Anole Annals

On the 19th of July, 2002, I collected a brown anole (Anolis sagrei) male from the edge of a rice paddy next to a tarred road in Santzepu, Sheishan District, Chiayi County, Taiwan, as part of a diet and reproductive cycle study. As I removed it from the fine-meshed fishing scoop net, which I used for capturing it, I found that it had two tails. I later found that even though the lizard had no abdominal fat bodies the animal was still in a reproductive state, indicating that it was not only able to regenerate a tail twice, but it could also still meet the energetic demands for reproduction.

This finding prompted our study to attempt to address the question of whether there are differences in the abdominal fat body weights and liver weights of A. sagrei specimens that had suffered tail autonomy and conspecifics that had not.

We were surprised when we found no statistically significant variations in the monthly mean abdominal fat-body weight indices or monthly mean liver weight indexes of lizards that had not experienced caudal autotomy and those that had. We hypothesize that A. sagrei specimens that experienced tail autotomy most likely met the energetic demands for regenerating the lost portion of their tail by foraging more.

Editor’s Note: for more on two-tailed anoles, such as the photo below, type “tail” or “tailed” into the search bar on the right.

 

Following up with summaries of anole talks at ESA 2016, Dave Spiller presented a broad summary of his and his colleague’s (Tom Schoener and Jonah Piovia-Scott) research investigating the effects of hurricanes on long term food web dynamics of small Bahamian islands, which has just recently been published in Ecology (see Spiller et al. 2016).

Spiller opened by explaining some of the patterns of food web dynamics that have been learned from this research. Most notably, that the elimination of brown anoles – which act as top predators in these simple ecosystems – leads to increased levels of herbivory as arthropods experience a relaxation of predation pressure (Spiller and Schoener 1990).Specifically, the presence of a common moth (Achyra rantalis) on islands without brown anoles can lead to extreme levels of herbivory upon a common island plant, Sesuvium portulacastrum (below).

Spiller and his colleagues began to notice that following hurricanes, one of the most extreme natural disturbance events in this region, islands with lizards experienced a much more rapid recovery of Sesuvium .

In an attempt to understand how ecosystems may be stable despite experiencing extreme disturbance regimes, Spiller and colleagues measured the percent ground cover of Sesuvium and abundance of Achyra moths on 11 islands with lizards present and 21 islands without lizards annually for 10 years.

Overall abundance of Achyra was 4.6 times higher on no-lizard islands than on lizard islands. The percent cover of Sesuvium exhibited lower temporal variability on lizard islands when the study site was undisturbed by hurricanes, and higher recovery rate on lizard islands following hurricanes.

Spiller concluded by suggesting that these stabilizing phenomena are linked to a trophic cascade in which predators (brown anoles) control herbivores (Achyra moths), and therefore enhance plant recovery following hurricanes.

It’s amazing the size of prey that some anoles will try to get down their throats (and who could blame them?).  Here’s an example from Daffodil’s Photo Blog. And here’s another example from the same source.

 

AA stalwart Tony Gamble has provided these two photos from exhibits at the Milwaukee Public Museum. The one above is a knight anole, whereas below, an Archaeopteryx appears to be dining on a green anole, significantly increasing our understanding of the age of the anole radiation.

AA’s other Wisconsin stalward, Greg Mayer, provides the low-down: “The equestris  is from the Rain Forest exhibit. This is a fabulous exhibit based mostly on the Costa Rican rain forest, but including some other tropical/rain forest elements. I take my vert. zool. class there every year, and have used it as part of the pre-trip preparation for Costa Rican field classes. It was funded in part by the NSF, and involved lots of field work–they did latex casts of trees to get the bark right for life size models of them! The Milwaukee Public Museum was much involved in making Costa Rica the center of tropical studies for US-based scientists. The MPM was slightly independent of OTS. They had their own field station, La Tirimbina, which is very nice–I’ve taken students there 2 or 3 times.

Allen Young, the MPM lepidopterist, was the driving force for Milwaukee’s tropical studies. He wrote about his work at Tirimbina in Sarapiqui Chronicle (Smithsonian Institution Press, Wash. DC, 1991). Young first went to Costa Rica in 1968 with OTS, then focused his work at Tirimbina. (Bob Hunter, who owned Tirimbina at the time, also owned part of La Selva, and was involved in getting both places established as field stations.) MPM’s stake in Tirimbina was sold off by then Milwaukee county executive (now governor) Scott Walker, who couldn’t imagine why a natural history museum in Wisconsin could be interested in Costa Rica. Fortunately, another conservation organization bought MPM’s share.

Others were involved in the exhibit creation as well, and though I’ve never asked him, I’ve always thought the Anolis equestris behavior display in the rain forest exhibit may have been a contribution of Bob Henderson. There are several males and females (not sure if they’re freeze-dried, or some kind of model), showing various levels of agonistic display– fans, nuchal crests, open mouth, raised posture– set out on vines/branches. A question I ask vert. zool. students about this display case is how could they tell the lizards are arboreal, even if they were not posed on branches.”

And with regard to the photo below: “The other picture is from the Third Planet exhibit (I’m always tempted to write Third Rock!), from a section of that very good exhibit on the Hell Creek Formation and the end Cretaceous vertebrate extinctions. The MPM has two Archaeopteryx models made up with feathers, and the one in the pic has a dried or model Anolis carolinensis in its mouth, painted a fairly bright green. The other Archaeopteryx model is better done, and that one goes out on loan periodically to other museums (I think I’ve seen it at the Field Museum).

A recent paper in the Caribbean Journal of Science on the diet of the Lesser Antillean barn owl on Dominica revealed that anoles, specifically the native species A. oculatus, are a very frequent prey item, constituting 193 of the 517 prey items. The authors note that owls are nocturnal and anoles are diurnal and proffer three explanations: 1. the predation occurs at dawn and dusk, when both species are normally active; 2. the anoles are active around lights at night; 3. the owls are catching the anoles while they sleep. We’ve discussed this topic before: owls are known to eat anoles in Cuba and many other places in the neotropics, and there’s the great photo re-posted below (original post here). As far as I’m aware, that’s the only direct observation of an anole being preyed upon by an owl (although a quick search on Google Images will yield many photos like the one at right). We’ve also discussed the parallel  issue of bat predation on anoles in these pages. Clearly, more data are needed!

I was recently doing some anole field work in the Gulfo Dulce area of Costa Rica, and I came across a lizard that has me stumped. Perhaps some more experienced AA readers have some insight – any idea what species this little guy is? To me, it looks a bit like A. limifrons and a bit like A. carpenteri, but not completely like either (and carpenteri isn’t supposed to occur in the Gulfo Dulce area). It was in an area of pretty thick primary forest, perched about 6 ft or so up a tree trunk, and it ran quite high when I pursued it. I’d appreciate any tips!

Although camera traps have historically been used to study endotherms, particularly mammals, recent studies have found them to also be effective for reptile research, given proper conditions. Indeed, Welbourne and colleagues (2015) found them to be as effective as complementary methods for detecting reptiles.

We conducted a study in the Lower Urubamba Region of the Peruvian Amazon using camera traps to monitor mammal use of natural canopy bridges for crossing over a pipeline road between September 2012 and October 2013 (see Gregory et al. 2014 for further description). Unexpectedly, we ended up with numerous records of reptiles, including many of Uracentron flaviceps, which is easy to identify because if its large body size, and records of 17 individuals we have not been able to identify. We suspect many of them to be Anolis species, but they are very difficult to see. We would be grateful for identification assistance from the Anolis researcher community.  Below we show pairs of images for each individual: the full camera trap photo and then a cropped image of just the individual. Please e-mail me (GregoryT@si.edu) with the individual number (listed above each photo pair) and any thoughts you have about identifications. Thank you Anolis research community!

Gregory, T., Carrasco-Rueda, F., Deichmann, J.L., Kolowski, J., and Alonso, A. (2014). Arboreal camera trapping: taking a proven method to new heights. Methods in Ecology and Evolution 5:443-451.

Welbourne, D.J., MacGregor, C., Paull, D., and Lindenmayer, D.B. (2015). The effectiveness and cost of camera traps for surveying small reptiles and critical weight range mammals: A comparison with labour-intensive complementary methods. 42:414-425.

Unknown sp. 17

Unknown sp. 16

Unknown sp. 15

Unknown sp. 14

Unknown sp. 13

Unknown sp. 12

Unknown sp. 11

Anolis cf. punctatus (#10)

Unknown sp. 9

Unknown sp. 8

Unknown sp. 7

Unknown sp. 6

Unknown sp. 5

Anolis sp. 4

Anolis sp. 3

Anolis sp. 2

Anolis sp. 1

 

 

As anole enthusiasts, most of you have probably seen anoles engage in lock-jawed fights, where two rival males grab onto each other’s jaws and try to throw their opponent off a contested perch. These encounters are extremely physical, often leaving one or both contestants injured. While these fights are exciting to watch, they are relatively rare in nature. Most contests between anoles are resolved without fighting using stereotypical display behaviors, where the two lizards head bob and dewlap at each other until one anole submits. In these cases, dominance is conveyed not through physical defeat, but from the animals’ perceptions of their opponents.

This of course begs the question, what criteria do anoles use to evaluate their rivals? How do they decide if they should keep pushing or if they should back down during a fight? A lot of research has attempted to answer this question. Many of these studies are performed in the lab using staged contests between two individuals, called arena trials. These studies generally look for differences between the “winners” and the “losers” of each trial to identify potential dominance signals.

When I was an undergraduate in Dr. Michele Johnson’s lab at Trinity University, we ran a lot of arena trials to understand how lizards interact. At the same time, I was part of a collaborative biomath team that included McKenzie Quinn (another undergrad) and me, and our advisors Michele and mathematician Dr. Cabral Balreira. We had been working together to develop a mathematical model of lizard energy use, and as that project was wrapping up, we were considering other directions our team might pursue. We came up with the exciting idea that we might be able to use those arena trials we’d been doing in combination with Cabral’s area of expertise –the development of ranking algorithms, usually applied in sports. In Cabral’s work with sports ranking algorithms, he summarizes the win-loss results of a sports tournament to identify the overall best and worst teams. These rankings allow you to incorporate how each team performed against teams of varying skill levels, providing a more holistic metric of their abilities than individual game results would. This led us to a “light bulb” moment. By applying a sports tournament framework to a lizard population, we could see how individuals compete against different opponents to determine what traits are associated with social dominance. This also allows us to evaluate lizard dominance using quantifiable metrics instead of qualitative metrics.

We first created a tournament in which each lizard in our population (n=18) competed in six arena trials. We then used sports ranking algorithms to generate a dominance hierarchy for the population and used stepwise linear regressions to compare rank (y variable) to morphological and behavioral traits (x variables) of each lizard. We found that rank was highly predicted by aggressive behavior, indicating that lizards that displayed more during the tournament tended to be more dominant (surprisingly, body size didn’t predict dominance in our trials!). We then applied this same logic to a natural system (studying the green anoles in Palmetto State Park in Gonzales, Texas) to see if “dominant” anoles in the wild had the same characteristics as “dominant” anoles in the lab. In the wild, male anoles fight over territories, because controlling a territory gives owners uncontested access to the food and potential mates within it. Therefore we can “rank” males based on the size (bigger = better) and quality (more females = better) of their territories. When we compared territory size and quality (y variables) to morphological and behavioral traits (x variables) as before, we found that traits related to fighting ability, such as head width (a proxy for bite strength), were the best predictors of dominance in the natural system (but again, body size was not predictive of territorial success).

Together, our results indicate that dominance cues in anole contests are often context specific. In brief arena trials between unknown males, signals that reveal immediate intentions (i.e., display behaviors) are especially important. In contrast, males in the wild have to back up their bluster, and thus actual fighting ability is more highly favored in the long run. If you are interested in this study, we hope that you check out our recent paper to view the details of our results and methods.