing its color, including its mood, stress level, activity level, and even social signals such as displaying dominance.  Although claimed, evidence does not support color change due to camouflage or a response to background color, and it is even less clear if the color change is in response to temperature.  When stressed, during a fight for example, the skin behind their eyes may turn black and form postocular spots that resemble a small black mask.  

Regardless of the reason, no other lizard species in Texas is capable of such extensive color change.  With populations existing in even the largest of cities, these color changers are a fascinating part of our suburban landscape!