All posts by Jonathan Losos

About Jonathan Losos

Professor and Curator of Herpetology at the Museum of Comparative Zoology at Harvard University. 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.

Anoles on Exhibit at the Milwaukee Public Museum



AA stalwart Tony Gamble has provided these two photos from exhibits at the Milwaukee Public Museum. The one above is a knight anole, whereas below, an Archaeopteryx appears to be dining on a green anole, significantly increasing our understanding of the age of the anole radiation.

AA’s other Wisconsin stalward, Greg Mayer, provides the low-down: “The equestris  is from the Rain Forest exhibit. This is a fabulous exhibit based mostly on the Costa Rican rain forest, but including some other tropical/rain forest elements. I take my vert. zool. class there every year, and have used it as part of the pre-trip preparation for Costa Rican field classes. It was funded in part by the NSF, and involved lots of field work–they did latex casts of trees to get the bark right for life size models of them! The Milwaukee Public Museum was much involved in making Costa Rica the center of tropical studies for US-based scientists. The MPM was slightly independent of OTS. They had their own field station, La Tirimbina, which is very nice–I’ve taken students there 2 or 3 times.

Allen Young, the MPM lepidopterist, was the driving force for Milwaukee’s tropical studies. He wrote about his work at Tirimbina in Sarapiqui Chronicle (Smithsonian Institution Press, Wash. DC, 1991). Young first went to Costa Rica in 1968 with OTS, then focused his work at Tirimbina. (Bob Hunter, who owned Tirimbina at the time, also owned part of La Selva, and was involved in getting both places established as field stations.) MPM’s stake in Tirimbina was sold off by then Milwaukee county executive (now governor) Scott Walker, who couldn’t imagine why a natural history museum in Wisconsin could be interested in Costa Rica. Fortunately, another conservation organization bought MPM’s share.

Others were involved in the exhibit creation as well, and though I’ve never asked him, I’ve always thought the Anolis equestris behavior display in the rain forest exhibit may have been a contribution of Bob Henderson. There are several males and females (not sure if they’re freeze-dried, or some kind of model), showing various levels of agonistic display– fans, nuchal crests, open mouth, raised posture– set out on vines/branches. A question I ask vert. zool. students about this display case is how could they tell the lizards are arboreal, even if they were not posed on branches.”

And with regard to the photo below: “The other picture is from the Third Planet exhibit (I’m always tempted to write Third Rock!), from a section of that very good exhibit on the Hell Creek Formation and the end Cretaceous vertebrate extinctions. The MPM has two Archaeopteryx models made up with feathers, and the one in the pic has a dried or model Anolis carolinensis in its mouth, painted a fairly bright green. The other Archaeopteryx model is better done, and that one goes out on loan periodically to other museums (I think I’ve seen it at the Field Museum).


Owls Eat a Lot of Anoles: Data from Dominica

An owl with a green anole.

A recent paper in the Caribbean Journal of Science on the diet of the Lesser Antillean barn owl on Dominica revealed that anoles, specifically the native species A. oculatus, are a very frequent prey item, constituting 193 of the 517 prey items. The authors note that owls are nocturnal and anoles are diurnal and proffer three explanations: 1. the predation occurs at dawn and dusk, when both species are normally active; 2. the anoles are active around lights at night; 3. the owls are catching the anoles while they sleep. We’ve discussed this topic before: owls are known to eat anoles in Cuba and many other places in the neotropics, and there’s the great photo re-posted below (original post here). As far as I’m aware, that’s the only direct observation of an anole being preyed upon by an owl (although a quick search on Google Images will yield many photos like the one at right). We’ve also discussed the parallel  issue of bat predation on anoles in these pages. Clearly, more data are needed!

Global Warming and Lizards: an Article on Manuel Leal’s Trail-Blazing Research

The following appeared in the spring/summer 2016 issue of the University of Missouri publication Illumination.

Consider the Ectotherm: Can “Cold-Blooded” Creatures Survive in a Warming World?

By Melody Kroll

Photos by Manuel Leal

Illumination - Spring 2016

Even as the climate-driven suffering of polar bears tugs at the heartstrings of concerned citizens worldwide, thousands of less-visible species also face disastrous consequences from a warming planet.

These are the “cold-blooded” animals, the millions of amphibians, fish, insects and reptiles, collectively known to scientists as ectotherms. Together these species make up the vast majority of the world’s biodiversity.

Ectotherms are found all over the world, but most make their homes in the tropics, where, obviously, it is warm already. Being used to the heat, one might assume that an extra degree or two wouldn’t make much difference. Wrong. Scientists have recently determined that many tropical ectotherms are already surviving at their upper temperature limits. Even a modest rise may, in fact, be enough to push them into extinction. Consider the plight of tropical lizards, an animal that MU’s Manuel Leal, an evolutionary biologist and associate professor, has spent two decades observing. Studies have predicted that about 6 percent of tropical lizard species will be extinct by the year 2050. A full 20 percent of the world’s lizard species, one study predicts, could be gone by the year 2080.

Consider the plight of tropical lizards, an animal that MU’s Manuel Leal, an evolutionary biologist and associate professor, has spent two decades observing. Studies have predicted that about 6 percent of tropical lizard species will be extinct by the year 2050. A full 20 percent of the world’s lizard species, one study predicts, could be gone by the year 2080.

Like all ectotherms, lizards have an optimal temperature range over which they are able to successfully hunt, eat, move quickly, and reproduce. For most, that active range is between 81 and 84 degrees Fahrenheit.The fear is that, as global average temperatures inch upward, the thermal range available to them will begin to constrict, leaving lizards less and less time to be active.Leal specializes in documenting the behaviors of Anolis, a genus of the Iguanian sub-order of lizards living in habitats throughout the Caribbean, Central and South America. Anolis is an incredibly diverse group of creatures — some 400 species have been documented so far. Anolis lizards are striking in appearance, their bodies radiant in a neon-like glow of greens, yellows and blues.

Because many Anolis species, commonly known as anoles, have evolved over long periods of time in isolated island habitats, their study has become profoundly important in ecological and evolutionary scholarship.

Leal says there is little doubt that anoles are in trouble and that warming is the primary reason. But, despite all the attention they’ve received over the years, he argues that scientists have largely failed to grasp the complicated means by which climate change may be contributing to the lizards’ survival struggles, a failure that could make understanding their vulnerabilities much more difficult.

“We’ve done very well at saying climate change will have an impact on ectotherms, but we don’t know how,” says Leal. “We have painted with a broad brush already; now we have to take the pencil and try to say, ‘Ok, how is this going to happen?’”

With his former graduate student, Alex Gunderson, Leal recently proposed a new conceptual framework aimed at re-thinking how scientists model the effects of climate change on lizards specifically, and ectotherms in general.

The problem, Leal explains, is that previous studies have treated “optimal body temperature” as the primary or only driver of activity.

“Activity time is treated as an on-off switch — a lizard is either active or it isn’t. But, it’s not that way,” says Leal. “We have shown that the effect of temperature on activity is continuous. We have observed lizards engage in all types of activities – eating, mating, fighting — at temperatures outside their optimal body temperatures. Activity is more like a dimmer switch.”

The strength of the new framework, he says, is its organism-centered approach. “The framework nicely illustrates the importance of measuring variables at scales relevant to the species in question or, in other words, of doing natural history work in order to inform climate-change models.”

Leal believes obtaining lizard-level results is critical. “I tell my students that we are the boots on the ground,” he says. “Theoretical predictions need to be tested. In order to be tested, you need somebody that is willing to do the dirty work, somebody that wants to be working at the scale that really represents the organism and to ask, ‘okay, does this really matter?’”

For Leal’s team, this means hours of filming anoles in the field, coupled with even more hours re-watching and transcribing these videos back in the lab. A big chunk of time is also spent catching anoles and collecting morphological data such as body length, weight, and dewlap color (the characteristic fold of skin hanging from anoles’ throats). They also document aspects of the lizards’ subtropical habitats.

This last point is particularly attractive to Leal, because anoles are abundant in Puerto Rico, the place where Leal spent his childhood catching all sorts of critters, anoles among them.

“I just grew up catching everything that moves, from spiders to big things to little things,” says Leal.

His lizard-catching abilities paid off when his biology professor at the University of Puerto Rico one day invited students to help him collect blind snakes. Leal jumped at the chance. “I said, I’ll go! That’s what I like to do. Then I started working with him and eventually did my master’s degree with him.”

Leal started observing anole behavior in earnest while pursuing his master’s degree in Puerto Rico. His thesis involved looking at how anoles signal their physiological condition to lizard-eating snakes. He showed that the number of push-ups a lizard does is correlated with the lizard’s running endurance. “Basically, the lizard is saying, don’t waste your time attacking me because I’ll run away very fast and if you catch me I’ll bite you really hard,” says Leal.

His research provided one of the first demonstrations under natural conditions that prey can honestly advertise their escape abilities, that is, physiological conditions to predators. It has since become a staple study mentioned in the seminal animal behavior textbook.

While a master’s student, Leal met Jonathan B. Losos, a world leader in evolutionary ecology, who was in Puerto Rico on a collecting trip. Leal says, only half joking, that it was his unrivaled lizard-catching ability that impressed Losos to the point that the senior scientist invited him to join his lab and pursue a doctorate at Washington University in St. Louis. “He promised me that as long as I was able to catch more lizards than him, I would be successful at getting a Ph.D.,” Leal says with a laugh. “I had no idea you could make a living studying lizards. Even to this day, I often stop and think how amazing it is that someone pays me for being dirty and catching lizards. That’s cool.”

“That is not why I selected him,” says Losos, now a professor of organismic and evolutionary biology and Curator in Herpetology at Harvard University. “I took Manuel as a student because it was obvious that he really understood the biology of these animals at a very deep level. But, yes, it’s true that Manuel can walk up to a lizard and just catch it with his bare hands. I still don’t know how he does it.”

By way of example, Losos recalls a field trip they made shortly after Leal arrived in St. Louis. “We came across some local fence lizards. Manuel approached one, and it ran away. I said something like, ‘Hah! Manuel. Not so easy as in the tropics, is it?’ Well, he disappeared, and 10 minutes later, he came back holding two lizards in his hand. I have no idea how he does it. I’ve watched him do it. I tried to figure out what he’s doing that I’m not. I don’t know, but he can do it.”

At Washington University, Leal continued his investigation of anole signaling behavior. After earning his doctorate in 2000, he followed up on these behavioral studies with Leo J. Fleishman at Union College in New York. In 2003, he joined the faculty at Vanderbilt University, moving to Duke University three years later. He joined MU’s faculty in 2014. Over the years, his studies have appeared in top scientific journals, includingScience, Nature, Proceedings of the National Academy of Sciences, Proceedings of the Royal Society of London B, The American Naturalist, as well as commercial publications such as the New York Times, The Economist, National Geographic, El Pais and Der Spiegel.

Leal’s most recent work seeks to advance scientists’ understanding of how temperature affects anoles’ behaviors. Along with Gunderson, he has proposed that temperature differentially affects four elements of activity that the researchers define as thresholds, probabilities, modes and vigor.

Thresholds, they explain, are the temperatures below and above which animals are inactive. Probability involves evaluating whether an animal will engage in activity when its body temperature is between the lower and upper temperature ranges. Mode is about activity, for example feeding, mating, fighting. Mode of activity is important because different modes have their own temperature-dependent probabilities. Finally, the researchers seek to determine the vigor with which an animal engages in an activity.

“Each of these components has been studied to some extent previously, but it was always only one of them,” says Gunderson, who is currently completing his postdoctoral work at San Francisco State University’s Romberg Tiburon Center. “In order to get a comprehensive understanding of how temperature is going to influence activity, you really need to know how all of these components are interacting simultaneously.”

The authors have applied their framework to document the consequences of climate warming on Anolis cristatellus, a tree-dwelling lizard found in both dry and wet habitats on the island of Puerto Rico. In the case of A. cristatellus, they sought to learn how the lizards’ overall health affected crucial behavioral characteristics.

Their findings showed that behaviors such as eating and mating are extremely sensitive to thermal change, especially compared to sprinting speed, the physiological trait typically used to measure climate-change effects.

“For example, our analyses show that the physiological performance of A. cristatellus in dry habitats will decrease by about 25 percent under future warming, but their activity budgets will decrease by 50 percent. Furthermore, the habitat will become much less suitable for reproductive behaviors, which are, of course, critically important for the viability of populations,” says Leal.

In other words, adds Gunderson, physiological traits alone may not be the best way to estimate the consequences of climate change. What we really need, he says, is to integrate both the physiological and behavioral.

“Even though organisms might have relatively high physiological health, if they’re not eating or reproducing then there are going to be big population consequences,” Gunderson says.

“If anything,” Leal adds, “what we have done is taken all these data and put them at the scale of the lizard and asked, can we predict what the lizard will do when we have the interactions of the temperature of the environment, body temperature, and sprint speed, which is basically the curve on which behaviors will happen.”

“Previously, we could say, yes, they can live in place A or place B and that is true. Now, we can say, when they are in place A, they will not be able to mate as often as they would if they were in Place B or they will not be able to defend their territory as often if they were in this environment. So it’s more at the scale of the individual.”

Harvard’s Losos calls Leal’s conceptual framework “a major step forward” in our understanding of how global warming will affect all ectothermic animals.

“Previous work has recognized the importance of changing temperatures but hasn’t been very sophisticated in trying to evaluate how global warming might affect the biology of the species,” he says. “What Gunderson and Leal do is take a much more in-depth examination of the biology of the species and how temperature really affects what they do and when they do it or how much they do it to present a framework to understand whether species will be able to cope with changing climates.”

Such insights don’t come by accident, Losos says. They happen because scientists like Leal and his graduate students spend a “huge amount of time out in nature actually studying animals and what they do. There is simply no substitute for understanding the biology of animals in their natural environment. Nonetheless it takes a huge amount of effort to collect those sorts of data: time, money, and being out in uncomfortable situations often. Most scientists don’t do that. What Manuel has shown is that this sort of data, what we call natural history, is critical in understanding how animals interact with their environment, and how, as the environment changes, animals will be able to respond. What is really unusual about their approach is that they are not sitting in a lab and making a bunch of assumptions and running data through computers. They’re out in nature getting the data we really need to have.”

The hope, Gunderson says, is that these “natural history” data, coupled with the revised conceptual framework he and Leal developed, can help scientists develop strategies to better predict and, one day perhaps, mitigate the effects of climate change on these vulnerable animals.

“Everything we talk about in this paper is relatable to other cold-blooded animals. That was something we really wanted, to make sure that what we were presenting, even though we were using lizards as a model, was applicable to a wide range of animals.” The types of animals, Leal would hasten to add, that can best be understood by “thinking outside the lab.”

“While laboratory studies of the effect of temperature on the physiology and behavior have provided significant insights into thermal ecology of ectotherms,” says Leal, “the time is ripe to take this knowledge outside the lab to further develop climate-change models.”

Continue reading Global Warming and Lizards: an Article on Manuel Leal’s Trail-Blazing Research

Two Reviews of The Anoles of Honduras

A year ago, McCranie and Kohler published The Anoles of Honduras: Systematics, Distribution, and Conservation (available on Amazon for under twenty bucks and downloadable for free on the Museum of Comparative Zoology website).

In case you missed them, we thought we’d provide copies of some recent reviews of the book–in the last year, two favorable book reviews have appeared by Levi Gray in Herpetological Review and by Steve Poe in Quarterly Review of Biology.

Anolis sagrei on Grenada with a Broken Dewlap

Anolis sagrei

Anolis sagrei

From time to time, people find anoles with broken dewlaps. Here’s an extreme example, found by Bob Powell and Rich Sajdak on the island of Grenada. Years ago, Richard Tokarz reported a lab study that showed that males with non-functional dewlaps mated as frequently as intact males, and a follow-up study with Ann Paterson and Steve McMann showed no difference in the field between males with and without working dewlaps. Makes you wonder what the dewlap is needed for.

Bob points out that brown anoles have spread widely in disturbed lowland habitats since first discovered on Grenada in 2002, when they were restricted to intensely disturbed urban habitats and decorative plantings in a few resorts.

Bob Trivers Publishes His Memoirs, Lizards and All

All evolutionary biologists are familiar with Robert Trivers, but many do not know that some of his most important work was conducted on Anolis lizards. This work–as well as the rest of Trivers’ life–is featured in his just-published memoirs, Wild Life: Adventures of an Evolutionary Biologist. I had the good fortune to review the book for Current Biology. You can read my review, but the short story is: a fascinating book about one of the great figures–and characters–of modern evolutionary biology. And in case you’re wondering, it was the publishers who put a collared lizard, instead of an anole, on the cover. Available on Amazon for $12.99!

Nectarivory by and Predation upon Anolis occultus: Natural History Data at Last!


Remarkably little is known about the natural history of the Puerto Rican twig anole, Anolis occultus, except where it sleeps. The reason is simple: thepredation animal is small, moves slowly, is highly cryptic and probably spends a lot of its time amidst the twigs high in the canopy. As a result, there have been reports of only a handful of animals located while they are active.

In a just published paper, Ríos-López and colleagues report two new observations of these charming little lizards, one of nectarivory (above) and the other, sadly, of predation by a kingbird (right). In addition, the paper presents a comprehensive review of what we know about this species and its conservation prospects.


What Is a Dewlap and How Many Times Have Dewlaps Evolved?

Not a dewlap? Photo by Morley Read.

In a recent paper, Hagman and Ord discussed how dewlaps have evolved multiple times, often with different underlying anatomy. This is an excellent paper, but I was intrigued that Polychrus, sometimes considered the sister taxon to anoles, in part because of its apparently anole-like dewlap (see above), was not considered to have a dewlap.

I wrote Terry Ord, asking “I didn’t understand one thing. You seem to say there is no evidence for extendible dewlaps in several species of Polychrus, but a quick Google reveals plenty of images of these species with dewlaps extended. I take your point in the previous sentence that actual observations of the dewlap being used are rare, but did you really mean to say that they don’t exist at all?”

Terry responded: “What I found when attempting the first paper of this series (Ord et al. 2015, Journal of Evolutionary Biology) is that relying on photos alone is really problematic for identifying a moveable dewlap (a.k.a., a dewlap like anoles or Draco or Sitana).

For example, if you google Sceloporus — who definitely don’t have dewlaps — you’ll find photos where species do appear to have something like a small dewlap. In fact, I found an image of what was clearly a Sceloporus that looked to have an engorged throat that was remarkably similar to your Polychrus photo… All the google images I’ve found so far that are obviously Polychrus (and not anoles) could quite easily be engorged throats akin to Sceloporus and other non-dewlaped iguanids/agamids.

But the clincher for me is that all the hyoids we’ve looked at so far for both Sceloporus and multiple species of Polychrus (and other non-dewlaped iguanids/agamids) all look very similar (e.g., see Fig 5a in the JEB paper and supplementary info). The point being, the mechanics of the hyoid simply isn’t functional in the capacity of extending a dewlap like in anoles and others.

Of course, while the mechanics of the hyoid in extending the dewlap in anoles is well described, how Draco do it and some other genera is unclear. I’m hoping someone will look into detail on the biomechanics of the dewlap extension in non-anole groups because it can clearly be very different to anoles — e.g., the attachment points for key muscles for the anole dewlap are absent in Draco, so they’re sticking that dewlap out using a very different mechanism. Regardless, there are still key signs in the hyoid that point to a moveable dewlap in Draco (and other genera) that are not present in Polychrus.

Proof of a Polychrus dewlap would have to be a video of a Polychrus extending the dewlap because videos of Sceloporus quickly reveal that its an engorging (“puffing”) of the throat, so direct observation is a solid alternative to looking at the hyoid.

The taxonomy of “Polychrus” is potentially sketchy and not all species really are of that genus. Which means I also wouldn’t be surprised to see a species that has been classified Polychrus, but really isn’t related to all the Polychrus species we’ve examined the hyoids of, actually having a convincing moveable dewlap.

But at the moment, Polychrus = a moveable dewlap, all the evidence says otherwise. I also wonder whether the historical association of Polychrus as basal to anoles resulted in reaffirming wishful thinking field observations into the current myth.”

Terry’s next email made the distinction clear (as well as his unwarranted agama-philia): “If your notion of a dewlap is a prominent ornament that is dynamic in some sense (becomes extended through puffing out the hyoid in general or pushing out the CII in particular), then there are many many examples in agamids, and a handful in iguanids. I would definitely include Sceloporus, too.

If your notion of a dewlap is more specific to something that is part of a complex behaviojral display and involves rapid extension of a structure that is complex in temporal and amplitude characteristics, then it’s basically anoles, Sitana/Otocryptis, Draco and possibly one or two other agamids.

Agamids still clinch the diversity stacks in all regards – ha!”

Also not a dewlap.

New Research on How Tail Regeneration Works

Tail successfully regenerated.

Recent years have seen renewed interest in the mechanisms underlying tail regeneration in reptiles, and anoles have been a major study organism. The latest word comes from Thomas Lozito and Rocky Tuan who have just published a paper, “Lizard tail skeletal regeneration combines aspects of fracture healing and blastema-based regeneration” in Development.


Lizards are amniotes with the remarkable ability to regenerate amputated tails. The early regenerated lizard tail forms a blastema, and the regenerated skeleton consists of a cartilage tube (CT) surrounding the regenerated spinal cord. The proximal CT undergoes hypertrophy and ossifies, while the distal CT resists ossification for the lifetime of the lizard. We hypothesize that differences in cell sources and signaling account for divergent cartilage development between proximal and distal CT regions. Exogenous spinal cord implants induced ectopic CT formation in lizard (Anolis carolinensis) blastemas. Regenerated spinal cords expressed Shh, and cyclopamine inhibited CT induction. Blastemas containing vertebrae with intact spinal cords formed CTs with proximal hypertrophic regions and distal non-hypertrophic regions, while removal of spinal cords resulted in formation of proximal CT areas only. In fate mapping studies, FITC-labelled vertebra periosteal cells were detected in proximal, but not distal, CT areas. Conversely, FITC-labelled blastema cells were restricted to distal CT regions. Proximal cartilage formation was inhibited by removal of periosteum and could be recapitulated in vitro by periosteal cells treated with Ihh and BMP-2. These findings suggest that proximal CTs are directly derived from vertebra periosteal cells in response to BMP and Ihh signaling, while distal CTs form from blastema cells in response to Shh signals from regenerated spinal cords. Thus, lizard tail proximal CTs develop independently from tail blastemas, resembling cartilage calluses formed during fracture repair, while distal CTs are derived from the blastemas similar to regenerated salamander tails.

Risque Anole Bachelorette Party Cake

cakeWe’ve seen anole wedding cakes and thesis defense cakes, but here’s a new one. Anole research veteran Natalie Jacewicz reports:

For my bachelorette party, my bridesmaids went to an erotic bakery (quite the business niche) in Boston and brought the shop pictures of Anolis lizards. The bakery evidently usually deals in, er, human encounters, so only had skin-toned frosting, and the store clerks weren’t sure if they could do anything lizard themed. But the shop owner evidently got really into the project, did a lot of independent anole research, and produced the cake below. Yes, that is a bridal veil on the yellow one.

Musings on the Lizards, Snakes and Other Herps of Florida

Photo by Janson Jones

Janson Jones is at it again. Actually, he’s been at it for a year, but somehow that slipped below our radar. The former purveyor of Dust Tracks on the Web has a new venue, florida wildlife, ecology and more.

Like it’s predecessor, phosTracks is full of keen natural history, engagingly presented and complemented by gorgeous photography. And better yet, anoles are one of Jones’ two favorite animals, neck-and-neck (hard as it may be to believe) with watersnakes.

Check out some of Jones’ recent musings on:

curly-tailed lizards:

Photo by Janson Jones

red-headed agamas:

Photo by Janson Jones

Anolis cristatellus:

Photo by Janson Jones

and more! Stay on these pages for some of his giant anole goodness coming up soon!

Brown Anoles Invade New Orleans: What Will Happen to the Greens?

Just in time for the American Society of Ichthyologists and Herpetologists meeting in New Orleans next week. From the New Orleans Advocate:

It flashed across the walkway like a lightning bolt, so fast that Bob Thomas had to do a double take. In that split second six months ago, he knew they had finally arrived.

“I’d been waiting for them to arrive in my neighborhood in Metairie. What I saw moved too fast for what we’re used to around here,” said Thomas, a herpetologist who taught at Loyola University and served as the founding director of the Louisiana Nature Center.

“It could only be one thing: a brown anole, Anolis sagrei.”

You’ve seen them — the speckled brown lizards that come out of nowhere and streak across the sidewalks. They travel in hordes — tiny, large and everything in between. Careful! You’re liable to step on them if you don’t pay attention.

Thomas’ neighborhood is far from being the first to experience an invasion of brown lizards. But where did they come from? Why are they so plentiful?

“Brown anoles are an invasive species, not native to the United States,” said David Heckard, curator of reptiles and amphibians at the Audubon Institute. “They are natives to Cuba and the Bahamas and first appeared in the U.S. in Florida. From Florida, they’ve been slowly expanding their range across the Gulf Coast. They’re aggressive and competitive and have even been spotted in Taiwan. They hitch rides on plants and are spread inadvertently by plant nurseries.”

The brown anole looks a lot different than the sleek green lizards we grew up with here in New Orleans (Anolis carolinensis). Generally, A. sagrei has a more compact physique and a shorter skull. A prominent hump appears where muscles attach at the back of the skull. When the brown anole extends its orange and red dewlap (the skin flap below its chin), it looks ferocious, indeed.

By contrast, the green anole looks far friendlier, even when its rosy-hued dewlap is extended. Native to the southeastern parts of the United States (although DNA studies suggest they originated in Cuba and came here a couple of million years ago), green anoles range as far north as North Carolina and as far west as Austin, Texas. They have delicately shaped heads and long, lean bodies. They were once plentiful in New Orleans, but sightings are becoming rare.

So, are the brown anoles killing off the green anoles, fighting over territory and winning? Consuming the green anole’s food supply?

“The theory is that the brown anoles are displacing the green anoles but not necessarily replacing them,” Heckard explained. “It’s believed that green anoles are more arboreal than brown anoles, which are more terrestrial. So, green anoles are being pushed to higher elevations — up into trees and the like. It may seem as though there are fewer of them, but they’re present — you just can’t see them hiding in the leaves and up in trees.”

Simon Lailvaux, a professor in UNO’s department of biological sciences, has studied anoles since working on his doctorate and supports the displacement theory.

“In the Caribbean, where there are dozens of species of lizards, they have learned to partition the habitat and have evolved to live in a specific part of it,” Lailvaux explained. “Green anoles there are trunk/crown inhabitants, whereas brown anoles are trunk/ground inhabitants. Over the millions of years that green anoles have been in the United States, they evolved to be able to occupy the ground because they didn’t have any competition for it. So, the relatively recent invasion of brown anoles has simply forced them back up into trees where they originally lived.”

Are we sure about that? Is anybody counting?

“How can you count green lizards way up on tree trunks and in the leaves at the crowns of trees?” answered Lailvaux. “You can’t.”

According to all three scientists, both types of anoles eat the same things: insects and other invertebrates. There are plenty of those to go around here, so it’s improbable that the green anole’s food supply is in jeopardy. Luckily for the green anoles, they may have a significant competitive advantage over the invaders.

“Brown anoles are cold sensitive and can survive only in a limited temperature range. That means the population of brown anoles crashes when we get a hard freeze, and it takes forever for their numbers to recover,” Lailvaux said. “The green anole, on the other hand, has evolved to be able to withstand lower temperatures, so they won’t be bothered by a freeze. We’re seeing, though, that it is taking less and less time after a freeze for the brown anoles to recover, which means they’re already beginning to adapt.”

The mild winters of the past few years may account for the explosion in the visibility of the brown anoles. But if A. carolinensis is being replaced (not merely vertically displaced) by A. sagrei, it would be a case of a native species dying out because an invasive species outcompetes it. Should we be looking into how to reverse that trend?

“The green anole may be a nostalgic favorite, but we don’t know yet what impact the proliferation of the brown anole will have on it or on other species. The sense is, however, that it won’t be wonderful,” Thomas said.

We know too well what an invasive species can do: Witness the nutria. By consuming the marshes, the animals not only reduced storm surge protection for our area but caused the demise of other species that called the marshes home, Thomas pointed out. Without further study, there’s no way to predict if the success of the brown anole could be similarly dire for the green anole and for biodiversity.