Photo by Karen Cusick
Karen Cusick recounts this scary encounter on Daffodil’s Photo Blog. The green turned around, to face its impending doom head on.
Photo by Karen Cusick
And then….
Category: All Posts Page 91 of 148
In a recent paper in Life: the Excitement of Biology, Ríos-López et al. report observations of predation on a variety of Puerto Rican lizards. Iguanas and Ameiva suffer much of the brunt of predation (including a beagle with a juvenile iguana in its mouth), but reports include A. cristatellus eating both A. pulchellus and A. stratulus (which was subsequently regurgitated–perhaps because it was too large?–and immediately devoured by an Ameiva that ran up to the fallen carcass). In addition, a tody (above) brought an anole back to its nest.
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
- Male anoline lizards utilize a colourful, expandable throat fan, called the dewlap, to rapidly and unambiguously signal their presence and species identity to conspecifics. Under some viewing conditions, the dewlaps of some species appear to glow vividly, because they transmit a great deal of diffuse light, creating a translucent signal. Translucent signals are probably found in many animal groups, but they have rarely been studied.
- We hypothesized that dewlap translucence might (i) increase dewlap/background luminance contrast or (ii) increase the reliability of the colour as a species recognition signal by lowering the colour discrimination threshold in low light conditions such as forest shade.
- We calculated dewlap colour (spectral radiance) for the Jamaican lizard Anolis lineatopus at natural perch sites with, and without, the inclusion of transmitted light.
- Transmitted light did not significantly increase the magnitude of luminance contrast between the dewlap and background.
- We plotted colours of dewlaps, background patches of habitat and dewlaps of sympatric species in an anoline perceptual colour space (the colour tetrahedron), based on the four classes of cone photoreceptors found in the retina. Using a newly developed approach, we used ellipsoidal plots of uncertainty to quantify perceptual overlap between dewlap spectral radiance and values for natural distractor colours. Diffuse transmission of light through the dewlap greatly reduced the perceptual overlap between the dewlap and natural background colours.
- This finding strongly suggests that selection has favoured the evolution of a translucent dewlap as a mechanism to increase the reliability of detection of the signal under the low light conditions. In general, any animal’s colour signal must emit sufficient light intensity to allow the colour to be discriminated from other distractor colours in the habitat. This will tend to favour the evolution of colours with higher total intensity (i.e. higher reflectance and/or transmittance) in animals that signal in relatively low light conditions such as forest shade.
Anthony and Kevin near the golf cart. This inland forest was the tallest we could get access to on the island.
A July trip to the Bahamas to sample Anolis sagrei has been documented in recent posts by Graham Reynolds and Kevin Aviles-Rodriguez. During that trip, Kevin, Anthony Geneva, and I traveled to the island of Rum Cay to collect data on anoles. With a human population of fewer than 50 clustered in an around the southeastern town of Port Nelson, Rum Cay is mostly uninhabited. Access to a majority of the island’s 30 square miles is facilitated by narrow dirt roads, several of which, particularly those on the western half of the island, are overgrown and unnavigable. Our golf cart, well-equipped with off-road tires, was pushed to its limits as we strove to find lizards across several habitat types on the island.
L. loxogrammus on Rum Cay. Photo by Anthony Geneva.
Anolis sagrei was abundant among most of the island’s vegetation including forests, mangroves, and beach scrub. Their mostly red dewlaps appear similar to those we saw on nearby Long Island. In each habitat, the lizards were usually perched within 1 meter of the ground but were occasionally found on the ground or perched higher than 1 meter. One exception was a shrubby forest located at (23.66501, -74.868245) which contained abundant A. sagrei along with incredibly high densities of the San Salvador curlytail lizard, Leiocephalus loxogrammus. Here we didn’t see any A. sagrei on the ground despite being present at the site for several hours on two separate days. Not an easy place to get to, but it would be a great site for studying curlytail behavior and interactions between curlytails and anoles. In our adventures we also encountered several Anolis distichus, with more on that to come in a later post.
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.
Recently I was on Long Island alongside Graham and his team capturing Anolis sagrei. For our last night survey, we collected female lizards from a beach scrub habitat in McKanns (23.38831, -75.1408). During such a survey, we used headlamps to search for sleeping lizards perched on branches and leaves. At other sites we frequently found lizards on vegetation along the trails. At McKanns, land hermit crabs (Coenobita spp.) were congregated in high numbers on such vegetation. We seldom found lizards perching on plants where hermit crabs congregated.
Land hermit crabs (Coenobita spp.) active at night. Photo by Alberto Puente
Most lizards perched further away from the trail on the broad leaves of Cocoloba uvifera where hermit crabs were seen less abundantly. Perhaps due to their large numbers and the fact that they were active at night, land hermit crabs might be occupying perches that would otherwise be used by Anolis sagrei.
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!