All posts by Lindsey Swierk

Request for Anolis aquaticus Photos and Sightings

Photo by Anolis aquaticus from wildherps.com.

Hello anole enthusiasts!

A quick note and a request from your Anolis aquaticus correspondent. Our new paper on stress-related body color brightening in Anolis aquaticus was recently selected as Editor’s Choice in the Canadian Journal of Zoology. In it, we document a genus-atypical direction of color change following exposure to a stressor, possibly related to optimizing camouflage in the water anole’s unusual habitat. Enjoy!

We are embarking on a new research direction with these wonderful watery critters. In our early stages of surveying, I’d like to ask for your help.

We are exploring morphological and behavioral variation across the water anole’s range to explore several hypotheses related to coloration, habitat lighting, temperature, and stress.
For example, dewlap coloration seems to be fairly variable: water anole dewlaps from our sites at Las Cruces Biological Station are red-orange (left), but at Osa the dewlaps are much yellower (e.g., screen shot taken from Brave Wilderness’s video* on the water anole, right).
jennetOsa

In addition, we’re also interested in knowing a little more about water anoles in the riparian zones that are found in otherwise deforested tropical pasture lands. We’ve put together a map of all known collection sites of museum specimens and published studies (sites shown without exact coordinates in the interest of species’ protection; grey sites are approximate).

Anolis aquaticus collection and sightings

You can help by sharing with us your photographs of water anoles (dewlaps are of special interest, but any photographs would be appreciated) and/or locality data** of Anolis aquaticus sightings or collection. Locations of sightings in pasture/agricultural areas are especially needed!

Lindseyns @ gmail.com
Lindsey.swierk @ yale.edu

Thank you for your help!

*A very enthusiastic group called Brave Wilderness posted a video about their search for the “mysterious” water anole. I have mixed feelings about it and its less-than-perfectly-accurate information, but it certainly captures kids’ imaginations!

**To keep this charismatic species safe and help prevent poaching, please send any GPS coordinates to me directly rather than posting them publicly.

Super-Honest Dewlaps and Trait Scaling Relationships in Semi-Aquatic Anoles

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Anolis aquaticus, the semi-aqautic anole. Photo by Lindsey Swierk

From backyard anole enthusiasts to researchers with decades of experience, dewlaps are a favorite topic of discussion here on Anole Annals. We love documenting the diversity of dewlap colors and patterns (1, 2, 3, 4), judging “best/biggest dewlap” contests (1, 2, 3), and noting dewlap oddities across the genus (1, 2, 3, 4). We’re slowly piecing together an answer to the question of what role dewlaps actually serve in signaling and, in particular, what kind of information they might convey. As you might expect, it’s a pretty complex problem, made even more interesting by the fact that dewlap information content probably reflects the unique pressures placed on individual species.

I’ve recently been working on untangling the mystery of dewlaps in a quirky species of anole, Anolis aquaticus. This water-loving anole is found along streams in pockets of southern Costa Rica and northern Panama, and it has the delightful habit of diving into water when startled. Even among the aquatic-specialized anoles, A. aquaticus is different: it tends to live in ultra-close proximity to water, preferring boulders and crevices directly in the “splash zone” instead of streamside vegetation such as other aquatic species like A. oxylophus. There’s also good reason to think that A. aquaticus has a pretty rich social life – male-female, male-male, and female-female pairs can be found within a few centimeters of each other, and often in dense groups on small rocky islands.

In light of their unusual habitat and living arrangements, we decided to explore how dewlaps correlated with multiple morphological parameters in A. aquaticus. In particular, we decided to use this species to explore a long-standing, but recently debated, paradigm that most sexually selected traits (like dewlaps) scale to body size with positive allometry – or, in other words, that they’re disproportionately large in larger individuals. Last year, we captured male and female (who lack the characteristic reddish-orange dewlap) A. aquaticus and measured multiple sexual and non-sexual traits to test this idea. Our results, available in an accepted article in Integrative Zoology, allowed us to contribute our perspective to the greater understanding of the relationship of sexual selection and allometric scaling patterns. Spoiling part of the punchline, our findings do not support the traditional idea that positively allometry is a hallmark of sexual selection.

The dewlap of Anolis aquaticus. Bar represents 1 cm.

The dewlap of Anolis aquaticus. Bar represents 1 cm.

But, equally as notable, our results also suggest some interesting features of this species, including the information content of its dewlap and how allometric patterns interact to produce sexual dimorphism. We found that dewlaps are “super-honest” signals in A. aquaticus; they could serve to amplify size differences between males signaling at a distance because of their positive allometric scaling with body size. Consequently, our study and a recent study by Driessens et al. 2015 (on A. sagrei), oppose previous ideas that dewlaps approach an asymptote of optimum size to balance the pressures of signaling with predation. Our findings are also novel in that they suggest that dewlap color (redness) may serve to convey information about male weaponry: anoles with redder dewlaps were found to have head shapes that correspond to producing greater bite force.

By comparing allometric relationships between males and females, we can also begin to identify how sexual differences in proportionality link to sexual dimorphism and ecology. For instance, male hind limb length in A. aquaticus is on average larger than that of females, but becomes disproportionately smaller as male body size increases. This opens the door to the idea that, because males are larger than females, limb length sexual dimorphism might be the result of an optimal limb-body size relationship regardless of sex; A. aquaticus of either sex with overlong limbs would probably be at a disadvantage if they needed to flee over narrower surfaces such as branches or vines.

Scaling relationships of snout-vent length and a) mass, b) limb length, and c) head length for male (closed dots, solid line) and female (open dots, dashed line) Anolis aquaticus. Axes are log scaled.

Scaling relationships of snout-vent length and a) mass, b) limb length, and c) head length for male (closed dots, solid line) and female (open dots, dashed line) Anolis aquaticus. Axes are log scaled.

Finally, our results hint at the existence of two life-stage male morphs in A. aquaticus, as already identified in other anole species. Body scaling relationships show that small males have disproportionately small dewlaps, small heads, and large limbs, whereas large males have bigger dewlaps, bigger heads, and smaller limbs than should be expected for their body size. Taken together, these results provide a foundation for future research into “heavyweight” and “lightweight” male morphs and associated behaviors. With their small home ranges and apparently high tolerance for same-sex home range overlap, this could be an especially exciting avenue of exploration in A. aquaticus. In any case, it’s certain that there will be much to learn from this watery, elusive, semi-aquatic anole.

You can read more about this project in our accepted manuscript published online in Integrative Zoology. My co-author on this study, Maria Petelo, is an undergraduate at the University of Hawaiʻi who was supported by OTS/NSF’s Native American and Pacific Islander Research Experience, a program designed to increase the representation of underrepresented groups in the natural sciences.