Illustration of Anolis heterodermus on a Frailejon inflorescence (Espeletia grandiflora). Illustration: Sebastian Perez.

Continuing with my adventure with Phenacosaurus (see Part 1 here), during the process of publishing papers from my thesis about thermoregulation in the high Andean lizard Anolis heterodermus , I realized that I only studied  one population of this species, but some populations living above 3000 meters of elevation in the subparamo and paramo tropical andes ecosystems, as well as others that are below 2600 m. Furthermore, Martha and I evaluated only thermoregulation, but other thermal traits remains unknown. Despite not having grants and without have been a postgraduate thesis, I decided to expand my research and study whether  thermoregulation, thermal tolerances and thermal sensitivity vary with elevation. I expected to find that at high elevation, lizards would be more active thermoregulators, eurythermal and cold tolerant, as happens in other Anolis lizards like the cristatellus and cybotes species groups.

To investigate these questions, I took new data during 2016 with Martha Calderón at two new localities: Chicaque Natural Park, a cloud forest reserve at 2000-2600 m elevation, and Matarredonda Ecological Park, a subparamo to paramo reserve at 3200-3400 m elevation. This time we invited our colleague and Martha Msc. student Felipe Paternina, who had done his thesis research on thermoregulation and extinction risk by climate change in the high-Andean nocturnal snake Atractus crassicaudatus. We also took data on Gachancipa, a municipality close to Tabio. At the beginning of this year, after the Covid-19 Pandemic, fortunately our second paper was published in the Journal of Thermal Biology.

 

Chicaque Natural Park (left) and Matarredonda Ecological Park (right) 

First of all, we did not find changes in thermal preference range between the three localities. Similarly, cold tolerance (CTmin) and thermal performance breadth were similar along the elevational gradient. Nevertheless, the most exciting discovery was that cold tolerance (CTmin) is very low (4.4°C in Matarredonda) and thermal performance ranges are wide. Surprisingly, CTmin in Chicaque, the lowest altitude, was 6.2°C, even though the potential lowest body temperatures at night could be only 10°C (calculated as operative temperatures with our null-models of Anolis heterodermus). This clue makes us think that maybe cold tolerance is constant due to a niche conservatism: during Pleistocene glaciations, Andean ecosystems were colder than now, and maybe this trait did not evolve when climate became warmer because there is no selective pressure for that. Definitely, Anolis heterodermus is the king mountain of anoles (in fact, it has a co-osified cranial crown).

 

Vertical thermal gradient to measure thermal preference of Anolis heterodermus. Figure from Méndez-Galeano & Calderón-Espinosa (2017)

Null model of Anolis heterodermus to measure operative temperatures in the field; in this case, the model was placed on a potential perch.

As well as with cold tolerance and thermal preference, critical thermal maximum and thermal sensitivity did not change with elevation; however, thermoregulation does: at both low and high elevations, this species has to face thermal constrains, like a cold and narrow temperature range of the Chicaque cloud forest due to its canopy cover, or the extreme fluctuating temperatures, with tendency to the coolest regimes in our study, in the Matarredonda subparamo. To deal with that, individuals become thermoconformers, contrasting in this mode with the seasonal trends in thermoregulation in Tabio. We attribute this change to the fact that seasonal changes can be behaviorally compensated with active thermoregulation, but elevational changes are more extreme, and the species have to resign to be active at suboptimal temperatures and exist under the cold range of this extreme ecosystem.

Measuring locomotor performance to assess thermal sensitivity on Anolis heterodermus. There is a very slow lizard, which the local people call “The Andean Chameleon.”

Thermoregulatory adjustments also exist at other temporal scales, such as day-by-day. At the highest elevation, subparamo and paramo days could be extremely different from one day to the next; on some days, the sun could burn your face, while on other days, you could not see anything due to the cloud cover. So, we evaluated thermorregulation between these regimes, too, and observed that on cloudy days, Anolis heterodermus remained a thermoconformer, but on sunny days, the thermal quality of the habitat offered some optimal microhabitats, and this species takes advantage by changing from thermoconformity to active thermoregulation on a daily temporal scale. Undoubtedly, this species is a thermo-oportunist, plastic in its thermoregulation, and showing us that general patterns observed at only one scale do not always tell the complete story.

Our findings placed this species closer to the static hypothesis of the evolution of thermal physiology due to behavioral buffering on selection, better known as “The Bogert Effect.” Also, thermoregulation is so dynamic, that Anolis heterodermus can be an active thermoregulator in high thermal quality habitats (or times) and a thermoconformer when the habitat become so cold or so fluctuating that thermoregulation is not feasible.

Other reptiles from the Bogotá Savannah, Eastern Cordillera of Colombia, which could be at extinction risk by climate change and which we study in our research group. From left to right: Anadia bogotensis, Atractus crassicaudatus*, Riama striata, Stenocercus trachycephalus. Photos: *Uber Rozo, Guido Fabian Medina.

Now, after all of this, the cold reign of our highland king is threatened by climate change, the effect of which could be devastating for tropical biota, especially to endemic species. Climate change puts high-elevation reptiles in a vulnerable situation due to a restricted possibility to distributional displacements, taking them to a dead end, upwards, what is called “the mountaintop extinctions.” Now it is our responsibility to, at least, predict the potential extinction risk by climate change of Anolis heterodermus and other co-distributed reptiles with our thermal data in order to prevent the possible loss of our cool-cold anole forever. Stay tuned for the final part of this trilogy of the thermal biology of Anolis heterodermus, our Andean chameleon.

 

Cites:

Méndez-Galeano, M. A., & Calderón-Espinosa, M. L. (2017). Thermoregulation in the Andean lizard Anolis heterodermus (Squamata: Dactyloidae) at high elevation in the Eastern Cordillera of Colombia. Iheringia. Série Zoologia 107.

Méndez-Galeano, M. A., Paternina-Cruz, R. F., & Calderón-Espinosa, M. L. (2020). 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 89: 102498.

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