Year: 2013 Page 20 of 37

Anolis cristatellus basking in the sun. Photo by Janson Jones.

In recent years, concern has arisen about how tropical ectotherms will cope with rising temperatures. For a variety of reasons, tropical species are considered particularly vulnerable, and coarse scale modelling exercises suggest that many populations and species may face extinction in the near future. Some of the most influential studies, such as Sinervo et al.’s mammoth 2010 paper (already cited more than 200 times!), have focused on lizards.

The field of thermal ecological physiology made great advances in the 1970’s and 80’s and a, perhaps the, major player in the work was research on lizards. And amongst this work, studies on Anolis played a particularly prominent role (reviewed in Chapter 10 of Lizards in an Evolutionary Tree). Hence, it is no surprise that a reconsideration of lacertilian prospects, based on detailed understanding of how lizards interact physiologically with their environment, is stemming from in-depth studies on anoles.

Most modelling studies are based on a coarse-grained (1 km² resolution), remote sensing scale analysis of global temperature variation, with the assumption that relatively little variation in thermal environment occurs within each block. Recent papers focusing on anoles in Puerto Rico (Leal and Gunderson, 2012) and offshore islands in Honduras (Logan et al., 2013) have tested this idea and found it wanting–in open areas and, to a lesser extent, within forests–considerable thermal heterogeneity occurs. Moreover, many anole species thermoregulate behaviorally–i.e., they aren’t passive samplers of the environment, their body temperature a simple reflection of the ambient, but rather they move in and out of sun and shade, and thus can determine their temperature, mediating what is available in the environment. Thus, even if the environment gets warmer, lizards may have the option simply to switch to increased use of the cooler micro-environments, maintaining the same body temperature.

Plateau in peak sprinting performance in relation to body temperature in Anolis cristatellus. Increases in body temperature over the range of ca. 31-36 C will have little effect. Figure from Gunderson and Leal (2012).

A third point is relevant as well. Physiological performance is generally temperature-dependent, but often a broad plateau exists in which maximal performance varies over a broad range of body temperatures. Hence, populations may be buffered from effects of increased temperatures if the resulting increase in body temperature does not push them off the plateau.

Both studies ask the simple question: if global temperatures go up, will lizards in open and forested habitats experience an increase or a decrease in the quality of the thermal environment, quantified in terms of how readily they are able to achieve their optimal temperature (using sprint speed as a proxy).

Anolis bicaorum from Utila, one of the forest species in the Logan et al. study. Photo by J. Losos.

The results show interesting similarities and differences.

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Anolis allisoni, the green lizard wearing a blue jumper. Photo by J. Losos.

Female A. gorgonae. Photo by Joe Burgess.

Two of the world’s coolest lizards are blue anoles, male A. allisoni from Cuba and both sexes of the fabled blue anole of Gorgona (A. gorgonae). Why the blue? Heck if I know. You can see a male allisoni on a palm from a great distance, so it amazes me that they can survive. Seems clear that they must be trying to advertise their presence. On the other hand, I’m told that A. gorgonae can be very hard to spot when one looks up toward the canopy, where the species hangs out. In this instance, the blue may actual serve for crypsis. Who knows?

Lets not forget the blue toes of Anolis bartschi! Photo by Joe Burgess.

Turns out that there are lots of blue animals and the reason for their blueness, as well as the mechanism by which it is produced, is not well known. Kate Umbers has just published a nice review in Journal of Zoology on all things blue, and it’s a worthwhile read, even if she didn’t mention anoles, or even hardly any lizards at all. Among other interesting tidbits, she points out that dichotomizing colors as structural or pigmentary is somewhat misleading, because both pigments and structure can work together to produce blue colors. Also, blue-footed boobies’ feet are bluer when they’re well-fed, and female boobies invest more in their offspring if they have brighter blue feet.  Who knows what interesting blue-related aspects of natural history remain to be uncovered in anoles?

Many anoles have blue eyes as well, and this is a trait that seems to pop up repeatedly throughout the clade, though I have no data on this. I wonder what’s up with that.

Anolis peraccae. Photo by Alejandro Arteaga.

As a final bonus, here’s a video of a blue knight anole! (and here’s a previous AA post on the same). The video itself isn’t so sharp, but it’s a blue knight anole!

httpv://www.youtube.com/watch?v=hwHhyqTmqrk&feature=youtu.be&a

Some like it hot. Anolis allisoni on Roatan, an inhabitant of open areas, will benefit from increased global temperatures. Photo by J. Losos.

Thanks to HerpDigest, a regular email compendium of herpetological news, here is a press release on a recent paper in Global Change Biology:

A new Dartmouth College study finds human-caused climate change may have little impact on many species of tropical lizards, contradicting a host of recent studies that predict their widespread extinction in a rapidly warming planet.

Most predictions that tropical cold-blooded animals, especially forest lizards, will be hard hit by climate change are based on global-scale measurements of environmental temperatures, which miss much of the fine-scale variation in temperature that individual animals experience on the ground, said the article’s lead author, Michael Logan, a Ph.D. student in ecology and evolutionary biology.

To address this disconnect, the Dartmouth researchers measured environmental temperatures at extremely high resolution and used those measurements to project the effects of climate change on the running abilities of four populations of lizard from the Bay Islands of Honduras. Field tests on the captured lizards, which were released unharmed, were conducted between 2008 and 2012.

Anolis bicaorum, a denizen of closed forest, from Utila, Honduras. Photo by J. Losos.

Previous studies have suggested that open-habitat tropical lizard species are likely to invade forest habitat and drive forest species to extinction, but the Dartmouth research suggests that the open-habitat populations will not invade forest habitat and may actually benefit from predicted warming for many decades. Conversely, one of the forest species studied should experience reduced activity time as a result of warming, while two others are unlikely to experience a significant decline in performance.

The overall results suggest that global-scale predictions generated using low-resolution temperature data may overestimate the vulnerability of many tropical lizards to climate change.

Another photo of A. allisoni, just because they’re so cool. Photo by J. Losos

“Whereas studies conducted to date have made uniformly bleak predictions for the survival of tropical forest lizards around the globe, our data show that four similar species, occurring in the same geographic region, differ markedly in their vulnerabilities to climate warming,” the authors wrote. “Moreover, none appear to be on the brink of extinction. Considering that these populations occur over extremely small geographic ranges, it is possible that many tropical forest lizards, which range over much wider areas, may have even greater opportunity to escape warming.”

An example of open habitat, from the island of Cayo Menor. Photo by Mike Logan.

An example of closed forest, from the island of Roatan. Photo by Mike Logan.

Story Source: The above story is reprinted from materials provided by Dartmouth College, via EurekAlert!, a service of AAAS.