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Green anoles (Anolis carolinensis), also described as the American chameleon, can change between brown and green coloration at will in a process known as physiological color change. Deciphering the adaptive purpose of this ability has captured scientists for over a century, with three major hypotheses dominating research: camouflage, social signaling, and thermoregulation. Social signaling is the most well-supported explanation in recent literature, while camouflage has lacked evidence. However, thermoregulation has remained contentious, as older studies show strong support for the hypothesis while newer studies show weak or no support. Seeing this disconnect, my coauthors (Robert Guralnick, Coleman Sheehy III, and Jacob Idec) and I attempted to evaluate these three hypotheses through a novel method to provide fresh insights into what drives color change in Anolis carolinensis.

Diagram of the computer vision pipeline

In our recent paper, we harness over 10,000 images from iNaturalist and recent advances in computer vision technology to evaluate the support for each of these hypotheses at a large scale. To determine the color of the anole in each observation, we utilized Meta’s new SegmentAnything Model (SAM) to generate segments of the anole in the image, filtered out poor segments, and then used a simple equation to determine whether the anole was presenting green or brown. Then, by using the metadata attached to community science posts, we were able to retrieve the exact date-time and estimate the temperature at the moment of image capture. Using these data, we found a strong correlation between the proportion of anoles observed as brown and lower temperatures. Interestingly, during the summer breeding season, this correlation completely disappeared. Additionally, the difference in proportions of green and brown presentation throughout the year was strongly linked to latitude. These observations combined provide evidence for both the thermoregulatory hypothesis and the social signaling hypothesis, which suggests multiple adaptive drivers of color change in this species.

Although big-data observational studies such as this are insufficient to prove the ultimate cause of physiological color change in green anoles, we believe that this paper can serve as a guide for future research that takes time of year and location into account when testing these hypotheses. Furthermore, this research shows that community science has immense potential in big-data studies, especially when working in tandem with artificial intelligence systems such as computer vision. Therefore, we must thank all of the spectacular citizen scientists on iNaturalist to thank for this amazing project, and we hope that more scientists take advantage of the breadth of data available from our communities.

If you would like to read the entirety of this paper, it can be read for free at this link: https://rdcu.be/eMrgE

Rebreathing Semi-aquatic Anoles: Just a Scuba Tank… or Something More?

By Lindsey Swierk

On October 15, 2025

In All Posts

Over the past several years, semi-aquatic anoles experienced a bit of viral fame for “scuba diving,” a nickname for their ability to rebreathe a bubble of air over their nostrils while diving underwater. Rebreathing allows anoles to remain underwater for a long time and theoretically escape their terrestrial or aerial predators. My collaborators and I have clocked rebreathing semi-aquatic anole dive times of about 20 minutes, though — who knows – it may even be longer! Chris Boccia and Luke Mahler led a collaborative study a few years ago in which we found that these rebreathed bubbles do decrease in oxygen over a dive, which tipped us off that anoles are actually using bubbles in respiration.

Water anole (Anolis aquaticus) rebreathing a bubble of air. Photo by: L. Swierk

But aside from being just a mind-boggling behavior to watch and a nerdy party factoid, the existence and function of rebreathing immediately hatches dozens of ecological, evolutionary, and physiological questions. One of the most fun and puzzling of these is: how are anoles actually able to stay underwater so long just by using the oxygen in their old, exhaled breath? We were puzzled by this too since, despite the relatively low oxygen demand expected of a lizard in cool stream water, we already knew that there was something funny going on with oxygen availability in these rebreathed bubbles toward the ends of dives. Instead of decreasing linearly like you would expect, the oxygen decrease in bubbles actually slowed over time. Could this mean that – when oxygen was needed most — the rebreathed bubbles were picking up oxygen from the water surrounding them?

That air-breathing animals extract oxygen from water via bubbles is certainly not a new idea. There is solid evidence of so-called “physical gills” in many air-breathing invertebrate species, including beetles, water bugs, spiders, and even scorpions! These species maintain bubbles on or near their bodies, and they get enough oxygen from the diffusion of dissolved oxygen from the water into their air bubbles to respire and remain underwater for long durations (sometimes indefinitely!).

Given the relatively small size of these invertebrates, versus the larger sizes and greater oxygen demands of semi-aquatic anoles, we thought it extremely unlikely anoles would be able to entirely rely on physical gills for indefinite respiration. But… perhaps oxygen diffusing into their bubbles could at least extend their dives? Even only a small increase in dive time could offer a benefit when it comes to predator avoidance.

My then-PhD student, Dr. Alexandra Martin, an NSF REU student, Diane Cordero-De La Cruz, and I decided to design an experiment to begin to test this idea, using our lab’s favorite (don’t tell!) semi-aquatic anole: Anolis aquaticus. In controlled lab conditions, we altered the levels of dissolved oxygen in tanks, predicting that if lizards were able to use their bubbles as physical gills then they would be able to stay submerged longest in the most highly oxygenated tanks. We were surprised and intrigued to find exactly this – A. aquaticus dive durations increased significantly when dissolved oxygen in the water was highest, and dives were shortest when dissolved oxygen was lowest. Anoles also rebreathed fewer bubbles as dissolved oxygen increased. These patterns suggest that rebreathing bubbles may be more than just an oxygen “tank”… bubbles may also be functioning as a physical gill, replenishing the air bubble with oxygen from the surrounding water. Use of a physical gill would be a first for any known air-breathing vertebrate.

Dive duration and numbers of rebreathed bubbles (shown as estimated marginal means; EMM) of water anoles diving in low, medium, and high dissolved oxygen (DO) tanks. Figure from Martin et al. 2025, Journal of Experimental Biology

There are many next steps to confirm the mechanism and adaptive function of our results, one of which is to directly measure oxygen diffusion into the bubble. But we are fascinated by the story that these findings are beginning to tell: that anoles may be pushing the envelope of vertebrate respiration in ways we’re only beginning to appreciate. As always, anoles find a way.

You can read more about our findings in our new paper in the Journal of Experimental Biology: “High dissolved oxygen extends dive duration and suggests physical gill use in a vertebrate.”

Water anole (Anolis aquaticus) on a rock

Water anole perched on a streamside boulder. Photo by L. Swierk

Brown Anoles as a Backyard Ecosystem Menace

By Jonathan Losos

On October 12, 2025

In All Posts

photo from San Angelo Standard-Times

Galveston reader A.J. Watkins writes in:

I am in Galveston Texas, and I am literally in tears. Being a Port city, we have been invaded by the Cuban anoles that have obviously come in off the shipping boats. All I can say is they have caused complete devastation to SO MANY native species here on the island. Where once I had assassin bugs calore in my yard, as I never use pesticides, I also hardly ever had any issues with plant pest bugs, as the assassin bugs ( I called them my garden army) would take care of the aphids, white flies, mealy bugs, etc.

Now, since the invasion ( and I do mean INVASION) of the Cuban brown anoles, they have decimated the assassin bug population. I haven’t seen a single assassin bug for at least 3 years now. They also eat all the Pipevine Swallowtail Caterpillars, the Monarch caterpillars, and the Giant Swallowtail Caterpillars. They do kill and eat all the baby green anoles, the green anole eggs, and will outcompetes and fight with the larger Green anole males. As of this year, my back yard is over run with Cuban anoles, and I am talking HUNDREDS of them.

I try to keep the Cuban anoles away from my front porch area, as I did have 3 green anoles that hung out on the plants on my front porch. That was earlier this summer. Since then, I had one baby green anole hatch out, but then disappeared ( she was SO TINY) I am assuming she got eaten by a Cuban anole. In the past couple of weeks, the one large green anole male I had, has disappeared, as well as the adult female I had hanging out up here on my porch too.

Second Invasion of Africa by the Festive Anole

By Jonathan Losos

On October 6, 2025

In All Posts

Yes, the brown (aka, festive) anole is at it again. Now it’s turned up on the island of Bioko in the Gulf of Guinea. As Malanza et al. report in Herpetological Notes, this is the second introduction of the species to Africa, the first occurring in Angola.

A Yellow Green Anole

By Jonathan Losos

On September 30, 2025

In All Posts

Yellow Anolis carolinensis. Photo by Gary Dick.

Reader Gary Dick tells us: I encountered the hatchling pictured about 10 years ago on my patio. Part of a small population in my specific area. Best I can tell, it was achromic Green anole. What do you think?

A little additional info about this lizard: it’s from a population I established in my yard about 25 years ago north of Dallas Texas over a period of ten or so years. Individuals (mostly adult) from southeast Louisiana, northwest Louisiana, and northeastern Texas, plus the very occasional one I encountered in this general area. My guess is the population has experienced founder colony effects from the multiple but low number introductions, leading to the genetic magnification of a few recessive traits. From my limited knowledge of genetics and some interesting AI discussions, I’m leaning toward a triple recessive condition that includes amelanistic, xanthic, and iridiophore-limited traits ( hence my probable inaccurate use of the term “achromatic”). Or, a single or double recessive condition maybe accounts for all three traits. The most interesting thing, perhaps, is that I observed this in the individual photographed as well as two other individuals with the same traits over a six week period.

From the same population, I am now seeing a few individuals with “patchy” coloration…splotches of dull when the animal is brown. The same areas appear brownish when the animal is green.

Photo by Gary Dick.

photo by Gary Dick

Can Anoles Regenerate Their Skin?

By Jonathan Losos

On September 28, 2025

In All Posts

Brown anole with green new tissue growing on right side of torso around evident bite mark

Photo by Christopher Brown in Field Notes.

Christopher Brown on his blog Field Notes writes:

“We may never acquire the gift evidenced by this anole I saw on our retaining wall last weekend: the ability to regenerate large portions of one’s own body after an accident or an encounter with a predator.

I was grilling dinner when I saw it, and had to raise my glass in admiration. Long live the new flesh. May your descendants grow large, and lord over the rewilded ruins we leave behind.”

I’ve seen anoles like this before. Is skin regeneration the explanation?

More on Anole Eye Spots

By Jonathan Losos

On September 4, 2025

In All Posts

Photo by Seth Whaland.

Some green anoles sometimes temporarily develop a black spot behind their eyes. We had a great post on why this happens in 2011. Spoiler: it’s a sign of stress.

Photo by Seth Whaland

Reader Seth Whaland has provided interesting observations: In August of this year, I was on the Butler Hike & Bike Trail along Lady Bird Lake in Austin, TX. I was walking along the trail with a new point-and-shoot 35mm camera when I spotted two anoles. I watched them for a while and knew I wouldn’t be able to get close enough with my camera to get a decent photo without disturbing them, so I used my phone. The two lizards circled each other, both extending their dewlaps, doing “push ups” and opening their mouths (biting?) until one of them pushed the other one off of the branch. It happened quickly so I’m not totally clear on what it did to cause the other to fall. I believe it was in a live oak tree.

New Orleans’ Brown Anoles Can Tolerate Extraordinary Amounts of Lead in Their Blood

By Jonathan Losos

On August 23, 2025

In All Posts

Tulane University reports:

Lead-resistant lizards in New Orleans could hold clues to combating lead poisoning

August 20, 2025 9:00 AM

Stacey Plaisance splaisance@tulane.edu

New research from Tulane University found that brown anole lizards in New Orleans carry the highest blood-lead levels ever recorded in a vertebrate — amounts that would be lethal to most other animals — yet they appear unaffected.

The study, published this month in Environmental Research, found that the lizards’ blood lead levels exceeded all previously reported values for fish, amphibians, birds, reptiles and mammals.

“What’s astonishing is that these lizards aren’t just surviving, they’re thriving with lead burden that would be catastrophic for most other animals,” said study author Alex Gunderson, assistant professor of ecology and evolutionary biology in Tulane’s School of Science and Engineering.

“What’s astonishing is that these lizards aren’t just surviving, they’re thriving with lead burden that would be catastrophic for most other animals.”

Alex Gunderson, School of Science and Engineering

Lead is a pervasive environmental pollutant with severe health impacts, especially in urban settings. The research underscores the lingering legacy of lead contamination in New Orleans and the complex ways organisms adapt — or fail to adapt — to polluted environments.

The brown anoles are an invasive species originally from the Caribbean. They’ve been in New Orleans since at least the 1990s, but their population has increased over the last 20 years, and they are now more common than the green anole, which is a native species.

PhD student Annelise Blanchette and Gunderson led the study and discovered that the lizards could withstand lead levels about 10 times higher than the already extreme concentrations found in the field before showing any decline in performance.

Tests measured traits such as balance, sprint speed and endurance — abilities commonly impaired by lead exposure.

“These animals are performing at full capacity despite record-setting lead levels, making them one of the most, if not the most, lead-tolerant animals known to science,” Blanchette said.

Transcriptomic analyses of the animals’ brain and liver tissue showed only minor effects from lead exposure, although several altered genes were linked to metal ion regulation and oxygen transport.

The findings raise new questions about how the reptiles survive such toxic exposure and whether those mechanisms could someday inform treatments for humans and other wildlife.

“We need to reevaluate what we know about toxicity thresholds in vertebrates,” Gunderson said. “If we can figure out what’s protecting them, we might uncover strategies that could help mitigate heavy metal poisoning in people and other species.”

While this study does not suggest humans can develop the same resistance as these lizards, the discovery of such extreme lead levels in a vertebrate highlights the persistent presence of lead in the environment and the urgent need to reduce exposure in people, particularly in communities where contamination remains widespread.

Article in Smithsonian Magazine

Non-native Herps Still Increasing in the Most Heavily Invaded Herp Community in the World.

By Stephanie Clements

On July 6, 2025

In All Posts, New Research

A large green lizard in the foreground perched on a tree, with an open grassy area behind and a natural area in the distance.

Anolis equestris during one of our Miami surveys

There truly is never a dull moment in South Florida, especially for those of us who love herps. South Florida is a herper’s paradise with at least 63 exotic herps recorded in the state in addition to some unique and endemic native species. In fact, South Florida is the global hotspot for non-native herps, and the world’s most invaded continental ecoregion. While almost all the herps we see while walking around Miami are non-native, we are also almost always in heavily human-modified habitat. This led us to wonder if we would see more native species if we were at sites where native habitat was preserved. Back in 2017, we set out to answer this question, comparing herp communities between 15 parks with natural habitats and 15 parks with primarily anthropogenic features (think playgrounds, baseball fields, and dog parks). Spoiler alert: Non-native species dominated the herp communities in all of the parks, natural and anthropogenic alike. Non-natives made up a whopping 90.6% of all individuals we identified. Perhaps unsurprisingly for those who have grown accustomed to the small lizards scurrying along their sidewalks and fences, 86% of everything we saw was from the genus Anolis.

Fast forward to 5 years later. It’s 2022 and all of us herpetologists in Miami are constantly being asked by anyone who learns of our lizard expertise, “What’s this big new lizard I keep seeing?! It’s got an orange head and tail and a blue body,” or “I keep seeing these lizards with curly tails hanging out around my house – what are they?” These two large predatory lizards, agamas and curlytails, are clearly spreading around the county, to the point where even non-lizard-people are taking note. As we look around, we can’t help but wonder if there could be a change in the composition of our already very exotic herp community in Miami in just the 5 years that have passed since our former study. So, we set out to answer that question.

Several months later we’d completed the same surveys at the same 30 parks, with a fantastic team of researchers, exactly five years after our first study. What did we find? Well, despite both the incredibly short time span and South Florida already being the most invaded herpetofauna community in the world, we found that non-native herps were still increasing in both richness and abundance, in amounts that were measurable in just a 5-year period! Non-native herp abundance increased significantly by 32.7%, while native abundance did not change significantly (only a 6% increase). This time around, 92.3% of our observations were non-native herps. Once again, most of our observed individuals were anoles (82%), and brown anoles and green anoles were our most commonly observed species, both being found at 97% of all sites surveyed. It is worth mentioning, however, that even the 7.7% of observations that were classified as “native” have a caveat: Most of these observations were Anolis carolinensis. As readers of Anole Annals likely know, there is now evidence that most Anolis carolinensis in Miami are hybrids with the non-native Anolis porcatus. If these are reclassified as non-native, our native count is down to just ~1%.

Figure caption: Bar graphs showing the difference in mean (a) abundance and (b) richness (±95% Confidence intervals) by year. Total abundance (p = 0.043) and richness (p = 0.001), as well as non-native abundance (p = 0.032) and richness (p = 0.0012), increased significantly from 2017 to 2022, whereas native abundance and richness did not (p > 0.4).

While Anolis spp. make up most of our observations, it was really the agamas and curlytails that stole the show this time around.