Author: Jonathan Losos Page 37 of 130

Leo Fleishman and colleagues have just published a cool paper in Functional Ecology, “Why do Anolis dewlaps glow? An analysis of a translucent visual signal.” Co-author Manuel Leal provides the back-story on how the paper–which he refers to as “experimental natural history”–came to be in his lab’s blog, Chipojo lab.

And the New Scientist provides a nice summary of the article in its post: ”

Luminous lizard lotharios ahoy! In the dark undergrowth of the forest, it’s not easy to be seen. Male Anolis lizards use colourful throat fans, called dewlaps, to woo females as well as ward off rivals and predators. But one species has a neat trick to make itself stand out even more – it uses an optical illusion to make its dewlap appear to glow.

The dewlaps are translucent, which means they can transmit as well as reflect light. However, because most objects in the lizards’ environment – such as rocks and tree trunks – simply reflect light, our eyes “expect” them all to appear relatively dull. By transmitting light from the background, the dewlap tricks our eyes – and the eyes of other lizards – into thinking it is actually a light source, says Leo J. Fleishman of Union College in Schenectady, New York, who has studied the lizards for years.

Fleishman’s team was curious to find out why the trick evolved – was the glowing dewlap a way to increase contrast with darker backgrounds or a way to make its colour clearer?

To explore the issue, Fleishman’s team examined the photoreceptors in the lizard’s eyes to work out how they would view the dewlaps. They found that the glow did not create more contrast with the background, which naturally contains other bright spots – where a patch of sunlight passes through the vegetation, for instance. But the glow did significantly reduce the visual overlap, as the lizard’s eyes would experience it, between the throat fans and the colours of natural backgrounds.

The glowing dewlap may be more common than we think. Only a few of some 400 species of Anolis lizards are known to carry the trait, but Fleishman has seen photos suggesting other species’ dewlaps might glow too.

“My guess is that the phenomenon will turn out to be widespread once people start looking, but very few people have looked,” he says.

Here’s the paper’s summary:

Summary

It’s been a good couple of weeks for herps-in-amber fans. Last week, Emma Sherratt and colleagues (including me) published a paper expanding the number of known Dominican amber anoles from 3 to 38. And now comes a paper by Poinar and Wake in the journal Palaeodiversity reporting a finding perhaps even more improbable: a fossil salamander in amber from the Dominican Republic.

What is so remarkable about this discovery is that salamanders do not occur anywhere in the Caribbean today. Indeed, salamanders are one of the textbook examples of taxa thought to be unable to disperse overwater, leading to what used to be called “disharmonic faunas”–islands that are missing some elements normally found on the mainland.

Detailed analysis indicates that the specimen is a member of the Plethodontidae, the family to which all neotropical salamanders belong. How did it get to Hispaniola? One possibility is that it hopped onto the proto-Antillean landmass as it passed by and perhaps came into contact with the continental Americas around 70 million years ago. Some hold that anoles got to the islands in the same way, though molecular data suggest that anoles are too young for vicariance to explain their occurrence in the Caribbean. The alternative possibility is that salamanders got to islands the old-fashioned way, by floating on flotsam and jetsam. Sensitive to dessication, most amphibians–and plethodontids in particular–wouldn’t seem good candidates for overwater dispersal, but stranger things have happened.

Regardless of how they got there, the presence of salamanders in the Caribbean twenty million years ago is a surprising finding adding a new dimension to our understanding of Caribbean biogeography.

A little while ago, Alexis Harrison asked why there were so few anole talks at the ASIH meeting in Reno. Now we know the reason–they’re all at the SSAR meeting in Lawrence, Kansas, which began today. In total, there are 13 anole presentations (talks plus posters). You can find them in the Meeting Program (also available at meeting website)–just search for “anol”  (11) or “Norops” (2).

At the moment, we have no one lined up to provide first-hand reports from the meeting. If any readers out there are at the meeting and want to report in, we’d very much appreciate it!

While no one was looking, AA welcome it’s one millionth page view last Thursday, four years in the making. Here’s to the next million!

Introducing Platysaurus attenboroughi

David Attenborough, fascinated by flat lizards.

Martin Whiting’s lab at the University of Macquarie has been very busy of late. In a single day, I received notice of two new, fascinating papers.

First, Whiting and colleagues described a gorgeous new species of flat lizard (Platysaurus) after Sir David Attenborough. Enough said. Read all about it in Zootaxa or on the Whiting Lab website, The LIzard Lab.

The second paper, available online in Biological Journal of the Linnean Society, concerns a topic near and dear to Anole Annals: lizards with projections on their noses. We’re particularly hung up on horns (1,2), but some species have rostral blobs. Like the Sri Lankan Ceratophora tennentii. Whiting and colleagues examined this species, finding very little difference between the sexes, although males did have longer heads and bigger nasal projections. However, bite force did not correlate with nose size. What’s going on with the rostral appendages, as well as the color on the throat. labials, and inside the mouth, is unknown. A fascinating lizard worth more study!

Here’s the paper’s abstract:

Measures of physiological performance capacity, such as bite force, form the functional basis of sexual selection. Information about fighting ability may be conveyed through a structural feature such as a rostrum (i.e. horn) or a colour signal and thereby help reduce costly conflict. We quantified sexual dimorphism in key traits likely to be the targets of sexual selection in Tennent’s leaf-nosed lizard (Ceratophora tennentii) from Sri Lanka, and examined their relationship to bite force and body condition. We found body length and bite force to be similar for males and females. However, head length was significantly greater in males and they had significantly more conspicuous throats and labials (chromatic contrast and luminance) than females. Males also had a proportionally larger rostrum, which we predicted could be an important source of information about male quality for both sexes. Rostrum length was correlated with throat chromatic contrast in males but not females. Nonetheless, the rostrum and aspects of coloration did not correlate with bite force or body condition as we predicted. We have no information on contest escalation in this species but if they rarely bite, as suggested by a lack of difference in bite force between males and females, then bite force and any associated signals would not be a target of selection. Finally, males and females had similar spectral reflectance of the mouth and tongue and both had a peak in the ultra-violet, and were conspicuous to birds. Lizards only gaped their mouths during capture and not when threatened by a potential predator (hand waving). We hypothesize that conspicuous mouth colour may act as a deimatic signal, startling a potential predator, although this will need careful experimental testing in the future.

AA‘s correspondent in the West Coast Bureau, Alexis Harrison, just filed this report from Reno:

At the Joint Meeting of Ichthyologists and Herpetologists in Reno, Nevada this week, the most surprising news for an anolologist may be the lack of presentations focusing on anoles. Given the ubiquity of anoles in ecology and evolutionary studies, I’ve come to expect a steady stream of anole presentations and posters, anole discussions, anole-themed paraphernalia and other anole-centric events. Maybe I’ve been living too much in an anole-shaped bubble.

The sole anole-focused talk was a presentation by Kirsten Nicholson (with co-authors Craig Guyer and John Phillips) entitled “Biogeography of Central American anoles in the genus Norops”. In this talk, Nicholson et al. explore biogeographic hypotheses developed in their 2012 paper in greater detail, with a particular focus on the timing and geographic context of diversification in the Norops clade. Current and ongoing work incorporates the addition of several new species and greater sampling of widespread species into the phylogeny. Although the results presented were preliminary (mitochondrial sequences are already available, with nuclear sequence data to come), the broad patterns in the data appear to be consistent with the conclusions from the 2012 paper: the estimated divergence times among three subclades of the Norops group are ancient, in the range of 40-50mya, while a reconstruction of the ancestral range of the Norops group suggests an early colonization of South America followed by re-expansion northward and then back south.

Regular readers of Anole Annals will probably remember the vigorous debate occasioned by the publication of Nicholson et al 2012. Based on this latest research, I think we can expect further provocative papers and ensuing discussion in the near future. Let’s hope this will stimulate more Anolis talks at next years JMIH meeting in New Orleans!

Anlolis meridionalis. Photo from the Reptile Database

Recently, Kristin Winchell reported on the 2015 Evolution meetings in Guarujá,  Brazil.  Kristin noted: “Fernanda de Pinho Werneck gave a lightning talk titled “Cryptic lineages and diversification of an endemic Anole lizard (Squamata, Dactyloidae) of the Cerrado hotspot” that I am sad to have missed. If anyone did catch it, please let us know in the comments.”

Well, Fernanda herself responded and summarized her talk: “Hi Kristin, really cool summary of the Anole talks! Here is what I presented at the meetings for Norops meridionalis lighting talk: we found five highly divergent lineages, confirmed by multiple phylogenetic and species delimitation methods. These lineages (potential candidate species) diverged in the early-mid Miocene, when most of the geophysical activity of the Cerrado took place. Population-level analysis for the broader distributed lineages showed evidence for non-stationary isolation by distance, when the rate at which genetic differentiation between individuals accumulates with distance depends on space. Finally, niche conservatism, rather than niche divergence, seems to be the main mechanism that promoted the fragmentation of main populations across the Cerrado. Cheers!”

Fernanda also pointed out that the work is the basis of a paper by Carlos Guarnizo et al. that is in revision at Molecular Phylogenetics and Evolution. We’ll hear more when the paper appears!

Researchers have previously shown that anoles and other lizards will respond to moving robot lizards. In a recent elegant study in Herpetologica, Joe Macedonia and colleagues have used such robots to investigate what aspects of a lizard’s body or behavior are most important in eliciting responses. The work was conducted in Bermuda, where A. grahami and A. extremus were introduced from Jamaica and Barbados, respectively, in the first half of the last century.

Macedonia and team built robots to look like these two species. It’s worth reading the details of how they built these realistic looking models: “We constructed a conspecific robot body and dewlap to resemble our study species, A. grahami, as well as a heterospecific robot body and dewlap to resemble A. extremus. Excluding the hind limbs and tail of each robot, which were made of airbrushed latex cast from lizard specimens (see Macedonia et al. 2013), each robot body was carved from a thick wooden dowel and attached to a servomotor pushrod. Anterior to the hind limbs, robots were covered with an image created in Adobe PhotoshopH from photos of the study species (Fig. 1). These images were mirrored and joined together at the body midline. Final images were printed onto adhesive-backed fabric and molded around the wooden body, which, together with the latex hindquarters, was attached to the polyvinyl chloride (PVC) perch. Dewlaps were fashioned from white, semitransparent guitar picks that fit into a slot carved in the neck of the robot body. A small hole that was drilled into the guitar pick was secured to a hinge pin that allowed it to pivot and extend. A second small hole in the pick allowed insertion of a thin wire that was attached to the pushrod, which in turn was attached to a servomotor.” The researchers were able to tune two servomotors to produce dewlap extension  and head-bobbing patterns similar to those produced by each species. The following movies illustrate what the robots looked like.

In the first experiment, wild A. grahami were presented with robots in the following four treatments: grahami color and grahami display patterns; grahami color and extremus display patterns; extremus color and grahami display patterns; and extremus color and display patterns.

Sixty-seven of 145 lizards responded to the displaying robots, and the strongest response was to the normal-looking grahami. In addition, the lizards dewlapped more to the robot with grahami color but extremus display pattern than they did to either of the robot treatments with extremus coloration; however, in terms of head-bobbing, the grahami did not distinguish between the three other treatments, responding similarly to all three at a lower headbobbing rate than to the normal- looking and behaving grahami robot.

In a second experiment, wild grahami were exposed to robots that looked like grahami  and that: bobbed and dewlapped; only bobbed; or only dewlapped. Unexpectedly, they dewlapped the most to the robots that only dewlapped, and headbobbed the most to the robots that only headbobbed.

Macedonia et al. conclude the paper by suggesting that in the future, the best way to further this line of research will be to develop robots that can be controlled in real-time such that the robot’s behavior can be responsive to what the subject lizard does.

I suppose we should be glad that Antiguan racer is back from the brink of extinction, even if it’s bad news for this Antiguan anole.

An article in Oryx recently trumpeted the successful elimination of rats and mongooses from the 15th Antiguan offshore island. Once these invasive depredators have been removed, local species, including the endangered Antiguan racer have thrived, increasing in population over the last 20 years from ca. 50 to over 1,000. Though not endangered, anoles have benefited as well, with three-fold higher densities on islands on which the invaders have been removed compared to those on which they remain.

Photo by Manuel Leal in the New York Times

The New York Times yesterday had a long article on Manuel Leal’s research on the homing ability of Anolis gundlachi. Manuel has discovered that if you catch a gundlachi and let it go somewhere else in the forest, it will very quickly find its way back to its tree. He’s done a number of experiments to see if they’re using magnetic sense, polarizing light or telepathy (ok, maybe not the last one), but so far has been unable to figure out how they manage to get home. In fact, as the article states, he’s looking for suggestions. Read the article and give him such much-needed help!