An orange Anolis sagrei used in the study. Image by Beth Reinke.
Readers of Anole Annals know that Florida populations of Anolis sagrei now include red-orange individuals [1, 2, 3]. I learned more about this new color by conducting the first scientific study on orange skin coloration in Anolis sagrei.
Before I go any further, I owe a thank you to those who documented their orange A. sagrei findings on Anole Annals. Previous posts confirmed that what I was seeing in the lab wasn’t an anomaly. As I learned more about the sightings of these orange anoles, it became apparent that the orange phenotype was rather common. The posts also helped me understand when this odd coloration was first noticed (only in the last decade!). I was even able to meet with one contributor in person.
The first thing I noticed was that there is quite a bit of diversity in the distribution of orange coloration on the bodies of the lizards themselves. Most of the posts on Anole Annals showcase full-bodied orange lizards [1, 2, 3]. I found that partial orange coloration was just as common. Take, for example, this male whose orange coloration was limited to his tail and hind legs.
A biologist’s first intuition is to wonder how differences in coloration might influence survival. Most of my research project was focused on identifying fitness differences between brown and orange lizards. I was working under the impression that orange skin suddenly appeared in the population and became common very quickly. I knew that there are cases when new phenotypes become common for no reason (genetic drift). Nonetheless, we don’t normally expect to see a new phenotype become common in a short amount of time. I suspected that orange lizards had an easier time surviving or breeding than the brown ones. But I was surprised that a color as conspicuous as orange could be so successful. I reasoned that it couldn’t have helped them camouflage, so why are orange lizards surviving and reproducing?
Maybe it had something to do with mate choice. Since males use their orange dewlaps to attract females, it might be that a completely orange male would look particularly stunning to a female. Even though orange might have made the males an easier target for predators, the effect on reproductive success may have outweighed the risk of predation. This is the hypothesis that I had in mind for most of the project and the one that made the most sense to me. It’s fitting, then, that when I ran a behavioral experiment in the lab, the females didn’t care at all about color! They were much more interested in males that performed a lot of pushups and head bobs (behaviors that many species of lizards use to communicate). These pushups and head bobs demonstrate a male’s physical fitness to a female.
Maybe orange reflected something in their physiology, then? I ran two different experiments to test endurance and sprint speed. The tests of endurance and sprint speed in particular took up most of the time of the project; it turns out live animals don’t usually do what you need them to do. Despite their penchant for sprinting out of sight in the wild, getting lizards to run in the lab was more difficult than you might guess. The endurance tests involved a custom-built lizard-sized treadmill. More often than not, the lizards would treat it like a moving sidewalk you’d find at the airport. Other times they’d wriggle into the machine itself (at no risk to them) and I’d have to take apart the treadmill, one screw at a time, to fish them out. No images of that, sadly.
To measure sprint speed, I needed the lizards to run up a wooden pole. Here’s a video of me trying to convince lizards to run up that pole.
I became more interested in paleontology after this project. Dead animals behave more predictably.
After all that, the data didn’t point to any difference in orange and brown lizards’ endurance or sprinting ability. I took a step back to get to the bottom of something I knew I could answer. I wanted to identify the pigments that they were using to color their skin. Having read about what gives Anolis sagrei dewlaps their red and orange color, I was expecting to see two classes of pigments in orange lizard skin: carotenoids and pterins. No one had extracted pigments from even brown A. sagrei skin before, but I wasn’t expecting to see much in non-orange skin.
I boiled lizard skin in all sorts of carcinogenic solutions to extract the pigments.
Then I separated the two types of pigments in test tubes – carotenoids at the top and pterins at the bottom.
As expected, the dewlaps had both types of pigments. Unexpectedly, brown lizard skin contained pterins. I thought this was a little odd since we don’t see red or orange on brown lizards. But, no one had done this before, so I didn’t quite know what to expect. Like brown lizard skin, orange lizard skin had pterins, but not carotenoids. This surprised me because it suggested that the orange color in orange lizards might not be due to the addition of a pigment so much as the absence of one. Melanin (another class of pigment that produces brown and black colors) typically masks the effects of other pigments that may be present. So, although I was unable to test this myself, I now suspect that the orange color is caused by a lack of melanin.
It was time to revisit that camouflage idea. I had taken for granted that orange was too conspicuous to conceal a lizard, but I needed the data to back up my claim. I collected quantitative data on brown and orange lizards’ skin color by using a spectrophotometer, which records color as the wavelengths of light reflected off a surface. The result is something that looks like this:
What A. sagrei dewlaps look like to a spectrophotometer.
One of my collaborators, Dr. Beth Reinke, applied these data to a visual model to predict how A. sagrei’s bird predators would see the new color. She identified that orange anoles are less conspicuous to bird predators. Now the strongest lead is what I had ruled out when I first began the project: camouflage!
So what’s up with orange A. sagrei? The color doesn’t make them more attractive to mates nor does it correlate to increased physical fitness. Because orange and brown skin contain the same kind of orange-producing pigment, my best guess for the mechanism is a lack of melanin in the areas that appear orange. And, although the new color looks conspicuous to humans, it may help orange individuals hide from bird predators. The benefits of orange as camouflage may explain why the new color persists in south-Floridian populations of A. sagrei.
There’s a lot left to know about orange anoles. A good next step would be to test the “orange as camouflage” result in the field. Additionally, research into the genetic basis of this phenotype may identify how it arose and the mechanism behind it. Some breeders have suggested that orange coloration is genetically dominant over brown coloration. This is something I wanted to identify in breeding experiments, but time ran out before I graduated from college.
Orange A. sagrei remain enigmatic. I hope to hear more about orange anoles from enthusiasts in the lab and the field!
Paper: Erritouni YR, Reinke BA, Calsbeek R (2018) A novel body coloration phenotype in Anolis sagrei: Implications for physiology, fitness, and predation. PLoS ONE 13(12): e0209261. https://doi.org/10.1371/journal.pone.0209261
- Why Are Some Brown Anoles Orange? A Laboratory Study - March 19, 2019
JODIE M WIGGINS
Yes! I’ve suspected a lack of melanin is important in producing the orange coloration in C. collaris as well. I think this study also, once again, highlights the importance of pterins in lizard color and provides a potential avenue for more fruitfully investigating the genetic underpinnings of orange/red color in non-avian reptiles.
Philip M. Fortman
Regarding the recent observations of orange pigmented A. sagrei, there has been a change in the physical environment in the form of the extensive use of red colored ground mulch in Florida’s cultivated landscaping. The photo shown in the e-mail is one example. The adoption of orange coloration may not be entirely driven for attraction, but an adaptation for camoflage. Include information on where the orange A. sagrei are observed and the immediate environment they inhabit.
Pat Shipman
Wow! Great study!
Geoffrey Kemp
I just saw my first red/orange A. sagrei on a walk in Fort Lauderdale! One bold male allowed me to take several photographs, and a smaller very bright red specimen scampered through the grass to it’s bush fortress. Of course, I am trying to find out as much about them as possible, which isn’t much!
Terry Dunham
Hi bred multiple recessive color mutations of several Colubrid snake species for more than a decade. The hypomelanistic explanation makes a lot of sense. But in all of the snakes I worked with, a gene change like that would result in the pigment change over the animal’s entire body, not in isolated areas or with progressive degrees of change.
PS: is there a range map that shows where these orange specimens are occurring?
Bryce
I don’t breed these in captivity but in the yard. I doubt the lack of melanin makes sense since this gene has caused the more normal looking anoles to have pink undertones. The original breeder of them told me second generations from the orange have a pink hue, but then will produce pink, normal, and orange offspring. You won’t find a regular normal in my yard at all now. They also seem to demonstrate a lack of fear. Even the cat doesn’t scare them. In my landscape, they blend perfectly with exotic barks and fallen live oak leaves.
Tova Hooper
I love our orange anole. We named him “Rusty”. He has lived in our yard, partial to a purple passion vine, for a year and a half. His wife’s name is Donna and they have several children, one looked like a mini-Rusty with white under his chin (Rusty does not have white). He must have been hiding out, hibernating, this winter and I feared he was gone. But he is BACK!! And now we noticed two other brown anoles, very very dark in color — black-looking, with white speckles. Very cool to see, but, there was an epic battle on the garden hose between Rusty and one of the interlopers that I was able to capture on iPhone video. Rusty did not appear to be winning, the other lizard was quite aggressive. But they both fell from the hose into the tall grass beneath and both survived to battle another day.
We are so protective of Rusty. A curly-tail had moved in and I wanted my husband to relocate him. Somehow, he disappeared (we also have a black racer who comes by from time to time and searches the vines for a meal – perhaps he was an easy victim as the curly-tail is always on the ground). But, like others state of the orange variety, they are very bold. You can get so much closer than any of the other anoles. I am unsure why that would be, but it is a fact.
Rusty is out little buddy. Sometimes he comes up to the sliding glass door and peers into the kitchen. He also slept on the same leafy area just outside our door for weeks. which allowed me to say goodnight to him and take his photo numerous times.
I am in SE Florida, Palm Beach County.
Leiza
I just spotted a red anole in the palm grass ground cover. Upon closer inspection, it was brownish around the head area, and became increasingly red towards the tail. It had an exceptionally long tail, but aside from that and being red (more red than orange), it looked like one of the typical brown anoles in our yard. We are in north-central Florida, Marion county. We don’t use reddish or orange mulch, neither do our neighbors. We do have a passion vine, though this anole was hanging out in the palm grass and cast iron plants under a canopy of live oaks, magnolias, azaleas, loquats and camellias.
Josh Freeman
I have just recently seen 4 different brown anoles that are red-orange. I pay attention to this, because I enjoy watching them and these are the first that I have ever seen. I was thinking a new food source, but the article and comments have changed my mind. They are spreading to the two different counties that I travel through ( Pinellas and Pasco). I have been catching them for over 40 years and like having them all over my yard. They eat lots of bugs.
I guess that the orange will be more common now. Very interesting.
Wendy Grant
A. Sagrei spotted today in St. Augustine at the Lighthouse parking lot.
Eden Volkert
I came across this article as I have found many of these in my yard in the last few years. I thought perhaps the color was adapted camouflage from the rust color that well water leaves behind on older Florida home’s exterior walls. The well water tends to stain all surfaces it comes in contact with in a very short time. It tends to be on the lower half of walls where the anoles like to hang out.