A year ago, McCranie and Kohler published The Anoles of Honduras: Systematics, Distribution, and Conservation (available on Amazon for under twenty bucks and downloadable for free on the Museum of Comparative Zoology website).
In case you missed them, we thought we’d provide copies of some recent reviews of the book–in the last year, two favorable book reviews have appeared by Levi Gray in Herpetological Review and by Steve Poe in Quarterly Review of Biology.
Anolis sagrei
From time to time, people find anoles with broken dewlaps. Here’s an extreme example, found by Bob Powell and Rich Sajdak on the island of Grenada. Years ago, Richard Tokarz reported a lab study that showed that males with non-functional dewlaps mated as frequently as intact males, and a follow-up study with Ann Paterson and Steve McMann showed no difference in the field between males with and without working dewlaps. Makes you wonder what the dewlap is needed for.
Bob points out that brown anoles have spread widely in disturbed lowland habitats since first discovered on Grenada in 2002, when they were restricted to intensely disturbed urban habitats and decorative plantings in a few resorts.
All evolutionary biologists are familiar with Robert Trivers, but many do not know that some of his most important work was conducted on Anolis lizards. This work–as well as the rest of Trivers’ life–is featured in his just-published memoirs, Wild Life: Adventures of an Evolutionary Biologist. I had the good fortune to review the book for Current Biology. You can read my review, but the short story is: a fascinating book about one of the great figures–and characters–of modern evolutionary biology. And in case you’re wondering, it was the publishers who put a collared lizard, instead of an anole, on the cover. Available on Amazon for $12.99!
Remarkably little is known about the natural history of the Puerto Rican twig anole, Anolis occultus, except where it sleeps. The reason is simple: the
animal is small, moves slowly, is highly cryptic and probably spends a lot of its time amidst the twigs high in the canopy. As a result, there have been reports of only a handful of animals located while they are active.
In a just published paper, Ríos-López and colleagues report two new observations of these charming little lizards, one of nectarivory (above) and the other, sadly, of predation by a kingbird (right). In addition, the paper presents a comprehensive review of what we know about this species and its conservation prospects.
Not a dewlap? Photo by Morley Read.
In a recent paper, Hagman and Ord discussed how dewlaps have evolved multiple times, often with different underlying anatomy. This is an excellent paper, but I was intrigued that Polychrus, sometimes considered the sister taxon to anoles, in part because of its apparently anole-like dewlap (see above), was not considered to have a dewlap.
I wrote Terry Ord, asking “I didn’t understand one thing. You seem to say there is no evidence for extendible dewlaps in several species of Polychrus, but a quick Google reveals plenty of images of these species with dewlaps extended. I take your point in the previous sentence that actual observations of the dewlap being used are rare, but did you really mean to say that they don’t exist at all?”
Terry responded: “What I found when attempting the first paper of this series (Ord et al. 2015, Journal of Evolutionary Biology) is that relying on photos alone is really problematic for identifying a moveable dewlap (a.k.a., a dewlap like anoles or Draco or Sitana).
For example, if you google Sceloporus — who definitely don’t have dewlaps — you’ll find photos where species do appear to have something like a small dewlap. In fact, I found an image of what was clearly a Sceloporus that looked to have an engorged throat that was remarkably similar to your Polychrus photo… All the google images I’ve found so far that are obviously Polychrus (and not anoles) could quite easily be engorged throats akin to Sceloporus and other non-dewlaped iguanids/agamids.
But the clincher for me is that all the hyoids we’ve looked at so far for both Sceloporus and multiple species of Polychrus (and other non-dewlaped iguanids/agamids) all look very similar (e.g., see Fig 5a in the JEB paper and supplementary info). The point being, the mechanics of the hyoid simply isn’t functional in the capacity of extending a dewlap like in anoles and others.
Of course, while the mechanics of the hyoid in extending the dewlap in anoles is well described, how Draco do it and some other genera is unclear. I’m hoping someone will look into detail on the biomechanics of the dewlap extension in non-anole groups because it can clearly be very different to anoles — e.g., the attachment points for key muscles for the anole dewlap are absent in Draco, so they’re sticking that dewlap out using a very different mechanism. Regardless, there are still key signs in the hyoid that point to a moveable dewlap in Draco (and other genera) that are not present in Polychrus.
Proof of a Polychrus dewlap would have to be a video of a Polychrus extending the dewlap because videos of Sceloporus quickly reveal that its an engorging (“puffing”) of the throat, so direct observation is a solid alternative to looking at the hyoid.
The taxonomy of “Polychrus” is potentially sketchy and not all species really are of that genus. Which means I also wouldn’t be surprised to see a species that has been classified Polychrus, but really isn’t related to all the Polychrus species we’ve examined the hyoids of, actually having a convincing moveable dewlap.
But at the moment, Polychrus = a moveable dewlap, all the evidence says otherwise. I also wonder whether the historical association of Polychrus as basal to anoles resulted in reaffirming wishful thinking field observations into the current myth.”
Terry’s next email made the distinction clear (as well as his unwarranted agama-philia): “If your notion of a dewlap is a prominent ornament that is dynamic in some sense (becomes extended through puffing out the hyoid in general or pushing out the CII in particular), then there are many many examples in agamids, and a handful in iguanids. I would definitely include Sceloporus, too.
If your notion of a dewlap is more specific to something that is part of a complex behaviojral display and involves rapid extension of a structure that is complex in temporal and amplitude characteristics, then it’s basically anoles, Sitana/Otocryptis, Draco and possibly one or two other agamids.
Agamids still clinch the diversity stacks in all regards – ha!”
Also not a dewlap
Tail successfully regenerated.
Abstract
Lizards are amniotes with the remarkable ability to regenerate amputated tails. The early regenerated lizard tail forms a blastema, and the regenerated skeleton consists of a cartilage tube (CT) surrounding the regenerated spinal cord. The proximal CT undergoes hypertrophy and ossifies, while the distal CT resists ossification for the lifetime of the lizard. We hypothesize that differences in cell sources and signaling account for divergent cartilage development between proximal and distal CT regions. Exogenous spinal cord implants induced ectopic CT formation in lizard (Anolis carolinensis) blastemas. Regenerated spinal cords expressed Shh, and cyclopamine inhibited CT induction. Blastemas containing vertebrae with intact spinal cords formed CTs with proximal hypertrophic regions and distal non-hypertrophic regions, while removal of spinal cords resulted in formation of proximal CT areas only. In fate mapping studies, FITC-labelled vertebra periosteal cells were detected in proximal, but not distal, CT areas. Conversely, FITC-labelled blastema cells were restricted to distal CT regions. Proximal cartilage formation was inhibited by removal of periosteum and could be recapitulated in vitro by periosteal cells treated with Ihh and BMP-2. These findings suggest that proximal CTs are directly derived from vertebra periosteal cells in response to BMP and Ihh signaling, while distal CTs form from blastema cells in response to Shh signals from regenerated spinal cords. Thus, lizard tail proximal CTs develop independently from tail blastemas, resembling cartilage calluses formed during fracture repair, while distal CTs are derived from the blastemas similar to regenerated salamander tails.
Different phenotypic forms often serve the same functional outcome. A classical textbook example is the evolution of the wing in dinosaurs, birds and bats. This implies that organisms can respond in a variety of comparable ways to selection and that the same selection pressure thus can produce phenotypic diversity. Terry Ord and I have an early view paper in the American Naturalist that shows that an anole-like dewlap has evolved repeatedly in iguanids (Anolis) and agamids (Draco, Sitana, and Otocryptis), but in each case through different modifications to the underlying hyoid, which is the structure that powers the extension of the dewlap. The main point of difference among hyoid morpho-types, and also the component critical for the evolution of an extendible dewlap, is the angle between a short perpendicular structure called the hypohyal (see the figure) and a longer structure called the second ceratobranchial, which runs along the edge of the extended dewlap. There is also significant variation in the relative lengths of the same structures.
Other lizard species have converged around other hyoid morpho-types (our analysis identified a total of eight separate hyoid morpho-types). Interestingly we found evidence for convergence in hyoid morphology among species from distantly related genera, such as Polychrus, Gonocephalus and Trapelus. Species from these genera lack the large dewlap type found in Anolis and Draco, although the hyoid morpho-type of the two groups show some gross similarities. We suggest that the hyoid morpho-type of Polychrus, Gonocephalus and Trapelus might represent what an intermediate step looks like in the evolution of an extendable dewlap. More generally, our study shows that multiple adaptive solutions have been possible in apparent response to a common selection pressure, and that the phenotypic outcome that subsequently evolved in different genera seems to have been contingent on the history of the group in question.
And an Ecuadorian student has studied the use of their horns in intraspecific interactions. Read all about it on BBC Earth.
Powered by WordPress & Theme by Anders Norén
