From the Herping in Cuba Facebook page (with permission).
Author: Jonathan Losos Page 17 of 130
Professor of Biology and Director of the Living Earth Collaborative at Washington University in Saint Louis. I've spent my entire professional career studying anoles and have discovered that the more I learn about anoles, the more I realize I don't know.
Anolis carolinensis from North Carolina. Photo by Graham Reynolds.
In response to a previous post on North Carolina anoles, AA reader John Philips asks:
Anyone notice a significant reduction in the population of anoles in SE NC? I live on Bradley Creek in Wilmington, NC and I have noticed very few this year. Used to see 3-5 per day sitting on various surfaces in the sun while walking my dogs, especially because my shihpoo is always “hunting” them. However, this year I probably only see 1 per week.
I assume this could be due to the cold winter? Any other predators that might have reduced the population? We have seen an increase in brown thrashers in the area and thought since they forage on the ground they might be a predator?
Guadeloupean anole (Anolis marmoratus) feeding on the back of a Lesser Antillean iguana. Photo courtesy Jérôme Guerlotté.
Jérôme Guerlotté of the Muséum National d’Histoire Naturelle in Paris reports:
“As in a new Jean De la Fontaine fable “L’iguane et l’Anolis“, this intrepid anole (Anolis marmoratus marmoratus) on Guadeloupe had just hunted a fly on the back of this Lesser Antillean iguana (Iguana delicatissima) (top) and rids it of small insects on the snout (bottom).”
Who knows what yummy morsels reside on the snout of an iguana? Photo courtesy Jérôme Guerlotté.
Anolis krugi. Photo by Manuel Leal from the Leal Lab webpage
Anole biologists are fascinated by the variation in dewlap colors and patterns both within and between species. One popular hypothesis is that dewlaps are adapted to be easily detectable against the background in which they are found. A variety of tests have been published, correlating dewlap colors with ambient light, background vegetation and other characteristics. Now Alex Gunderson and colleagues have developed an experimental method of directly testing the hypothesis. Manuel Leal, a coauthor on the paper, reports on the pages of Chipojo Lab, reprinted here:
Brighter is not always better
Those that follow the Chipojoblog are familiar with one of our core tenets: strive as best you can to design experiments under natural conditions. This philosophy reflects my own view that behavior should be studied in the field whenever possible. Our recent paper in Current Zoology, “Visual playback of colorful signals in the field supports sensory drive for signal detectability,” is a prime of example of the power of this approach, in which an intimate understanding of the ecology and behavior of anoles was used to test a major prediction of the sensory drive hypothesis: are signals locally adapted? In other words, are dewlaps locally adapted to effectively grab the attention of an inattentive receiver?
Over the years we have published a series of papers supporting the hypothesis that dewlap diversity can be partially explained by selection to increase the probability of detection. However, until this paper, experimental evidence from the field was missing, in part because manipulating dewlaps of live anoles is not trivial. Furthermore, even if we were able to successfully manipulate dewlaps, there are still many other signals (e.g., body color, motion pattern, size and posture) that would be out of our control. This problem was solved by researchers working with acoustic signals a long time ago by figuring out ways to play the signal of interest in isolation in what have become known as ‘playback experiments.’ We stole a page from their book and constructed a remote-control dewlap apparatus, which provided an opportunity to display only the dewlap under natural conditions (see gizmo below). Alex’s building and painting skills was key to the success of this gizmo. He was able to construct dewlaps with similar reflective and transmission properties of real dewlaps while taking into account the visual system of the anoles (please see papers for details).
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| Control-remote dewlap display apparatus. A) Acrylic box within which electrical components were housed. B) Electrical components. C) The apparatus at a mesic site with a fake dewlap displayed. |
Besides presenting the dewlaps in the field, we wanted to test the hypothesis that the dewlaps are locally adapted. Under this hypothesis, increased detection in one habitat comes at the cost of decreased detection in another habitat. This functional approach to test for adaptive value of a trait is commonly used as robust evidence to support selection favoring the evolution of the trait in question. In this paper we tested if the observed differences in dewlap brightness between xeric and mesic populations of Anolis cristatellus is adaptive. If so, dewlaps from mesic populations should be more detectable in mesic habitats and dewlaps from xeric habitats should be more detectable in xeric habitats. Furthermore, detection probability should decrease in the ‘wrong’ habitat. Below are the results of the experiments. In A. cristatellus individuals from xeric habitats have dewlaps which are darker, that is less brighter, than individuals from mesic populations.
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| Responses of free-ranging A. cristatellus to fake dewlaps that mimic the brightness properties of real dewlaps. |
Our findings support the sensory drive hypothesis and strongly suggest that the brightness properties of A. cristatellus dewlaps are locally adapted via selection on signal detectability. Furthermore, we have demonstrated that a brighter signal is not always the most detectable or effective signal. A common misconception, which is partially the result of not including the sensory system and habitat conditions as part of the analysis. Studies addressing potential functions and selective forces promoting the diversity of dewlaps found in anoles have flourished over the last decade, nevertheless, these results are the best experimental evidence that we have to support the hypothesis that diversity of dewlap colors might be partially explained by local adaptions to habitat light conditions and the best smoking gun to support the idea that diversity of dewlap colors can be the result of local adaptations to habitat light conditions. Additionally, our study once again underlines the need to measure both reflection and transmission when asking questions regarding the potential function of the dewlap because the two combine to determine dewlap coloration (brightness, coloration, etc.) in the real world.
From Card et al. 2018
Shane Campbell-Staton and colleagues have just published a paper in Molecular Ecology on the physiological and regulatory basis of variation in cold tolerance across the range of Anolis carolinensis. In the same issue, Daren Card and colleagues have written a very nice, freely available, summary of that article. Here’s the abstract from Card et al.’s review:
How does climate variation limit the range of species and what does it take for species to colonize new regions? In this issue of Molecular Ecology, Campbell-Staton et al. (2018) address these broad questions by investigating cold tolerance adaptation in the green anole lizard (Anolis carolinensis) across a latitudinal transect. By integrating physiological data, gene expression data and acclimation experiments, the authors disentangle the mechanisms underlying cold adaptation. They first establish that cold tolerance adaptation in Anolis lizards follows the predictions of the oxygen- and capacity-limited thermal tolerance hypothesis, which states that organisms are limited by temperature thresholds at which oxygen supply cannot meet demand. They then explore the drivers of cold tolerance at a finer scale, finding evidence that northern populations are adapted to cooler thermal regimes and that both phenotypic plasticity and heritable genetic variation contribute to cold tolerance. The integration of physiological and gene expression data further highlights the varied mechanisms that drive cold tolerance adaptation in Anolis lizards, including both supply-side and demand-side adaptations that improve oxygen economy. Altogether, their work provides new insight into the physiological and genetic mechanisms underlying adaptation to new climatic niches and demonstrates that cold tolerance in northern lizard populations is achieved through the synergy of physiological plasticity and local genetic adaptation for thermal performance.
Photo by Dee Simpson
AA reader Dee Simpson reports:
I recently found a deceased Green (Carolina) Anole near my home in central Florida. What struck me is that it was blue. At first, I thought just looked blue because it was desiccated, but on further examining the picture, I realized that one leg was green – if it was just the decaying process, I would expect the whole thing to be the same color/state. I came across the entry on your Anole Annals page regarding blue Carolina Anoles in Florida and was wonder if this could be one of those? Or is it just at a stage of decomposition where the color is weird?
Anolis gundlachi prefers to perch in the shade near the ground — according to a new study, these microclimate differences drove some of the later diversification of anoles.
Credit: Manueal Leal, MU Division of Biological Sciences
Report of a new study from the webpages of ScienceDaily, produced initially by the University of Missouri:
The islands of Puerto Rico, Cuba, Hispaniola, and Jamaica — collectively known as the Greater Antilles — are home to more than 100 species of Anolis lizards. The success of this colorful group of reptiles is often attributed to the evolution of distinct body shapes and behaviors that allow species to occupy different ecological niches. A new study from an international team of biologists including from the University of Missouri reports that the evolution of physiological differences that allow these lizards to take advantage of different microclimates (e.g., sun vs. shade) may have been just as important as these physical differences. The study, which was published recently in The Proceedings of the Royal Society B, has implications for predicting how well these lizards will cope with climate change.
“Why are there so many species of anoles? That’s the big question,” says Manuel Leal, an associate professor of biological sciences at MU and one of the authors of the report. “The notion that morphological differences alone drove the amazing diversity of anoles is missing an important part of the puzzle.”
For scientists, the Greater Antillean anoles represent a classic example of an evolutionary process known as adaptive radiation. After appearing on each of the four islands about 50 million years ago, the colorful lizards quickly diversified to exploit different niches on the island’s trees, including the canopy, trunk near the ground, mid-trunk, and other twigs. Each new species developed its own distinct body type, called an ecomorph, adapted to the niche where it lived. According to Leal, this focus on differences in appearance leaves some important questions unanswered.
“How can similar species coexist without outcompeting one another? One of the tenants of evolutionary ecology is that when a structural niche is filled, species diversification should either slow or come to an end due to competition. There must be some other way they are sharing that habitat to avoid competition,” he said.
The researchers hypothesized that the evolution of physiological traits related to temperature tolerance also facilitated the maintenance of biological diversity by providing an additional axis of co-existence.
Working with Alex Gunderson with the University of California at Berkeley and D. Luke Mahler with the University of Toronto, Leal set out to test this hypothesis. The team caught and collected thermal physiological data on over 300 anoles. Most of the anoles belonged to the Puerto Rican cristatellus group, which includes four pairs of sister species, each of which occupies a different thermal niche. They also included data on Jamaican anoles. The researchers measured two aspects of thermal physiology: maximum thermal tolerance and optimal temperature for sprint performance, which they used as a measure of fitness. They asked if a species heat tolerance correlated with its optimal sprint performance. They expected that sister species would diverge in one or both of these physiological traits.
They found that all Puerto Rican species pairs diverged in at least one of the two physiological traits. In three of the four pairs, the species that preferred the warmer environment had a higher thermal maximum temperature. In two cases, the species that preferred the warmer environment also had had a higher optimal temperature. They found a similar pattern among the Jamaican anoles.
“These findings show that when morphologically similar species co-occur in Puerto Rico and Jamaica, they differ in thermal physiology. We can say that thermal physiological differentiation is important for increasing local species richness,” said Leal.
An additional insight was that thermal physiology evolved slower than morphology. This evolutionary interplay, Leal said, has real-world implications when one considers the rate at which the world’s climate is warming.
“This is not good news for the ability of anoles to adapt to climate change,” said Leal. “The data suggest that the rate at which physiology changes in anoles is not fast enough to cope with how fast temperatures are rising.”
Stephen Colbert being bitten by a green anole
All is explained in the video below.
From article by Sater and Smith in March 2018 Herp. Review.
The March 2018 issue of Herpetological Review is chockful of fascinating Natural History Notes about anoles. Highlights: A male carolinensis mating with a female sagrei (we’ve seen that before!), a cristatellus eating a smaller member of the same species, a sagrei eating an anole, and communal nesting in green anoles. You can read all these stories and more, now that Natural History Notes are open access and downloadable! Click on volume 49(1), Natural History Notes.
