They are of a most glorious Green, and very tame. There are several other Colours of these Lizards; but none so beautiful as the green ones are.
~John Lawson, in A New Voyage to Carolina, 1709
I went for a walk in the yard earlier this week, looking for anything that might be out and about in this wet and warm weather. There are still a lot of insects and spiders that are hanging on as we have not had a truly killing frost as yet. Brushing up against some hickory saplings growing inside the deer fence (there are none outside the fence), I caught a slight movement.
It was a Green Anole, Anolis carolinensis. Well, in name it is green, but that day, it was brown. As you probably are aware, the Green Anole has the ability to completely change colors in just a few minutes. You may hear that it is so they can match their green or brown background. And many people call them “chameleons”. But, they are not a true chameleon and are more closely related to iguanas. And, their color changing behavior is much more complex than simple camouflage.
I found an older photo of an anole from the summer months and posted it above to show how bright green they can appear.
The one this week was almost all brown, except for the scales around its eyes. It was a misty morning with temperatures in the 60’s, but the dampness made it seem cooler, so I was a little surprised to see one out. Even so, this one was moving slowly.
As it climbed over the top of some yellow leaves, I could see the tiny jewel-like water droplets beaded up on its back.
It moved to another leaf, which bent down with the weight of the tiny dinosaur, before the lizard popped its head back up to make sure I wasn’t getting any closer. That’s when the eye shadow really struck me.
Though subtle, the blues, greens, and yellows stood out against the soft brown of the other scales on the head.
The photo above was taken about 6 minutes after the previous one. I have observed in the past a similar color change in the entire body of a Green Anole. This rapid color change has fascinated the public and scientists for a long time. Perhaps, because of this interest, and the relative ease of keeping this species in the lab, physiological color change has apparently been studied more thoroughly in Anolis carolinensis than in any other vertebrate. So, how do they do it, and why? That turns out to be a bit complicated, at least as far as I can comprehend.
After reading several online resources, the best I can come up with is that the color change arises from light reflecting through the epidermis onto three layers of pigmented cells, called chromatophores, with each layer having a different name and being responsible for different color variations. From nearest the skin surface moving downward, the layers are one for blue (which technically has stacks of platelets that reflect blue-green light, instead of blue pigments), one for yellow (yellow and blue equals green), and one for brown. The lizards are able to change color in response to many factors including temperature, stress, and various other behavioral (especially social interactions) and environmental factors. Cooler temperatures, or more stressful conditions, lead to brown colors whereas warm temperatures and the lack of stress leads to the lizard’s being green. If I understand it correctly, this rapid color change is controlled by hormones released by the pituitary gland. When stressed, production of a hormone moves brown pigment granules to the surface, obscuring the blues and yellows beneath, and changing the overall color from green to brown.
I attempted to gather this information from a variety of online resources, but invariably got bogged down in scientific nomenclature like the following sentence: In this species, dermal chromatophores are known to be free of sympathetic innervation, leaving body color subject only to the influence of circulating chromo-active hormones: epinephrine (EPI), norepinephrine (NE) and melanotropin (MSH). I’m sure that is meaningful if you study such things, but I was getting lost. Then, I discovered an amazingly comprehensive community blog entitled, Anole Annals, written and edited by scientists who study Anolis lizards. They did a good job of synthesizing information in a more palatable form. I am constantly amazed (and impressed) by the availability of information and by the dedication and passion of those responsible for researching it and posting it on the web. I did not know until reading this site that the Carolina Anole is the first reptile to have had its genome sequenced. It seems that this species is one of the most studied reptiles in the world in a wide range of disciplines including physiology, behavior, ecology, and other subjects. Many of the studies have implications for human health and behavior.. There is even a citizen scientist page on that site so you can contribute your personal anole observations.
No wonder my little anole started to doze off after several minutes of our photo session. She and her kind have been subjected to scientific research and public fascination for a very long time. She may need the rest. And, it seems like there is still a lot of research to be done.
I’ve spent my entire professional career studying anoles and have discovered that the more I learn about anoles, the more I realize I don’t know.
~Jonathan Losos, Anole Annals
By the way, if you didn’t do it as you read through, you really should go back and click on a few of the photos, especially the close ups of the head, in order to really appreciate the subtle colors. And check out that ear opening while you are at it.