One of the tell-tale signs that you’re in the tropics in the Western Hemisphere is the abundance of anoles scampering about on palm trees. Tropical anoles tend to get all the media attention. The lowland tropical taxa are the anole media darlings, such as the jewel-toned Lesser Antillean anoles, the flashy trunk-crown anoles, such as A. allisoni, and the determined invaders, like A. sagrei. Personally, I’m a bigger fan of the montane anoles. These species tend to get less attention. They’re usually fairly drab in coloration and, by definition, they live in more inhospitable environments that are remote and difficult to access. These are the anoles that live where the 4×4 can’t penetrate, where the cold rain pounds even in the dead of summer, and where the lush tropical communities of the lowlands morph into endless stands of lonely pine trees.
And, even if they usually lack the pigmented pizazz of the lowland anoles, the montane species have a mystery that is all their own. How is it that lizards bearing a tropical ancestry can tolerate the harsh environments found at high elevation? Do they use behavior to mitigate the cold? Do they evolve their physiology? To date we still have more questions than answers, but as a community we’re slowly beginning to build our knowledge of what makes highland anoles tick.
A study by Gunther Köhler and colleagues in a recent issue of Herpetology Notes focuses on a truly enigmatic species, Anolis omiltemanus. To say this montane species from the Guerrero region of Mexico is poorly understood is an understatement. What little we know of A. omiltemanus comes from a handful of studies conducted a few decades ago. Beyond the fact that these lizards have been found in leaf litter and in small shrubs in the pine and oak forests near Omiltemi, very little is known about their ecology.
In November 2012 Köhler and colleagues ventured to the Guerrero region in search of this elusive species so as to collect specimens for morphological analysis and gather some information on its natural history. About 7 kilometers east of Omiltemi, at a pine forest the locals call “La Laguna” about 1,920 meters above sea level, the researchers were able to find A. omiltemanus. Like so many high elevation sites in the tropics, La Laguna appears much more reminiscent of the Northeastern United States to me than of Mexico. The authors describe the site as composed of mostly pine trees with a few oak trees, which were fairly well-spaced, allowing ample light to flood between them.
Here A. omiltemanus is locally abundant, as the authors were able to capture 10 individuals while night herping. The sleeping anoles were all caught on vegetation between 2 and 5 meters above the ground. In an effort to see what these lizards do during the day, they returned to the site during the afternoon only to find that their quarry was nowhere to be found. While the possibility that there simply were no more anoles to be observed at La Laguna exists, the authors reckoned it was more likely that A. omiltemanus perches fairly high up in the canopy or that the lizards were extraordinarily effective at shifting to the other side of branches to avoid being spotted. Indeed, among the little information that is known about this species is that it is predominantly arboreal. The authors observed that, when placed on the ground, these lizards move about in a somewhat clumsy manner and add that its limbs are particularly short and reminiscent of the arboreal species, A. pentaprion.
The fact that this species apparently has a predilection for pine trees is actually quite surprising to me. For my PhD I focus on the cybotoid anoles, a clade whose members range everywhere from sea level to over 3,000 meters in elevation on the Caribbean island of Hispaniola. I, too, have observed anoles that make their living near 2,000 meters, but the cybotoids are far from arboreal at those elevations. In upland environments the cybotoids spend most of their time on rocks, and split their sleeping sites between rocks and vegetation. The cybotoids appear to be fairly effective at thermoregulating, at least during the day, and have body temperatures that are comparable to their lowland counterparts. Rocks are certainly warmer and more thermally sheltered than pine trees, so my gander is that these Mexican montane lizards are routinely exposed to cold temperatures, even during the day. During the course of their study, the authors recorded nighttime temperatures as low as 4.5°C.
Needless to say, it would be fascinating to study this species’ thermal physiology, such as their preferred temperature, tolerance to heat, and tolerance to cold. Given that they appear to spend their time, even during the day, on vegetation, I imagine that they would have a fairly lower preferred temperature, impaired tolerance to heat, and a strong tolerance to cold as compared to related species in the lowlands. If this is true, then the mechanisms by which anoles adapt to cold environments can likely differ among clades. I hope that this study foments more work on A. omiltemanus and other montane anoles, so that we can begin to discover the varied ways in which these tropical lizards contend with cold environments.
Gunther Köhler, Raúl Gómez Trejo Pérez, Marcos García Pareja, Claus Bo P. Petersen, and Fausto R. Méndez de la Cruz. 2013. Notes on Anolis omiltemanus Davis, 1954 (Reptilia: Squamata: Dactyloidae). Herpetology Notes 6: 401-412.