The Andes Are a Driver of Physiological Diversity in Anolis Lizards

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:

How does thermal variation across elevation predict the evolution of two key physiological traits in tropical mainland ectotherms?
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:

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.
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