Anole Annals

Imagine running quickly among a network of obstacles while attempting to maximize performance. It’s not an easy task, but one that arboreal lizards perform every day. In addition to variable inclines and perch diameters, arboreal lizards often encounter obstacles in the form of branches. The size of these branches, and their spacing, could have a significant impact on locomotor performance, such as sprint speed. Using a clever experimental design, Zachary Jones and Bruce Jayne (University of Cincinnati) recently determined how these important characteristics impact running performance in Anolis sagrei, A. carolinensis, and A. angusticeps (Click here to read paper from the Journal of Experimental Biology).

(A) Dorsal view silhouettes of the three Anolis study species compared against the diameter of the running surfaces. The lizards and cross-sectional areas of the running surfaces are all shown to the same scale. All running surfaces were cylindrical, but only one-half of the largest diameter is shown. (B) Schematic diagram of the peg treatments (not to same scale as the lizards). Pegs along the top center were placed at 10 cm (TC10) or 20 cm (TC20), horizontal pairs of pegs (HP) were placed every 10 cm, and alternating pairs of pegs (AP) oriented vertically or horizontally were placed every 10 cm along the length of the primary running surface (gray). The cylinder with no pegs (NP) is not shown.

Similar to previous studies, increases in perch diameter resulted in increased sprinting speed. With pegs added to the perch, things changed. When pegs were placed at 10cm intervals, and sticking directly up from the top of a 3cm-diameter perch, running performance of A. sagrei was sliced in half compared to running on a peg-free perch or a perch with pegs sticking out from the sides. Especially for the smaller perch diameter treatments, the number of pauses increased with increased branching, and this was greatest when the pegs came out from the top of the perch. This increase in pausing results in a decrease in overall speed (increased transit time) as they move through their habitat.  This is also a result found by Higham et al. (2001), where turning angles in the locomotor path resulted in increased pausing in Anolis lizards.  The take home message is that branching can have a negative impact on locomotion, forcing lizards to take longer getting from point A to point B.  This could make them vulnerable to predation or reduce their ability to effectively capture prey.
Luckily, the array of pathways in an arboreal habitat provides an opportunity for Anolis lizards to select what works best for them.

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Another week brings another nice batch of anole publications from a few previously held meetings. This batch comes from a combined special issue of General and Comparative Endocrinology that features articles from The Inaugural Meeting of the North American Society for Comparative Endocrinology (NASCE) and the 7th International Symposium on Amphibian and Reptilian Endocrinology and Neurobiology (ISAREN) held last July.  The papers from this meeting are now available at the journal’s page at Elsevier ScienceDirect.

Wade (2012) provides a nice review of structure and function of three sexually dimorphic anole features in green anoles (Anolis carolinensis): the forebrain, the dewlap neuromuscular system, and the copulatory neuromuscular system.  She also reviews comparative studies across anole species of the dewlap system and provides a detailed discussion of endocrine regulation in green anoles.  Cohen & Wade (2012) investigated “Aromatase and 5 alpha-reductase type 2 mRNA in the green anole forebrain: An investigation of the effects of sex, season and testosterone manipulation.”  Finally, in a non-anole paper about other iguanid lizards Hews et al. (2012) investigate “neuroendocrine correlates of aggression differences in adults of two Sceloporus lizard species.”

Male Anolis proboscis. Photo by Jonathan Losos

Of all the anoles great and small, near and far, green and brown, one stands out for its combination of elegance, charm, and mystique. I refer, of course, to the Ecuadorian horned anole, Anolis proboscis, denizen of Andean forests, possessor of an enchanted sword, and all-around lizard of mystery. Now, however, the veil has been lifted, as the first reports on the biology of the previously unknown lizard have just been published in Breviora, a journal of the Museum of Comparative Zoology at Harvard.

Rediscovered by birdwatchers. How embarrassing. Photo by Wanda Parrott.

The mystery comes in three acts. The first concerned the continued existence of the horned anole. The species was discovered in 1953 and over the next 13 years, another five were found, all male like the first, all from the vicinity of the Ecuadorian town of Mindo. Then, for four decades…nothing. Many feared the species extinct, perhaps a victim of the deforestation that has ravaged so much of the Western side of the Andes. All this changed in 2005 when a group of birdwatchers spied one crossing a road near Mindo (mind you, this is an arboreal lizard—insert your own joke). Anolis proboscis lives!

The photo above made its way onto the internet and to the attention of Steve Poe, an expert on locating hard-to-find anoles, who led a team of American and Ecuadorian scientists back to Mindo in the summer of 2009. Poe’s approach to finding day-active anoles is seemingly perverse: he stays up all night looking for them. The reason is simple: many anole species sleep on narrow twigs or leaves, presumably because approaching predators will produce vibrations on the flimsy perches, alerting the lizards to impending danger. Although this strategy may be effective in avoiding predators that creep, crawl or slither along branches, it’s not so well-suited to avoid detection by flashlight-toting herpetologists, who are attuned to locating the tiny reptiles—which conveniently blanch to a pale color at night—even when they’re roosting 20-30 feet high in the canopy. Poe’s team quickly located a large number of lizards, establishing that the species not only exists, but seems to have a healthy population.

Unbeknownst to Poe, another team of researchers independently had discovered a new horned anole locality. This team, from the Ecuadorian Museum of Science in Quito, located five specimens of the horned anole at two sites 11-13 km northeast of the original collecting locality, slightly extending the known range of the species. Both groups published detailed descriptions of the anatomy of the species—the Ecuadorian group last year and Poe’s team as the first of the Breviora set published today—describing previously unknown variation in horn size and shape, as well as differences in color and patterning both among males and between the sexes.

And, speaking of differences between the sexes, that leads to the resolution of mystery number two. Ever since the species was first described and the initial half dozen specimens collected, lizard enthusiasts have wondered—what about the females? Do they have horns, too? Of course, in the absence of any information on the natural history of the species, it was hard to have an informed opinion. Is the horn used in self defense, in which case the lady lizards could probably use one as well as the guys? Or is it used by males to fight amongst themselves, or even as an ornament used to woo or titillate? Nobody knew, and so it was anybody’s guess whether the females were nasally adorned or not. But now we know the answer. Before I reveal it, take a moment and take a guess: yes or no? When you’re ready, scroll past the lovely photo of another male and see for yourself.

Male Anolis proboscis. Photo by Luke Mahler

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Fig. 1 from Harrison and Poe illustrating dewlap differences between males (top) and females (bottom).

The function and evolution of anole dewlaps have been the focus of studies for decades. As flashy, showy displays of color, it’s no wonder that dewlaps even captured the attention of Darwin. However, most studies to date have focused solely on male dewlaps leaving female dewlaps much neglected (but see Johnson & Wade, 2010 and Vanhooydonck et al., 2009). While the possession of dewlaps is less common in females than males, and female dewlaps are often rather diminutive compared to the male’s, the mere presence of female dewlaps in a good number of species, combined with striking variation in color, pattern and size across the genus, begs the question of what is driving the evolution and maintenance of such female ornamentation?

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As reported previously at Anole Annals, The 2012 meeting of the Society of Integrative and Comparative Biologists (SICB) was packed with anoles (1, 2, 3, 4, 5, 6).  At least 17 talks or posters mention Anolis in title (complete list below the fold)!  The abstracts from this meeting are now available via PDF from the Society’s journal Integrative and Comparative Biology.  I was excited to see all of the new anole content as it appeared on Web of Science and other indexes, but disappointed that these titles were only associated with abstracts.  To all of you who presented: please get this stuff published, many of your titles are very compelling and the anole community can’t wait to learn more!

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