Anole Annals

Now that I have reviewed the diversity of South American anoles north and south of the Andes, I will discuss conservation issues in this region. I will start by identifying some of the major threats to anoles, attempt to identify what makes particular anole species vulnerable, and conclude with discussion of the path forward for work with these species.

Threats

As pointed out in the review of introduced species, the general lack of invasive species means that invasives are of relatively low concern at this time, though this could change if more introduced species become invasive. Rather, the major threats to anoles in South America are probably habitat loss and climate change.

Given that one can fly for several hours and seemingly pass over nothing but intact tracts of Amazonian forest, habitat loss seems like it should be a low concern. However, recall in previous entries in this miniseries I pointed out that many species of anoles are range restricted to just a few areas geographically. Hence, the loss of habitat in just the wrong place could wipe out an entire species in one clearcut or fire event. This is especially true for species close to or adjacent to areas with large human populations, such as southeastern Brazil or around other urban centers. For example, species occurring in the Atlantic rainforest of South America, such as Anolis neglectus, A. pseudotigrinus, A. nasofrontalis, and A. phyllorhinus, are known from only a handful a specimens and only from a handful of localities. Together, these four species have been observed a total of eight times on iNaturalist.org (n = 2, 1, 1, and 4 observations, respectively) indicating just how uncommonly encountered they are in the field.

Beyond the Atlantic Rainforest region of Brazil, another area of concern becomes the valleys coming off the Andes mountains in countries like Peru, Ecuador, Colombia, and Venezuela. Many of the species in mountain valleys only occur in one or a few places as the mountain ridges have created barriers to dispersal both enhancing speciation as well as risk of extinction. For example, a recent paper by Moreno-Arias and colleagues (2023) split Anolis heterodermus into eight separate species all occurring in different parts of the cis-Andean valleys of Colombia. Some of the ranges of these species comprise only a few hundred square kilometers in areas not far from population centers such as Bogotá, Cali, and Medellín and most of these species are only known from a handful of observations. For example, Anolis inderenae near Bogotá has only five observations on iNaturalist while Anolis vanzolini slightly to the south has only three. Even species that are seemingly more abundant are often range limited. For example Anolis chloris has nearly 200 observations on iNaturalist but only occurs in the lowland forests along the Pacific coast of Colombia and Ecuador.

Hence, range-restricted species are probably at greatest risk throughout South America. However, small geographic distribution is not the only thing that threatens lizards of South America. Other factors such as governmental policy can either protect or threaten species.

Policy changes and their impact on local diversity has been well documented including in South America. For example, in the late 1970’s the Brazilian state of Rondonia was opened to colonization for the development of new farmland. As such, deforestation there occurred at an accelerating rate (see data and imagery). The deforestation in the western Amazon dramatically impacted natural environments on which many anole species depend (Fearnside 1982, Fearnside and de Lima Ferreira 1984). This is especially important given the enhanced extinction risk associated with forest-dwelling species (e.g., Cox et al. 2022), which describes many, if not most, anole species. So clearly, establishing protected areas can be of value as well as generally trying to reduce habitat loss.

Another major issue that is only going to grow in importance in future years is climate change. In recent years numerous papers have pointed out the risk of a changing thermal environment on lizards as regions experience both increased temperatures and variation in temperatures. Several papers stand out for discussion (e.g., Huey et al. 2009, Sinervo et al. 2010, Caetano et al. 2022, Cox et al. 2022). For example, in 2020, Diele-Viegas and colleagues pointed out that most lizard clades are vulnerable to extinction despite associated geographic distributions or local climate conditions. Their meta-analysis revealed that Neotropical regions of South and Central America were most at risk of climate-related extinctions. Given that tropical regions have the highest species diversity in general, this is not too surprising. However, vulnerability is hard to assess given that not every species was evaluated for risk. For anoles, only 98 of 427 species were evaluated as part of Diele-Viegas et al. (2010), yet their larger taxonomic clade (Iguania) was considered to be vulnerable in the Neotropical biogeographic realm unlike the Anguimorpha and Gekkota.

So at least some recent meta-analyses suggest anoles are at risk. However, some of the projections from other studies differ slightly with regards to when or where risk will occur. For example, many of the most vulnerable species or clades of lizard occur in low latitudes (Ceballos et al. 2017). However, extreme temperatures are most expected in mid-latitude regions, not the tropics (Murali et al. 2023). Murali and colleagues (2023) reported that 11.9% of environments were predicted to experience extreme thermal conditions for half the year by 2099. Another study (Cosendey et al. 2023) identified species as most at risk if they were tropical, viviparous, thermo-conformers. While not viviparous, the tropical thermo-conforming anoles (which pretty much describes all anoles in South America) are among the clades that are likely at greater risk than, say, desert reptiles. This is because desert reptiles are thought to be pre-adapted to thermal stress (Murali et al. 2023). Though not without controversy, some early projections indicate that by 2080 lizard extinction could reach 20% of all species globally (Sinervo et al. 2010), which would easily qualify as a mass extinction event.

The Path Forward

Read More

Green anoles usually perch high in the vegetation, especially in the presence of brown anoles. But here one female braved the brown bullies, presumably to prey on mosquitoes lured to the trap.

Green anoles (Anolis carolinensis) are known for their bold visual displays—vibrant dewlaps and dramatic head bobs dominate their social interactions. But at SICB 2025, Dr. Stephanie Campos highlighted an overlooked aspect of their behavior: chemical communication. Her research explores how the hormone arginine vasotocin (AVT) influences the production and interpretation of chemical signals, revealing a fascinating layer of complexity in how these lizards interact.

Dr. Campos’s work focuses on how AVT alters both the creation of chemical signals and the way they are perceived. To investigate, her team treated male anoles with AVT or a saline control and observed how untreated “receiver” males responded to these “signalers.” The researchers tracked receiver behaviors like tongue flicking—a chemosensory behavior—and analyzed their forebrain neurochemistry, specifically dopamine, norepinephrine, and epinephrine, which are linked to motivation and social behavior.

The findings revealed something remarkable: receivers interacting with AVT-treated males responded more frequently with tongue flicks and lip smacks, suggesting AVT makes chemical signals more prominent or engaging. Additionally, dopamine levels in the receivers’ forebrain typically influenced how quickly they tongue flicked in response to saline-treated males. However, when interacting with AVT-treated males, this relationship disappeared, suggesting that AVT doesn’t just enhance the chemical signals—it changes how they’re processed by receivers.

This study has big implications for understanding anoles. While their visual displays have been studied extensively, chemical communication has often been overlooked. Dr. Campos’s work suggests that AVT modulates territorial behavior by enhancing chemical signals and shaping how social information is interpreted. It highlights the need for further research into the neuroendocrine system’s role in communication, especially in animals like anoles, which rely on multiple sensory modalities to interact.

Chemical signaling in anoles, long underappreciated, is a promising area for uncovering new insights into the complexities of their social lives. This research reminds us that even subtle behaviors—like a flick of the tongue—can reveal the sophisticated ways animals navigate their social environments. As anoles continue to surprise us, it’s clear there’s much more to learn about these charismatic lizards!

For more on Dr. Campos’s work, check out her publications:

    •         Campos, S. M., et al. (2020). Arginine vasotocin impacts chemosensory behavior during social interactions of Anolis carolinensis. Hormones and Behavior, 124, 104772.

    •         Campos, S. M., et al. (2022). Signaler’s vasotocin alters the relationship between responder’s forebrain catecholamines and communication behavior in lizards (Anolis carolinensis). Brain Behavior and Evolution, 97(3-4), 184–196 .

Urbanization has introduced man-made substrates like metal rods and plastics into anole habitats. So, how does this shift in the ecosystem affect the locomotion of anole lizards that rely on the intermolecular forces between their adhesive toepads and substrates? At SICB 2025, Austin Garner, assistant professor at Syracuse University, presented his research where he explored this with Maxwell Handen and Maya Philips by looking at the climbing performance (ascending and descending) of two anole species: green anoles (Anolis carolinensis) and brown anoles (Anolis sagrei).

They investigated two main questions:

1. How do natural and urban populations of green anoles differ in their morphology?
2. How do morphological differences correspond to climbing performance of urban populations of green anoles and brown anoles?

A digital X-ray system was used to determine forelimb and hindlimb lengths. Aligning with previous research, the urban populations of both green and brown anoles were found to have longer forelimbs while brown anoles also had longer hindlimbs compared to the natural population of green anoles after accounting for body size.

The effects of these differences in morphology were evaluated by measuring and comparing the average and maximum climbing speeds of the populations using high-speed videography as they ascended and descended 45° and 90° inclines (wooden dowels covered with window screening mesh to enable robust clinging). Interestingly, natural populations of green anoles were not influenced by either the inclines or the running orientation, unlike the urban populations, which were significantly affected by the running orientation. Urban green anoles exhibited a reduction in speed as they moved downwards, which makes sense because they use their limbs as brakes. Urban brown anoles showed greater speed when climbing up, which is attributed to their longer and more muscular hindlimbs. Similarly, their descending locomotor performance was also reduced, especially when the surface was 90°. This suggests that better descending performance may require shorter strides enabled by shorter hindlimbs.

Garner is currently working on understanding and measuring the limb kinematics associated with the climbing and descending performances of these anole populations to shed light on their exact locomotor mechanisms, so stay tuned for those results!

 

The local nesting environment that anole eggs experience—temperature, substrate type, or moisture content of the soil—can be important to embryonic development.  However, there is a gap in research that combines these factors and looks at their relative contributions to the variation in offspring phenotypes.

John Rodgers, a Master’s student in Daniel Warner’s lab at Auburn University, presented his findings on this topic—which he conducted as part of his undergraduate research—at SICB 2025.

John explained how brown anoles (Anolis sagrei) are a great organism to study the effect of environmental nesting conditions on egg and embryo development, as they lay one egg at a time and there’s previous research determining that temperature and moisture of the environment can affect phenotypes of hatchlings.

For this experiment, eggs were collected from the wild and placed among eight different treatments which varied in moisture, temperature, and substrate material. From these treatments, John measured egg mass over time, time taken for full embryonic development, hatchling body size (snout-vent length), and mass. John observed that warmer temperature treatments sped up embryo development by an average of 10 days, as well as increasing egg growth over time.

John also found that increased moisture significantly increased growth of both the eggs and the hatchlings. However, the impacts of both temperature and moisture operate mainly in isolation: there doesn’t appear to be a clear interaction between these variables. Additionally, there was no significant impact of the substrate type.

Previous research from the Warner Lab has demonstrated that hatchling mass and rate of development can have fitness effects, meaning these findings could help our understanding of the potential impacts of changing environment on the survival of anoles. John continues to work with anoles, asking more questions about habitat use!

Check out John’s research in more detail here.

What Rensch (really) found there

Rensch’s rule is one of the great macroevolutionary patterns studied by evolutionary biologists. It describes the positive association between male-biased sexual size dimorphism (SSD) and species size, a relationship that has been observed in many different taxa (although it is certainly not a generalizable pattern). Since 1950, year in which Bernhard Rensch described the rule for the first time, different hypotheses for its emergence have been proposed and tested, those involving sexual selection being the most popular. For example, male-biased SSD is likely to evolve in species where larger sizes provide males of fighting advantages in encounters with other males. Moreover, female size might subsequently evolve to be larger (although to a lesser extent) due to correlated selection and/or genetic correlation. In the end, the average size of the species increases together with male-biased SSD, and we could expect this effect to be stronger in species experiencing intense sexual selection regimes.

The study of Rensch’s rule patterns has increased exponentially in the last decades, providing us with important insights about the evolution of body size and sexual dimorphism. However, I recently found out that the definition of Rensch’s rule used by most researchers is not accurate. Rensch’s rule was an important concept during my PhD so I got interested in its history and particularly in its origin. After some time spent checking old books and papers (and getting some of them translated from German) I found the truth! Rensch was not only interested in the relationship between SSD and size, but in the relationship between ANY relative sexual difference and size. The Rensch’s rule we know of today is just a special case of a more general rule! And most people seem to have ignored this for decades!

Although I was not the first to notice this inconsistency between past and present definitions (e.g., see Adams et al., 2020), I realized that a concrete presentation of this problem was needed, especially because the frequency at which Rensch’s rule studies are being published is increasing. For this reason, I decided to write a historical perspective on Rensch’s rule with a detailed explanation of this historical inaccuracy and its possible consequences (see Toyama, 2024). Part of that work is also about how testing Rensch’s rule in traits other than body size (as Rensch originally did) might illuminate other aspects of sexual dimorphism. And here is where anoles can help us, keeping the tradition of being great systems for pretty much everything.

Read More

Cuando era estudiante de pregrado en Colombia, estaba tratando de decidir qué hacer para mi tesis. En Colombia—o al menos en mi alma mater, la Universidad Icesi—es obligatorio hacer una tesis para graduarse. Durante ese tiempo, me encontré con tres de mis artículos favoritos: Janzen (1967), Ghalambor et al. (2006) y Muñoz et al. (2014). Después de leer estos artículos, una pregunta surgió en mi mente: ¿Pasa lo mismo en los Andes? Específicamente, ¿la tolerancia al frío disminuye con la elevación mientras que la tolerancia al calor permanece sin cambios?

Compartí esta idea con mis mentores de tesis, María del Rosario Castañeda y Gustavo A. Londoño, y les dije: ¡Quiero hacer esto! Quiero ver cómo los límites térmicos y la rango la tolerancia térmica varían con la elevación tanto dentro como entre las especies de Anolis.

Para abreviar, recolecté datos sobre tolerancia al frío y al calor para 14 especies de anolis en cinco sitios diferentes de Colombia. Sin embargo, debido a restricciones en la Universidad Icesi, solo pude utilizar datos de cuatro especies para mi tesis. Avancemos un año atrás, cuando estaba discutiendo este conjunto de datos con mi mentor de doctorado, Jonathan Losos. Me dijo: deberías usar estos datos para uno de tus capítulos de doctorado. Así que lo hice. Ahora, está publicado en el Evolutionary Journal of the Linnean Society: Salazar et al. 2024.

Ahora, hablemos uno de los Anolis de los Andes colombianos. La mayor parte de lo que sabemos sobre la fisiología térmica de anoles proviene de Anolis caribeños. Hay una notable falta de información sobre los límites térmicos de los anoles que habitan en los Andes. Solo un puñado de artículos se ha publicado sobre este tema: Méndez-Galeano y Calderón-Espinosa 2017, Méndez-Galeano et al. 2020, Montoya-Cruz et al. 2024 y Pinzón-Barrera et al. 2024. Sin embargo, la mayoría de estos se centran en una sola especie.

Entre 2016 y 2017, varios estudiantes de pregrado y yo visitamos cinco localidades diferentes en Colombia para medir la tolerancia al frío y al calor en los anoles andinos. Pasamos casi siete meses en el campo durante un año y medio. Medimos 367 individuos—machos, hembras y juveniles—de 14 especies a lo largo de dos clados: Draconura (cinco especies) y Dactyloa (nueve especies) a lo largo de un gradiente de elevación (200–3000 m). Nuestro estudio abordó dos preguntas clave:

1. ¿Cómo predice la variación térmica a través de la elevación la evolución de dos rasgos fisiológicos clave en los ectotermos tropicales del continente?
2. ¿Cómo ha evolucionado la fisiología térmica en la radiación andina de los anoles?

Antes de adentrarnos en los resultados, permítanme compartir algunas historias de campo. Si alguna vez han buscado Anolis en el Caribe o en los Andes, sabrán lo desafiantes que son. Antes de mis saludas de campo, Rosario me llevó en una de las suyas para enseñarme lo básico. Pasamos unos días en el campo y encontramos un par de lagartijas. En ese momento, pensé: ¡Nunca voy a encontrar suficientes lagartijas para escribir una tesis!

Encontrar anoles en los Andes es difícil. Durante el día, casi son imposibles de ver, y si logras ver uno, atraparlo es otra historia. Como rara vez tuvimos éxito durante el día, cambiamos a trabajo de campo por la noche. Incluso entonces, en algunos lugares no vimos lagartijas durante días. Para maximizar la colecta de datos, decidí capturar y medir a cada individuo que encontrase y evaluar si la lagartija era lo suficientemente grande o saludable para ser medida.

Caminando por la noche en los Andes colombianos; Parque Nacional Natural Tatamá – 2000 m. El anole que tengo en la mano es un Anolis princeps, mi especie favorita.

Aquí va una historia adicional: Rosario una vez me contó lo diferente que era atrapar Anolis en el Caribe. Dijo que allí es más fácil verlos y atraparlos, e incluso puedes decidir en el momento cuál medir. No le creí—hasta que me uní a Kristin Winchell en la República Dominicana. ¡Nunca había visto tantos anoles en un solo lugar—fue increíble! Aún así, me encanta buscar anoles en los Andes, aunque sea más desafiante. No estoy seguro de por qué, pero los Andes siempre tendrán un lugar especial en mi corazón—quizás porque uno de mis sitios de campo está a solo 30 minutos de la casa de mis padres, probablemente nunca lo sabré, jaja.

¿Qué encontramos? Como esperábamos, descubrimos que la tolerancia al frío (CTmin) y la tolerancia al calor (CTmax) aumentan con las temperaturas ambientales y operativas, pero disminuyen con la elevación. Sin embargo, contrariamente a lo que han reportado otros estudios, la tolerancia al calor no permanece sin cambios con la elevación. A diferencia de sus contrapartes caribeñas, los anoles andinos no parecen usar un mecanismo de regulación conductual para limitar la divergencia en la tolerancia al calor a través de las elevaciones—un fenómeno conocido como el efecto Bogert (Muñoz et al. 2022). Es posible que los anoles andinos no regulen su temperatura conductualmente de la misma manera que lo hacen las especies caribeñas, aunque esto aún requiere más investigación (pero véase Méndez-Galeano y Calderón-Espinosa 2017).

También encontramos que la tolerancia al frío y al calor evolucionaron a tasas similares. El análisis filogenético reveló que los límites térmicos pueden variar entre especies estrechamente relacionadas, lo que desafía la idea del conservadurismo de nicho y señala la flexibilidad en la tolerancia fisiológica a medida que las especies se diversifican a lo largo de los gradientes de elevación. Además, la compleja geografía de los Andes jugó un papel significativo en la diversidad de la fisiología térmica dentro de estos anoles. Comprender cómo la diversidad fisiológica influye en la diversificación de especies podría darnos luz sobre cómo dos clados del mismo género, con historias evolutivas distintas, muestran respuestas similares a la adaptación a ambientes montañosos. Nuestros datos sobre los anoles andinos son consistentes con esta perspectiva: ya sea cerca del nivel del mar o varios kilómetros por encima de él, las especies están fisiológicamente especializadas para sus condiciones térmicas locales y exhiben un rango de tolerancia relativamente estrecho, como se predice para los lagartos tropicales (Huey et al. 2009).

Para responder a esas dos preguntas:

1. ¿Cómo predice la variación térmica a través de la elevación la evolución de dos rasgos fisiológicos clave en ectotermos tropicales de tierras continentales? La tolerancia al frío y al calor disminuye con la elevación.
2. ¿Cómo ha evolucionado la fisiología térmica en la radiación andina de los anoles? Ambos rasgos evolucionan a tasas similares, pero su evolución es independiente de la filogenia.

En un mundo que se calienta rápidamente, la pregunta crítica es si estas especies podrán mantener el ritmo con los impactos acelerados del cambio climático en sus ambientes naturales. La investigación futura debe centrarse en comprender cómo el aumento de las temperaturas y los patrones cambiantes de lluvia influirán en los patrones de actividad, el equilibrio energético y las tasas de crecimiento poblacional de los anoles andinos. Al vincular la variación fisiológica con las tendencias demográficas, podremos predecir mejor cómo estas notables especies de lagartos podrían enfrentar las presiones del cambio global.

Espero que este estudio despierte la curiosidad por explorar más a fondo los anoles andinos—y también los anoles amazónicos, que siguen siendo sorprendentemente poco estudiados.

Una última historia adicional—no estoy seguro de cuántos de ustedes han visto esta foto, pero tomé esa hermosa imagen de Anolis chloris durante uno de mis viajes de campo cuando era estudiante de pregrado.

 

References:

Salazar JC, Londoño GA, Muñoz MM, et al. The Andes are a driver of physiological diversity in Anolis lizards, Evolutionary Journal of the Linnean Society 2025; 4(1): kzae040. https://doi.org/10.1093/evolinnean/kzae040

Ghalambor CK, Huey RB, Martin PR, et al. Are mountain passes higher in the tropics? Janzen’s hypothesis revisited, Integrative and Comparative Biology 2006; 46: 5-17. https://doi.org/10.1093/icb/icj003

Janzen DH. Why mountain passes are higher in the tropics, The American Naturalist 1967; 101: 233-249. https://www.jstor.org/stable/2458977

Méndez-Galeano MA, Calderón-Espinosa ML. Thermoregulation in the Andean lizard Anolis heterodermus (Squamata: Dactyloidae) at high elevation in the Eastern Cordillera of Colombia, Iheringia, Série Zoologia 2017; 107: e2017018. https://doi.org/10.1590/1678-4766e2017018  

Méndez-Galeano MA, Paternima-Cruz RF, Calderón-Espinosa ML. The highest kingdom of Anolis: Thermal biology of the Andean lizard Anolis heterodermus (Squamata: Dactyloidae) over an elevational gradient in the Eastern Cordillera of Colombia, Journal of Thermal Biology 2020; 89: 102498. https://doi.org/10.1016/j.jtherbio.2019.102498

Montoya-Cruz A, Díaz-Flórez RA, Carvajalino-Fernández JM. Thermal balance in Andean lizards: A perspective from the high mountains, Austral Ecology 2024; 49: 313578. https://doi.org/10.1111/aec.13578

Muñoz MM, Stimola MA, Algar AC, et al. Evolutionary stasis and lability in thermal physiology in a group of tropical lizards, Proceedings of the Royal Society B 2014; 281: 20132433. https://doi.org/10.1098/rspb.2013.2433

Muñoz MM. The Bogert effect, a factor in evolution, Evolution 2022; 76: 49-66. https://doi.org/10.1111/evo.14388

Pinzón-Barrera C, Suárez-Ayala N, Carrillo-Chávez LM, et al. Unveiling critical thermal limits of Anolis tolimensis (Squamata, Anolidae) across an elevational landscape, Current Herpetology 2024; 43: 155-134. https://doi.org/10.5358/hsj.43.115

When I was an undergrad student back in Colombia, I was trying to decide what to do for my thesis. In Colombia—or at least at my alma mater, Universidad Icesi—it’s mandatory to complete a thesis to graduate. During this time, I stumbled upon and read three of my favorite papers: Janzen (1967), Ghalambor et al. 2006, and Muñoz et al. (2014). After reading those papers, a question popped into my mind: Does the same happen in the Andes? Specifically, does cold tolerance decrease with elevation while heat tolerance remains unchanged?

I shared this idea with my thesis mentors, María del Rosario Castañeda and Gustavo A. Londoño, and told them, I want to do this! I want to test how thermal limits and thermal tolerance breadth vary with elevation both within and among anole species.

Long story short, I collected data on cold and heat tolerance for 14 anole species across five different sites in Colombia. However, due to restrictions at Universidad Icesi, I could only use data from four species for my thesis. Fast forward to over a year ago, when I was discussing this dataset with my PhD mentor, Jonathan Losos. He said, you should use this data for one of your PhD chapters. So, I did. Now, it’s published in the Evolutionary Journal of the Linnean Society: Salazar et al. 2024.

Now, let’s talk about Colombian Andean anoles. Most of what we know about the thermal physiology of anoles comes from Caribbean species. There’s a noticeable gap in information about the thermal limits of Andean-dwelling anoles. Only a handful of papers have been published on this topic: Méndez-Galeano and Calderón-Espinosa 2017, Méndez-Galeano et al. 2020, Montoya-Cruz et al. 2024, and Pinzón-Barrera et al. 2024. However, most of these focus on a single species.

Between 2016 and 2017, several undergrad students and I visited five different locations in Colombia to measure cold and heat tolerance in Andean anoles. We spent nearly seven months in the field over a year and a half. We measured 367 individuals—males, females, and juveniles—from 14 species across two clades: Draconura (five species) and Dactyloa (nine species) along an elevation gradient (200–3000 m). Our study addressed two key questions:

1. How does thermal variation across elevation predict the evolution of two key physiological traits in tropical mainland ectotherms?
2. How has thermal physiology evolved in the Andean radiation of anole lizards?

Before diving into the results, let me share some fieldwork stories. If you’ve ever searched for anoles in the Caribbean or the Andes, you’ll know the challenges. Before my trips, Rosario took me along on one of hers to teach me the basics. We spent a few days in the field and found a couple of lizards. At the time, I thought, I’ll never find enough lizards to write a thesis!

Finding anoles in the Andes is tough. During the day, they’re almost impossible to spot, and if you do see one, catching it is another story. Since I rarely succeeded during the day, we shifted to fieldwork at night. Even then, in some locations we didn’t see lizards for days. To maximize data collection, I decided to capture and measure every individual I found and assess whether the lizard was big or healthy enough to be measured.

Walking through the night in the Colombian Andes; Parque Nacional Natural Tatamá – 2000m,. The anole I have in my hand is an Anolis princeps, my favorite species.

Here’s a side story: Rosario once told me how different it was to catch anoles in the Caribbean. She said it’s easier to see and catch them there, and you can even decide on the spot which one to measure. I didn’t believe her—until I joined Kristin Winchell in the Dominican Republic. I had never seen so many anoles in one place—it was unbelievable! Still, I love searching for anoles in the Andes, even though it’s more challenging. I’m not sure why, but the Andes will always hold a special place in my heart—maybe it’s because one of my field sites is just 30 minutes from my parents’ house, probably I’ll never know haha.

What did we find? As expected, we found that cold tolerance (CTmin) and heat tolerance (CTmax) increase with environmental and operative temperatures but decrease with elevation. However, contrary to what other studies have reported, heat tolerance does not remain unchanged with elevation. Unlike their Caribbean counterparts, Andean anoles do not appear to use behavioral buffering to limit divergence in heat tolerance across elevations—a phenomenon known as the Bogert effect (Muñoz et al. 2022). It’s possible that Andean anoles do not thermoregulate behaviorally in the same way Caribbean species do, though this still requires further investigation (but see Méndez-Galeano and Calderón-Espinosa 2017).

We also found that cold and heat tolerance evolved at similar rates. Phylogenetic analysis revealed that thermal limits can vary among closely related species, challenging the idea of niche conservatism and pointing to flexibility in physiological tolerance as species diversified along elevation gradients. In addition, the Andes’ complex geography played a significant role in driving the diversity of thermal physiology within these anoles. Understanding how physiological diversity influences species diversification could shed light on how two clades from the same genus, with distinct evolutionary histories, exhibit similar responses to adapting to mountainous environments. Our data on Andean anoles are consistent with this perspective: whether near sea level or several kilometers above it, species are physiologically specialized to their local thermal conditions, and exhibit relatively narrow tolerance breadth, as predicted for tropical lizards (Huey et al. 2009).

To answer those two questions:

1. How does thermal variation across elevation predict the evolution of two key physiological traits in tropical mainland ectotherms? Cold and heat tolerance decreases with elevation.
2. How has thermal physiology evolved in the Andean radiation of anole lizards? Both traits evolve at similar rate, but their evolution is independent of the phylogeny.

In a rapidly warming world, the critical question is whether these species can keep pace with the accelerating impacts of climate change on their natural environments. Future research should focus on understanding how rising temperatures and shifting rainfall patterns will influence the activity patterns, energy balance, and population growth rates of Andean anoles. By linking physiological variation to demographic trends, we can better predict how these remarkable lizards might fare under the pressures of global change.

I hope this study sparks curiosity to further explore Andean anoles—and even Amazonian anoles, which remain surprisingly understudied.

One last side story—I’m not sure how many of you have seen this picture, but I took that beautiful shot of Anolis chloris during one of my field trips as an undergrad.

 

References:

Salazar JC, Londoño GA, Muñoz MM, et al. The Andes are a driver of physiological diversity in Anolis lizards, Evolutionary Journal of the Linnean Society 2025; 4(1): kzae040. https://doi.org/10.1093/evolinnean/kzae040

Ghalambor CK, Huey RB, Martin PR, et al. Are mountain passes higher in the tropics? Janzen’s hypothesis revisited, Integrative and Comparative Biology 2006; 46: 5-17. https://doi.org/10.1093/icb/icj003

Janzen DH. Why mountain passes are higher in the tropics, The American Naturalist 1967; 101: 233-249. https://www.jstor.org/stable/2458977

Méndez-Galeano MA, Calderón-Espinosa ML. Thermoregulation in the Andean lizard Anolis heterodermus (Squamata: Dactyloidae) at high elevation in the Eastern Cordillera of Colombia, Iheringia, Série Zoologia 2017; 107: e2017018. https://doi.org/10.1590/1678-4766e2017018  

Méndez-Galeano MA, Paternima-Cruz RF, Calderón-Espinosa ML. The highest kingdom of Anolis: Thermal biology of the Andean lizard Anolis heterodermus (Squamata: Dactyloidae) over an elevational gradient in the Eastern Cordillera of Colombia, Journal of Thermal Biology 2020; 89: 102498. https://doi.org/10.1016/j.jtherbio.2019.102498

Montoya-Cruz A, Díaz-Flórez RA, Carvajalino-Fernández JM. Thermal balance in Andean lizards: A perspective from the high mountains, Austral Ecology 2024; 49: 313578. https://doi.org/10.1111/aec.13578

Muñoz MM, Stimola MA, Algar AC, et al. Evolutionary stasis and lability in thermal physiology in a group of tropical lizards, Proceedings of the Royal Society B 2014; 281: 20132433. https://doi.org/10.1098/rspb.2013.2433

Muñoz MM. The Bogert effect, a factor in evolution, Evolution 2022; 76: 49-66. https://doi.org/10.1111/evo.14388

Pinzón-Barrera C, Suárez-Ayala N, Carrillo-Chávez LM, et al. Unveiling critical thermal limits of Anolis tolimensis (Squamata, Anolidae) across an elevational landscape, Current Herpetology 2024; 43: 155-134. https://doi.org/10.5358/hsj.43.115