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Along with Devi Stuart-Fox, Indraneil Das and Terry Ord, I recently published a paper in Biology Letters showing that arboreal Draco sumatranus lizards orient themselves on the tree trunk perpendicular to the position of the sun during broadcast signalling. This presumably increases the radiance of the translucent dewlap, and likely it’s conspicuousness.

Figure 1. (a) Draco sumatranus male displaying, showing the transmission of sunlight through the dewlap (photo: T. J. Ord). (b) Perch angle for displaying males, and (c) perch angle for non-displaying males, measured in relation to the sun. Both perpendicular angles (90° and 270°) have been transformed to equal 180°.

Draco lizards are ecologically analogous to the anoles and share similar signalling behaviour (see this recent Draco clip from the BBC’s Planet Earth II). They too possess extendable dewlaps that differ in colour and size between sex / species groups, and they also live in many different habitat types throughout Southeast Asia. I’ve written about my Draco research on Anole Annals before, here and here, if you’re interested – I hope they’re now well accepted as honorary anoles!

Like the anoles, the skin of the dewlap for many Draco species is stretched thin when extended and allows light to pass through.  Leo Fleishman published a Functional Ecology paper in 2015 measuring how the dewlap of Anolis lineatopis appears to glow when positioned with the sun behind them, and how this might improve signalling efficacy. Contrary to expectation, they found the transmission of light through the dewlap doesn’t improve the luminance contrast of the dewlap against the background. The radiance of the dewlap is increased by light transmission (radiance is the sum of the light reflected by the dewlap and any transmitted through the dewlap) – but patches of high radiance are very common in Anolis lineatopis forest shade environment, due to many the little shafts of light shining between gaps in the leaves. Instead they showed that due to the higher total intensity of the dewlap colour (thanks to light transmission) it’s probably easier for a conspecific to discriminate the signal from the natural background colours.

Given this and the similarity between anole and Draco dewlaps, I wondered whether Draco lizards might behaviourally adapt their position on the trunk relative to the position of the sun, to maximise the exposure of the extended dewlap to sunlight. To look at this, I just observed the position of the lizard relative to the sun upon first sighting, and noted whether the lizard was displaying, and if so, whether was it directly to a neighbouring conspecific, or whether it was a territorial broadcast display. We found males were significantly more likely to be oriented perpendicular to the sun when displaying, but not when not displaying (fig. 1).

Of course, signals intended for specific individuals in close-range encounters require the signaller to position themselves such that the receiver is in line of sight – but Draco lizards (and anoles) also give these ‘broadcast signals’ which are not intended for any specific individual, but just as territorial display. For these signals, where there is not another lizard around, they seem to orient themselves perpendicular to the sun, so their extended dewlap is exposed to the most light.

Female D. sumatranus also have dewlaps, but they are small in size and females only very occasionally engage in broadcast display.  I had not expected to see this orientation behaviour in females, as their dewlaps appear opaque and so don’t benefit from light transmission. However, I found the same orientation pattern for females as for males: perpendicular to the sun when displaying, but not when not displaying. This is perhaps because their dewlap reflects UV light (fig. 2) and direct sunlight is richer in UV and shorter wavelengths than light reflected off objects in the surrounding scene. Males have yellow dewlaps, and they too reflect a little UV (though much less than females). Of course, the transmission of light is unidirectional and only increases the radiance of the dewlap for those viewing the dewlap from the opposite side to that of illumination, so the benefit of direct sunlight hitting the UV/yellow male dewlap likely plays a role in this orientation behaviour for males as well.

Figure 2. a) Draco sumatranus male yellow dewlap colour reflectance;
(b) Draco sumatranus female blue dewlap colour reflectance.

What a lovely festive (a.k.a., brown) anole!

For more on the new AMNH exhibit on Cuba, see our previous report.

h/t to Sandra Buckner for notifying us of this magazine cover.

It’s been a while since we updated this montage…and at least a few months since the last anole cover. Get to work, everyone! And let me know if we’ve missed any.

Peter Uetz of the Reptile Database fame sends the following Valentine’s Day greetings:

If you or your significant other loves anoles, you may want to show her/him this hearty Anolis distichus (Figure 2960, above) on occasion of today’s Valentine’s Day. It clearly shows a heart on it’s head. Some other specimens such as the couple in Figure 3297 (right, from locality 1 in the Google map), also show a heart although it’s not as pronounced. Also note their blunt coloration which doesn’t seem to affect their affection.

Anolis distichus is pretty variable and even within this subspecies, A. d. dominicensis Reinhardt & Lütken 1863, to which all these specimen belong, there is considerable variation. By the way, the guy with the heart (Figure 2960) is from the same locality 3 as two other specimens which do not have a heart (Figures 2948 and 2968) although they display a similar shape on their heads. Figure 3087 shows yet another specimen for comparison, this time from locality 2.

2968

2948

3087

Various authors have described a dozen subspecies from Hispaniola (reviewed in Schwartz 1971, see map 2 from that paper). The northern half of Hispaniola is almost entirely in the hands of A. d. dominicensis, hence the specimens on the photos have been assigned to that subspecies.

Note that Glor & Laport 2012 elevated several Dominican subspecies of A. distichus to full species level, namely A. dominicensis, A. favillarum, A. ignigularis, A. properus, and A. ravitergum. The Reptile Database hasn’t followed this yet because their geographic sampling was limited to relatively few localities and they did not provide any updated diagnoses (but their recommendations have been recorded in the database). Also, there seems to be hybridization among several of these populations.

Photo localities:

2948: 3

2960: 3

2968: 3

3087: 2

3297: 1

Acknowledgments

Thanks to Miguel Landestoy and Luke Mahler who helped with the IDs.

References

Glor, Richard E.; Robert G. Laport 2012. Are subspecies of Anolis lizards that differ in dewlap color and pattern also genetically distinct? A mitochondrial analysis. Molecular Phylogenetics and Evolution 64 (2): 255-260.   http://www.sciencedirect.com/science/article/pii/S1055790310004276

Schwartz, A. 1968. Geographic variation in Anolis distichus Cope (Lacertilia, Iguanidae) in the Bahama Islands and Hispaniola. Bull. Mus. comp. Zool. Harvard 137 (2): 255- 309.  http://biodiversitylibrary.org/page/4784182

Schwartz, A. 1971. Anolis distichus. Catalogue of American Amphibians and Reptiles (108)

(used to be available online at ZenScientist, and maybe soon at the SSAR website again).

Anolis distichus in the Reptile Database

http://reptile-database.reptarium.cz//species?genus=Anolis&species=distichus

(an extended synonymy and distribution section will appear in the next database release)

The database entry also has another 43 references most of which are available online.

Any congress advertising with a horned anole (Anolis proboscis) must be worth attending. Check out the details at the conference website.

A new paper in Zootaxa aims to figure it out, based on the travel journals of its describer, Franz Werner. Here’s the paper’s abstract:

The eminent Austrian zoologist Franz Werner described several new species of amphibians and reptiles from America, including Anolis aequatorialis Werner, 1894 and Hylodes appendiculatus Werner, 1894. Both species were described based on single specimens, with no more specific type localities than “Ecuador” (Werner 1894a,b). After its description, A. aequatorialis remained unreported until Peters (1967) and Fitch et al. (1976) published information on its distribution and natural history. Anolis aequatorialis is currently known to inhabit low montane and cloud forest on the western slopes of the Andes from extreme southern Colombia to central Ecuador, between 1300 and 2300 m elevation (Ayala-Varela & Velasco 2010; Ayala-Varela et al. 2014; Lynch et al. 2014; D.F. Cisneros-Heredia pers. obs.). Likewise, Hylodes appendiculatus (now Pristimantis appendiculatus) remained only known from its type description until Lynch (1971) and Miyata (1980) provided certain localities and information on its natural history. Pristimantis appendiculatus is currently known to occur in low montane, cloud, and high montane forests on the western slopes of the Andes from extreme southern Colombia to northern Ecuador between 1460 and 2800 m elevation (Lynch 1971; Miyata 1980; Lynch & Burrowes 1990; Lynch & Duellman 1997; Frost 2016). To this date, the type localities of both species remain obscure. The purpose of this paper is to restrict the type localities of Hylodes appendiculatus Werner, 1894 and Anolis aequatorialis Werner, 1894 based on analyses of the travel journals of their original collector.

Male (left) and female (right) brown anoles (sizes are not to scale)

Among their many contributions to evolutionary biology, anoles have historically been at the forefront of research on sexual dimorphism. Much of the recent work in this area focuses on a very general question – how do males and females express different phenotypes despite sharing essentially the same underlying genome?

Not surprisingly, the answer often depends on the type of scientist you ask. An endocrinologist might say that the development of sexual dimorphism requires hormones such as testosterone and estradiol. A quantitative geneticist might reply that it involves the reduction of genetic correlations between the sexes. A molecular geneticist might view the problem as one of regulating the expression of shared genes differently in each sex. Can anoles help us put these different perspectives together into a unified framework for sexual dimorphism?

To address this question, our lab at the University of Virginia teamed up with Christian Cox (Georgia Southern), Joel McGlothlin (Virginia Tech), and Daren Card, Audra Andrew, and Todd Castoe (University of Texas, Arlington). The full details are available in The American Naturalist, but here’s a quick rundown of the highlights:

We conducted a breeding study on a captive colony of Anolis sagrei, a species in which adult males average nearly three times the mass of females. We found that the extent to which males and females share heritable variation for body size starts out high early in life, but declines rapidly as sexual dimorphism emerges during development.

This breakdown of genetic constraint is mirrored by a sharp increase in the sex-biased expression of hundreds of autosomal genes in the liver, particularly those genes that regulate growth, metabolism, and cell proliferation. In other words, although male and female anoles share most of the same genes, each sex tweaks the expression of these genes in different ways as development progresses.

How do they do it? We also show that some of the patterns of male-specific gene expression that emerge later in life can be induced by treating juvenile females with testosterone. Putting these pieces together, we propose that hormones help male and female anoles regulate their shared genes in different ways, which allows them to attain dramatically different body sizes and also helps break down genetic correlations that would otherwise constrain their independent evolution. We hope that our study encourages other Anolis biologists to continue building connections between evolutionary genetics, developmental biology, and endocrinology!

One of the long-faced members of the carolinensis clade, Anolis brunneus.

Several years ago, I wrote a series of papers and blog posts about the diversity of anole head shape and its developmental origins. My colleagues and I touched on disparate topics such as whether the head differences among species are similar to post cranial ecomorphology, whether the patterns of cranial modularity are conserved across anoles, and the developmental bases of sexual dimorphism in skull shape.

Since starting my own lab at Loyola University in Chicago last year, I am revisiting these projects on skull evolution. Like in much of science, I have found that my early forays into this area created more questions than answers. Understanding the diversity of skull shape among anoles and other iguanid lizards will be one of the first focal areas of my new lab. We are currently mining museum collections to understand how the variation in anole skulls compares to iguanid lizards more broadly. The ultimate goal, however, is to return to questions about the developmental origins of this variation. Just how many different ways has development been modified to generate all the variation we observe in adult anatomy? We do not yet know.

This is where my attention turns to you. To thoroughly flesh out the developmental origins of anatomical diversity, I must have robust sampling of species across the iguanid phylogeny. I am asking the community to please think of me and my students if you have extra breeding animals, eggs, or hatchlings of any species of anole or another iguanid lizard. I am happy to help offset the cost of the animals or collaborate in a mutually beneficial manner.

One of the most exciting species that have recently had the fortune to work with is Anolis hendersoni. For its body size, this species has one of the longest faces of all anoles. In this case I was contacted by the owner of Backwater Reptiles who had several A. hendersoni adults that we are hoping to get eggs from over the next year at Loyola. The folks at Backwater have been great to discuss “exotic” anoles with as they occasionally receive species like A. woodi, A. cybotes, and Chamaeleolis, all of which could be great additions to my project. This is just one example of how I am trying to broaden the sampling for this project. I ask you, the broader anole community, to help me increase my sampling further. I sincerely thank anyone that has leads for me in advance.

I got up early this morning to put a video camera on one of our A. sagrei eggs that was looking particularly ripe. About two hours later, this little hatchling crawled out. The whole hatching process took about 25 minutes, and I’ve sped up the video by 30x. The video is much more compelling with sound. I personally like “Also Sprach Zarathustra,”  though “Ranz des Vaches” by Rossini had some enthusiastic support in lab. If you have other music suggestions, add them to the comments!

Happy birthday, little one!