Although the A. carolinensis genome is not yet published, it is already being widely used in comparative genomic studies. In a very interesting talk, Matt Fujita reported on the GC content of the anole genome in comparison to other taxa, with special focus on bird and mammal genomes. It turns out that the anole genome differs in many interesting respects. One particular focus was on isochores, which are long stretches of the genome with high GC content. It turns out that the anole genome contains a substantially lower proportion of isochores, and that the distribution of GC content is much more homogeneous across the genome.
Category: New Research Page 62 of 66
In an impressive synthesis of previous (Cox and Calsbeek, 2010; Cox et al., 2011)
and new work, Bob Cox reported on studies examining the adaptive significance
of sex ratio variation in brown anoles. Previous lab studies had indicated that
when a female brown anole mates with a large male, she tends to produce sons,
whereas when she mates with a smaller male, she disproportionately produces
daughters. Cox and colleagues set out to test why that might be so by producing
offspring with known parents in the lab, and then releasing them into the wild. The idea was to test whether sons fathered by larger males survived better than sons produced by small males and, conversely, whether daughters from small males fared better. They tested a number of other hypotheses, namely that females in good condition produced males which survived better (the Trivers-Willard hypothesis); that condition of males should affect survival of offspring; and that early hatching lizards survived better (a hypothesis suggested by early iterations of the experiment).
The hypotheses were evaluated in two stages: whether offspring production was a function of parent phenotype, and whether offspring survival was related to parent phenotype.
The most strongly supported hypothesis was the initial one: female ability to link offspring sex with paternal phenotype appears adaptive; male offspring fathered by large males and females sired by small males have highest fitness. Other hypotheses were less variably supported: either the sex of the offspring was not related to the condition of the parent, or no survival advantage was found.
Anoles in Florida really have to deal with some strange neighbors. You just never know who is going to move in next door. Giant day geckos are rapidly expanding their range in the Fla Keys and use a variety of perch sites and heights including manmade structures. This of course brings them in contact with all species of Anolis occurring there. I enjoyed watching this interaction… The A.carolinensis/porcatus was really troubled with the invader, using the entire repertoire of his display skills. The gecko (Phelsuma grandis) which was at least three times the mass of the anole, only seemed slightly hesitant to continue to the crown of the tree. Once there the anole displayed for several minutes trying to influence the gecko out of his small palm. Perhaps one day they will learn each others language.
Lizard in an Evolutionary Tree's reworking of Williams' classic figure. Note that A. gundlachi is a trunk-ground anole, not, as indicated, a trunk-crown anole.
In this famous figure, Ernest Williams sketched out his view of how anole diversification occurred on the Greater Antilles, using Puerto Rico as an example. First, species diverge to use different structural habitat, producing the different ecomorphs. Subsequently, within-ecomorph divergence produces species that use the same structural habitat, but which occupy different climatic micro-climates, ranging from cool and moist rainforest to blazing hot and dry semi-desert. This two-stage pattern of evolution is displayed not only on Puerto Rico, but also on Cuba and Hispaniola (Jamaica, the most species deprived island, has little within ecomorph diversity).
In contrast to the plenitude of research in recent years on the adaptive basis of morphological differences among the ecomorphs, relatively little work has focused on the extent to which closely related species—members of the same ecomorph class—have adapted to occupying different microclimates.
AnoCar 2.0 is now fully integrated into the Ensembl and UCSC browsers, and NCBI’s Mapviewer. Click to view.
The March issue of IRCF Reptiles & Amphibians: Conservation and Natural History has just been received, and it is their most anoleful issue ever. The highlight is a delightful report of an expedition to tiny and desolate Sombrero Island in the northern Lesser Antilles, home to a population of A. gingivinus which, lacking trees as available perches, is forced to hang onto the vertical walls of the abandoned lighthouse keeper’s house.
In addition, another article reports the introduction of A. sagrei to St. Lucia, complementing introductions of that species to many other islands in the Lesser Antilles: St. Maarten, St. Vincent, Grenada and the Grenadines, and Barbados. Is it just a matter of time before it occupies every island south of the Greater Antilles? Another article, however, reports the snuffing out of a propagule of two A. sagrei that arrived to Layou, St. Vincent in a flower pot from Florida. However, as the article notes, the species thrives elsewhere on the island. Lastly, the Table of Contents page has a nice photograph of A. conspersus from Grand Cayman.
As if articles on anoles weren’t enough a reason to subscribe, I have to comment on the beautiful photographs that can be found throughout this magazine, along with interesting articles on a wide variety of reptiles and amphibians.
There are few topics more exciting than anole reproduction, but there’s still much we have to learn about the neuroendocrine mechanisms that allow these creatures to do the deed. We know that sex steroid hormones facilitate reproductive behaviors across a diversity of animals, and anoles are no exception. In particular, an enzyme called aromatase regulates both male and female sexual behaviors by synthesizing estradiol from testosterone. In a recent study using green anoles (Anolis carolinensis), Rachel Cohen and Juli Wade of Michigan State University examined whether lizard sex and season influenced the expression of aromatase in areas of the brain that are known to influence vertebrate reproductive behavior (the preoptic area (POA), the amygdala, and the ventromedial hypothalamus (VMH)).
- An egg of Anolis lionotus. Photo courtesy Edgardo Griffith.
One day, years ago, I was collecting data on the behavior of the Jamaican twig anole, A. valencienni. As I was watching a female, to my surprise, she entered a hole in a tree trunk, and then emerged a little while later. To my amazement, I then saw another valencienni do the same thing! Overcome with curiosity, I approached the tree, peered into the hole, and spied to my astonishment a large number of what seemed to be anole eggs. I was not aware that communal nesting—in which multiple females lay their eggs in the same place—is known in a number of anole species, including A. angusticeps, A. bartschi, A. lucius and A. valencienni. The seminal work on the subject is still Rand’s 1967 Herpetologica paper.
A recent paper adds another species to the list of known communal nesters, the first from Central America of which I’m aware.
In the pantheon of anoles, Anolis maynardi has a special place as one of the funniest looking species around. To the casual observer it appears that someone has taken an A. carolinensis (to which A. maynardi is closely related), grabbed it by the tip of the snout, and pulled it forward. The purpose of this pincer-like proboscis, much more extreme in males than in females (which are smaller), is unknown. Indeed, until recently, just about everything about the species was unknown.
Anolis maynardi is endemic to the tiny island of Little Cayman. Remarkably, although visible in the distance, the nearby island of Cayman Brac does not harbor the species. At least naturally. In 1987, A. maynardi was reported at the Cayman Brac airport, most likely a beachhead resulting from a stowaway on an island-hopping airplane. Another survey in 1991 still found it only near the airport, and nothing further was known.
- Photo from Partan et al. (2011)
For about a decade now, several researchers have used remarkably realistic looking robotic lizards to study lizard behavior. A pioneer in this approach—especially with regard to studying anoles—is Terry Ord, now at the University of New South Wales. You can see videos of his robotic lizards, as well as clips of a variety of anole species displaying, on the Terry Ord Channel on YouTube (or read about his most recent work here). As you’ll see, these robots are very realistic, both in terms of appearance and motion pattern—they bob, pushup, and extend their dewlap just like a real anole. In fact, even when the rubber body of the lizard hasn’t been attached, the underlying struts move in a clearly anole-like fashion. Bottom line, at a distance, I think most humans would be fooled by a displaying robo-anole. And lizards seem to be fooled, too, because they clearly respond by displaying and approaching the robot—check out the videos and/or Ord’s papers. Or read the recent paper by Partan et al., which demonstrates that A. sagrei responds more to a robot giving the typical signature display than to one presening a different display occasionally given by a lizard in the population.
Just like audio playbacks which revolutionized the study of bird vocal communication, robotic lizards provide the opportunity to rigorously examine lizard behavior in a controlled and replicated manner. Many different questions could be examined, but one of particular interest concerns how anoles distinguish conspecifics from heterospecifics. By altering the display pattern—the timing and amplitude of headbobs, pushups, and dewlap extensions—and by altering the color and pattern of the dewlap, researchers have the ability to understand species-recognition. In turn, such an understanding may provide critical insight into how new species arise, because speciation is the result of changes that lead individuals to no longer recognize each other as conspecifics.