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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.

Kristin Winchell’s research on Puerto Rican A. cristatellus evolution in cities is referred to in a nice piece in the New York Times by Menno Schilthuizen.

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.

We’ve seen anole wedding cakes and thesis defense cakes, but here’s a new one. Anole research veteran Natalie Jacewicz reports:

For my bachelorette party, my bridesmaids went to an erotic bakery (quite the business niche) in Boston and brought the shop pictures of Anolis lizards. The bakery evidently usually deals in, er, human encounters, so only had skin-toned frosting, and the store clerks weren’t sure if they could do anything lizard themed. But the shop owner evidently got really into the project, did a lot of independent anole research, and produced the cake below. Yes, that is a bridal veil on the yellow one.

Some weeks ago, a paper I wrote on the display behaviour and morphology of fan-throated lizards was published early online at the Journal of Herpetology. Some unfortunate timing meant that my paper did not incorporate these lizards’ new taxonomy, recently published by V. Deepak and colleagues. In this post, I’m going to summarize my results, and explore them in the context of what we now know about Sitana (Agamidae) systematics.

Male fan-throated lizards (surprise, surprise) have fans under their throats that are displayed in a manner analogous to the Anolis dewlap. The appearance of the throat-fan varies dramatically across this group, from small and mostly white to large and blue, black, and orange. I wanted to answer two broad questions

1. Does display behaviour vary with throat-fan morphology? In other words, if you have different tools with which to communicate, do you communicate differently?
2. Can we examine morphological and environmental variation to deduce anything about how this variation in throat-fan morphology has evolved?

Figure 1 from my paper, showing sampled sites and throat-fan variants.

To address these two questions, I measured the display behaviour, morphology, and environment of eight populations of lizards, from three “throat-fan variants.” I found the following:

1. The main axis of variation in display behaviour differed between the coloured-fan variant and everybody else. Displays were fewer and longer in the coloured-fan variant, and included more head twists. The same axis of display behaviour did not differ between the white-fan and the intermediate-fan variants, though there was variation in the frequency of head-bobs across populations with different-sized throat-fans. These differences in display behaviour make sense in light of morphology. Head twisting was more frequent in the variant with a large blue section on the throat-fan that appears iridescent. Head-bobs, which often co-occur with a fully extended throat-fan, were more frequent in the variant(s) with smaller throat-fans (see Figure 6 in my paper for more).
2. Throat-fan elaboration (both size and colour) was paired with increased male-biased sexual size dimorphism, suggesting sexual selection as a likely selective force driving throat-fan variation.
3. Habitat structure did not co-vary with throat-fan morphology, suggesting that the visual environment is unlikely to play much of a role in the maintenance of this variation in throat-fan morphology. But because these lizards all persist in human-modified landscapes, it is difficult to discern how important the visual environment was for the origin of dewlap diversification in this group.

Figure 2 from Deepak et al. 2016.

Based on geography, I can tell that all three of the coloured-fan variant populations I sampled belong to the newly described Sarada darwinii. The white-fan populations are Sitana laticeps and Sitana spinaecephalus (+ one population I’m not sure about), and the northern and southern intermediate-fan populations are Sitana ponticeriana and Sitana visiri respectively. Recast in terms of these species delimitations, I found that:

1. Display behaviour differs between the genera Sitana and Sarada. It doesn’t vary consistently with species within Sitana, though variation in head-bobbing should be explored further.
2. There are two broad possibilities for throat-fan evolution in the group. One possibility is that throat-fan elaboration and a shift towards male-biased SSD has evolved independently twice, once in Sarada (Clade 1) and once in the South India/Sri Lanka clade (Clade 3 in the phylogeny) in Sitana. The other possibility is the reduction of dewlap size and colour in the west Indian Sitana clade (Clade 2). This question won’t be definitively answerable until we have a phylogeny that includes the remaining north-eastern species of Sitana as well as more species of the sister genus Otocryptis, which also vary in the presence and morphology of the throat-fan.

Before knowing about the phylogeny, I predicted that throat-fan elaboration had evolved twice in fan-throated lizards, based on a suite of differences between the coloured-fan variant (now Sarada) and the intermediate-fan variant (now Sitana Clade 3). The main ones are:

1. Different display behaviour.
2. Different allometric relationships between body size and throat-fan size, suggesting different ways in which throat-fans have gotten big.
3. Different spectral reflectances from the blue and orange patches, plus the presence/absence of black on the throat-fan.
4. The ability of Sitana, but not Sarada, to turn “on” and “off” the blue colour on their throat-fans (more about this in a future post!).

These differences now lead me to favour the first of the two possibilities outlined above: repeated, somewhat parallel evolution of throat-fan elaboration, as opposed to the loss of an elaborate throat-fan. Given that the sister genus Otocryptis has also either evolved or lost a throat-fan (throat-fans are present in O. nigristima and O. wiegmanni but not O. beddomi), this group is positively rife with lability in display evolution, offering all sorts of exciting possibilities for future research!

Anolis garmani. Photo by Janson Jones.

Over on phostracks.com: Florida Wildlife, Ecology and More, Janson Jones reports on a very successful trip to Miami that yielded many anoles, most notably the Jamaican crown-giant, Anolis garmani and the Cuban knight anole, Anolis equestris.

Photo by Janson Jones.

Photo by Janson Jones

Janson Jones is at it again. Actually, he’s been at it for a year, but somehow that slipped below our radar. The former purveyor of Dust Tracks on the Web has a new venue, phosTracks.com: florida wildlife, ecology and more.

Like it’s predecessor, phosTracks is full of keen natural history, engagingly presented and complemented by gorgeous photography. And better yet, anoles are one of Jones’ two favorite animals, neck-and-neck (hard as it may be to believe) with watersnakes.

Check out some of Jones’ recent musings on:

curly-tailed lizards:

Photo by Janson Jones

red-headed agamas:

Photo by Janson Jones

Anolis cristatellus:

Photo by Janson Jones

and more! Stay on these pages for some of his giant anole goodness coming up soon!