Tulane University reports:

Study: Invasive lizards’ tempers flare with the heat

from the pages of Rhody Today:

KINGSTON, R.I. – Dec. 11, 2025 – How do intermittent events like hurricanes impact natural selection? How do animals adapt to challenging weather? A University of Rhode Island professor has set out to track natural selection in the Anolis lizard over time to see how the species has weathered hurricanes in the southeastern United States.

A new paper by Jason Kolbe and colleagues published in the Proceedings of the National Academy of Sciences finds hurricane-induced selection and responses to hurricanes in Anolis lizards. Chair of URI’s Department of Biological Sciences, Kolbe studies how human-mediated global change phenomena drive evolutionary change in the natural world.

If species’ mortality depends on specific traits, then hurricanes — extreme and intermittent in nature — provide a source of episodic natural selection on affected populations. The predicted increase in hurricane activity and strength in the North Atlantic has the potential to alter patterns of selection and evolution for populations, especially in coastal areas and islands.

The paper’s focus brought Kolbe back to the start of his professional research career. He has studied lizards for 25 years and used genetic markers to reconstruct the invasion histories of Anolis lizards introduced to Florida from the Caribbean for his dissertation.

As part of his Ph.D. research, Kolbe studied the ecology and evolution of anole populations on islands in the Bahamas. When Hurricane Sandy hit their study site there in 2012, he decided to use the devastating storm’s impact to compare lizards before and after impact.

The invasion of Anolis sagrei in the southeastern U.S. provided a rare opportunity to put a timestamp on the start of adaptive evolution for populations in this region, Kolbe says. Over 100 hurricanes have hit Florida since the start of the A. sagrei invasion.

Their results affirmed that hurricanes are a source of episodic selection with lasting evolutionary effects on lizard traits connected to weathering storms. Kolbe’s team’s preliminary analysis found lizards with longer limbs survived better during the hurricane and that lizards with longer limbs possessed greater clinging ability, supporting hurricanes as a source of natural selection for lizard populations.

“Our studies of the brown anole in Florida provided an excellent opportunity to test whether hurricane-induced selection could shape the morphology of lizards over the course of their invasion, around 100 years,” he says. “Because we have a good estimate of the time each brown anole population in our study was established and hurricane records go back to 1851, we were able to estimate the number of hurricanes impacting each population and test for an association with traits that increase clinging performance.”

Introduced lizard

The Anolis sagrei was introduced in Florida and Georgia beginning in 1887 in the Florida Keys. It showed up on the peninsula a half-century later. Kolbe’s team reconstructed a chronology of the A. sagrei invasion in Florida and Georgia using dates from published observations and museum specimen records.

Brown anoles were introduced to the U.S. from at least eight geographically and genetically distinct source populations in their native range, mostly from Cuba. These introductions likely occurred accidentally via shipping or intentional introductions (release of pets into the wild).

Kolbe and his colleagues found that brown anole populations experiencing more hurricanes had longer limbs and larger toepads, traits that help them hold on — both in the immediate sense of a single storm and in the long-term as well, in terms of natural selection. Their results confirm hurricanes as a major force shaping variation in Anolis lizards and highlight how the evolutionary trajectories of animal populations will be altered as climate change modifies historical patterns of natural selection, he says.

An evolutionary ecologist, Kolbe studies the evolutionary response of species adapting to rapid environmental shifts and says that biological invasions are useful scenarios to study rapid evolution.

Although there aren’t many good studies on the ecological impacts of this species, its high densities, rapid spread and generalist nature suggest potential impacts on other species, Kolbe says, noting that other species could be studied, as well.

“Lizards are surely not the only species potentially experiencing selection during hurricanes,” says Kolbe. “Our understanding of episodic selection may be enhanced by studies on the evolutionary effects of hurricanes on other species, not only lizards.”

Figure 1. The skin colors of the Anolis carolinensis. (A) Brown; (B) Green.

We’ve long known that some lizards change color for camouflage or communication, but our new research reveals their skin may also act as a dynamic thermal regulator. Our study published in Animals explores how the green anole (Anolis carolinensis) adjusts its skin color and reflectance in response to short-term temperature changes, offering fresh insights into how ectotherms adapt to their environment.

Figure 2. Skin color changes in the same Anolis carolinensis individual under different ambient temperatures. (A) 20 °C; (B) 30 °C; (C) 40 °C; (D) 24-color checkerboard.

Using controlled lab experiments, we exposed lizards to temperatures ranging from 20°C to 40°C against white and brown backgrounds. We tracked changes in skin color, body temperature, and spectral reflectance. Key discoveries include:

1. Brighter at higher temps: As ambient temperature increased, the lizards’ skin became brighter and less chromatic, shifting from dark green to light green.
2. Optimal at 30°C: At this temperature, the lizards’ body temperature closely matched their environment, suggesting a thermal preference.
3. Reflectance shifts: Skin reflectance in both visible and near-infrared light increased with temperature, indicating a role in managing heat absorption.

This study shows that color change in A. carolinensis is not just for hiding or social signaling. It is also a dynamic form of thermoregulation. In cooler conditions, darker skin likely helps absorb more heat. In warmer conditions, lighter, more reflective skin may help prevent overheating. This ability may be especially important for ectotherms (cold-blooded animals) that rely on external sources to manage their body temperature. As climate change reshapes habitats worldwide, understanding these adaptive strategies could be key to conserving ectotherm populations.

Figure 3. Schematic illustration of Anolis carolinensis skin color and body temperature responses to different ambient temperatures.

Reference:

Hu, J.; Xiong, Y.; Liu, R.; Chen, X.; Liang, A.-P. Skin coloration changes and thermoregulation in Anolis carolinensis across different thermal environments. Animals 2026, 16, 203. https://doi.org/10.3390/ani16020203

Figure 1. Sleeping green anoles on leaves (Photographs by Osamu Sakai).

Sleep is one of the most fundamental states for animals, including humans and wildlife. When people travel to unfamiliar places, one of their first concerns is often where they will sleep that night — at least it is for me. Lizards may face a similar challenge.

Like other diurnal Anolis lizard species, green anoles (Anolis carolinensis) are active during the day and rest at night. Sleeping on vegetation is thought to be a common strategy among arboreal anoles, likely reducing the risk of attacks from ground-dwelling predators. But, how do they sleep in the wild when living in an unfamiliar, non-native environment? Which plant species do they use for beds? Do males and females differ in their choices, or do sleeping habits change across life stages? To address these questions, we investigated the night-time microhabitat use of free-ranging green anoles.

Our focal population is A. carolinensis on the Ogasawara Islands, Japan, located about 1,000 km south of Tokyo. This population originated in North America (the Gulf/Atlantic clade) and has been established on these subtropical islands since the 1960s. During night-time surveys, we observed the green anoles perched on leaves with their eyes closed (Fig. 1). They showed no reaction to flashlight illumination and only a weak response, if any, to gentle tactile stimulation. In short, they appeared to be fast asleep!!

Our survey revealed no sexual differences in sleeping sites with respect to perch height (Mean: males = 256.2 cm; females = 261.7 cm) or the plant species used for beds. In contrast, juveniles slept on much lower vegetation (Mean = 103.0 cm) and used different plant species to adults (Fig. 2).

Figure 2. Ontogenetic niche shifts in the sleeping sites of green anoles. Adults and juveniles used different beds in terms of perch height and variety of plant species. The similarity of the plant species was assessed using Pianka’s niche overlap index

We also found that the characteristics of their sleeping sites were influenced by habitat type. Comparisons between natural forests and human-modified areas suggest that local vegetation has a strong influence on the types of leaves that the green anoles sleep on (Fig. 3). In human-modified habitats, the green anoles were frequently found sleeping on two palm species: the Formosa palm and the golden cane palm. However, at natural forest sites where these palms are absent, the green anoles did NOT rely on particular plant species for their beds.

Figure 3. Comparison of the plant species used by adult lizards in (a) natural vegetation (n = 25) and (b) human-modified environment (n = 98). An asterisk (*) after the plant name represents non-native species on the Ogasawara Islands.

Together, our findings provide a natural history note on A. carolinensis. Notably, the green anoles exhibit an ontogenetic niche shift in sleeping site: as they grow, they change both the perch height of the plants and the species they use for sleeping. Is this niche shift also observed in native green anole populations? Does this pattern have adaptive significance? Further research would be valuable in answering these questions.

Finally, we’d like to discuss the implications for invasion biology. On the Ogasawara Islands, the introduced A. carolinensis has caused severe declines in the native insect fauna, including many endemic species. Improving our understanding of the basic natural history of these animals (i.e., sleep ecology) could contribute to more effective management and control. If you’d like to learn more, the full open-access paper is available in Herpetological Conservation and Biology 20(3): 519–527.

Photo by Miriam Lipsky

And who could blame the little green lady–star fruit are delicious!

Miriam Lipsky of Miami explains:

Photo by Miriam Lipsky

“The star fruits (carambola) are indeed from my yard!  I was picking them to give to a friend, since no one in my family really likes them (Editor’s note: hard as that is to believe!), and when I reached for one of them, this cute anole came with it, then refused to leave the basket.”

Miriam also demonstrated her anole photography chops with this lovely backyard brown anole:

Photo by Miriam Lipsky

Red-bellied woodpecker bashing an anole. Photo by Jacques Rifkind.

Brown anole eating a ringneck snake. Photo by Jacques Rifkind

On December 4, 2025 I observed an Anolis (probably A. sagrei) preying upon an adult or subadult ringneck snake (Diadophis punctatus) in a relictual hardwood hammock forest in Miami, Florida, USA. The lizard was in a vertical head-down position on a narrow tree trunk approximately 2 m above ground, and had the snake’s head in its jaws. Unfortunately, as I photographed the encounter, the anole became disturbed and released the snake, so I was unable to confirm whether the lizard would have been successful at killing and consuming the rather substantial prey item. I examined the snake (approximate length 20 cm) and it appeared not to have suffered damage to its head or neck, and was able to crawl normally. Ringneck snakes are terrestrial / fossorial, so presumably the lizard initially attacked the snake on the ground, then subsequently ascended the tree with its prey. Much has been written about the effects of non-native lizard populations on endemic lizard species through competition and predation. This observation suggests that other endemic vertebrate populations may also be affected by these invasives.

On April 21, 2025, in the same hardwood hammock as the above observation (nature trail at A. D. Barnes Park) I watched a red-bellied woodpecker (Melanerpes carolinus) repeatedly beating an adult unidentified Anolis sp. lizard against the trunk of an oak tree approximately 25 m above the ground. Presumably the woodpecker was attempting to pulp the lizard preparatory to dismembering it or consuming it whole. I observed the bird for 10 minutes before it moved out of view. Melanerpes carolinus was previously recorded feeding on an individual of Anolis carolinensis in South Carolina, so this behavior may not be unusual. I have identified A. carolinensis at Barnes Park on several occasions, and it seems to prefer elevated arboreal habitat (a pattern noted in these pages by Ambika Kamath), by contrast with the more commonly encountered A. sagrei which is abundant on the ground or low in bushes and the bases of trees. Because Melanerpes carolinus is most frequently observed in the canopy, it is at least likely that the woodpecker’s prey in this instance was Anolis carolinensis.

A selection of gecko toepads. Top: Gekko gecko by Peter Geissler, left: Pseudothecadactylus australis by Nick Weiger, right: Oedura monilis by Rishab Pillai.

Like in Anolis lizards, the evolution of adhesive toepads in geckos is often seen as a key innovation, allowing these lizards to exploit vertical environments. Gecko toepads are among the most advanced in the animal kingdom – inspiring research in biomimetics and synthetic adhesion for years. Yet, while the physics of sticking has been studied extensively, the ecology and biogeography have not. Most studies focus on morphology and performance in single species or genera, while large-scale ecological analyses have been rare, something that is considered as a major gap in the literature.

That’s where our project began. The idea originated with Assoc. Prof. Dr. Dennis Rödder and Dr. Jendrian Riedel, and the first task was to take a broad-scale look at toepad variation across all geckos. Following the classification system of Russell and Gamble (2019), we categorized every species into one of four types – absent toepads, basal, distal, and fanlike (Fig. 1) – each morphologically distinct while their functional differences are still not fully understood.

Fig. 1: The four toepad categories according to Russel and Gamble (2019). Ventral view of digit IV from representative species: Left pes of Cyrtodactylus khasiensis (absent), right pes of Gekko smithii (basal), left pes of Ebenavia inunguis (distal), and left pes of Uroplatus ebenaui (fanlike). Illustrations modified from Riedel et al. (2024) and Russell and Gamble (2019).

To explore their evolution and geographic distribution, we combined toepad data with open-access resources on species ranges, phylogeny, climate, and habitat types. Following a range of analyses, we decided on some of the most significant results to create the story-line for our publication.

The first valuable contribution is the classification of toepad types across all species (2230 at the time, excluding the limb-reduced pygopodids), data that is now freely available (Fig. 2). In combination with the phylogeny, we confirmed multiple independent gains of toepads and propose a differential pathway of transitions between pad types.

Fig. 2: Species numbers and family distribution across toepad categories. Includes all recent non-limb-reduced Gekkota species as of September 30 2023 (2230 species)(Kukla et al. 2025, Supplement).

Linking this dataset with biogeography and macro-climate, we also examined how different toepad types are distributed across the globe (Fig. 3) and how they relate to climate and habitat use. Interestingly, we found no sharp climatic boundaries between pad types. Instead, global patterns seem to reflect biogeographic history and the environments where geckos diversified. Nevertheless, we see some habitat associations: adhesive pads tend to show up in structurally complex environments like rocky areas, forests, and even urban settings.

Fig. 3: Global species richness maps for each toepad category: (A) absent, (B) basal, (C) distal, (D) fanlike (Kukla et al. 2025).

Overall, our study provides a global overview of toepad diversity and offers a framework for future, finer-scale studies, moving from global biomes to local microhabitats. We show that gecko diversity isn’t just about sticking to surfaces, it’s about how evolution, ecology, and geography stick together to shape the incredible variety of forms we see today.

If you want to read more, check out our open-access paper:

https://doi.org/10.1111/jbi.70087

Sexual dichromatism in anole dewlaps. Anolis insignis above, Anolis transversalis below. Males on left, females on right. Photos appeared in Lizards in an Evolutionary Tree, photographed by Steve Poe (insignis), Arthur Georges (male transversalis) and Alexis Harrison (female transversalis).

Dewlaps—the extensible throat ornaments of anoles—are classically viewed as male secondary sexual traits used in mate attraction and rival assessment. However, many species exhibit fully developed female dewlaps, and in numerous cases, male and female dewlaps differ in coloration (see some great photos and info in past Anole Annals posts here, here, here, and here! The last post actually inspired Dr. Michael Yuan, senior author on this paper, to work on female dewlaps). What drives this sexual dichromatism?

To address this, we assembled a comparative dataset encompassing 292 Anolis species, documenting dewlap colors in both sexes from the literature, field guides, and community science sources including Anole Annals, iNaturalist, and AnoleKey. We classified dewlap colors based on pigment content, focusing on carotenoids and pterins, which produce red, orange, and yellow hues and often serve as condition-dependent signals. Species were classified as dichromatic if males and females did not share color elements. We integrated these data with measures of body size, sexual size dimorphism, and species co-occurrence, mapped onto the anole phylogeny.

Figure 1. Evolutionary patterns of pigment presence in Anolis dewlaps. (A) Ancestral reconstructions showing how carotenoid- and pterin-based coloration evolved in females (left) and males (right). Pie charts indicate the probability of each pigment state at every node, with tip states shown at the ends of the tree. (B) Proportion of species with each pigment type, separated by dewlap dichromatism categories: female-dewlap absent, monochromatic, and dichromatic.

Our analyses indicate that dewlap coloration is highly evolutionarily labile, with frequent gains, losses, and reversals across the phylogeny. Male and female colors are phylogenetically correlated, suggesting some evolutionary constraint. Crucially, sexual dichromatism appears largely driven by female-specific loss of costly pigments, rather than male pigment evolution. This pattern implies that female dewlap coloration evolves under selective pressures distinct from males, rather than merely reflecting a correlated response to male traits.

We also found evidence consistent with signal partitioning: females were less likely to share dewlap colors or costly pigments with sympatric species, particularly in species-rich communities. In contrast, sexual size dimorphism did not predict dichromatism, suggesting that pleiotropic or androgen-mediated constraints are insufficient to explain female color divergence.

In summary, male dewlap coloration remains relatively constrained, likely due to sexual selection, whereas female dewlaps exhibit greater evolutionary flexibility, often losing costly pigments or diverging in hue to reduce signal interference. These results underscore the role of female-driven evolutionary dynamics in shaping ornamental traits and highlight the importance of considering female signaling in studies of sexual dimorphism.

Future work should investigate the behavioral function of female dewlaps and examine UV reflectance, which is currently poorly characterized but perceptible to anoles. Understanding these components will be critical for elucidating the selective pressures driving dewlap evolution and sexual dichromatism.

You can check out the paper here:

Erin P Westeen, Guinevere O U Wogan, Ian J Wang, Michael L Yuan, Loss of pigments in females is associated with sexual dichromatism in an ornamental trait, Evolution, Volume 79, Issue 7, 1 July 2025, Pages 1299–1309, https://doi.org/10.1093/evolut/qpaf075

And a nice digest written about the article here:

Madelynn M Sinclair, Digest: Sexual dimorphism and signs of selection in the dewlaps of female Anolis lizards, Evolution, Volume 79, Issue 8, August 2025, Pages 1690–1691, https://doi.org/10.1093/evolut/qpaf122