Frogs Are Lovers; Anoles Are Fighters – Updates From SICB

Sometimes anoles are lovers, too. But even when they love, they seem to fight. Photo of Anolis carolinensis taken from Wikipedia.

Greetings again from San Francisco! The anticipation for  yesterday’s Animal Communication session was palpable. Usually a big Anolis hit at SICB, the Communication session did not fail to impress. The session was divided into two sections – Lovers and Fighters. Can you guess which one had all the anole talks? Three out of the five talks in the Fighters session were about anoles. Incidentally, most of the talks in the Lovers session were about tree frogs. This was perfectly to my liking – I’ll take the blood, guts, and gore any day. The three Anolis talks presented fascinating new work.

The first was by Jessica Edwards, a graduate student working with Simon Lailvaux at the University of New Orleans on aggressive encounters between Anolis carolinensis and A. sagrei, which has successfully invaded much of A. carolinensis‘ range. In a previous study, Jessica and Simon found that A. carolinensis tends to perch higher in the presence of A. sagrei than when found alone.  For her experiment, Jessica placed one male of each species into a large cage with a single perch. At the top of this perch she placed a heat lamp, so that there was one optimal site (warm top) and one sub-optimal site (cool bottom) on the perch. She then scored behaviors and recorded the victor in each trial.  She found that relative dewlap size was a good predictor of trial outcome, and that the each species was about equally successful at obtaining the optimal perch, although A. sagrei did have a slight advantage. She repeated this experiment using females of each species, and found something exciting and perhaps unexpected – Anolis sagrei was the clear victor in all but one of several dozen trials! Jessica posits that, in the wild, female A. sagrei push female A. carolinensis higher up in the trees. In polygynous systems such as anoles, where one male defends a group of two or more females, then we would expect the males to go where the females do, and so would expect males to increase their perch heights, as well.

The next anole talk was given by Ellee Cook, an undergraduate biology student working with Dr. Michele Johnson at Trinity University. Ellee’s research focuses on how parasite load influences social signals in Dominican Anolis lizards. In a previous study, Ellee had found that parasitized A. brevirostris had duller dewlaps, and that dully colored lizards displayed less frequently than males with fewer parasites. This summer, Ellee followed up on this study by examining A. distichus, the sister species to A. brevirostris, and A. cybotes, the widespread trunk-ground anole. She also extended this study to different elevations because previous studies have shown that parasite load increases at higher altitudes.

She found that larger A. cybotes males had brighter dewlaps, meaning there was more white in them, and lower yellow saturation, which refers to the richness of the color. In some, but not all, populations of A. cybotes, she found a negative relationship between dewlap brightness (i.e., amount of white) and parasite load.

In eastern populations of A. distichus, she found a positive relationship between parasite load and dewlap brightness, while those with greater body condition (mass per snout-vent-length) had duller (less white) dewlaps, with more red and yellow. These results parallel what she found in A. brevirostris, as individuals with better body condition also had fewer parasites and more vibrant dewlaps. For those that are interested, Ellee described hue as the dominant wavelength of a color (essentially the color of the rainbow), saturation as the rightness or intensity of a color, and brightness or luminance as the amount of white in a color.

Justin Henningsen, from the University of Massachusetts, Amherst, gave the final anole talk of the Fighters session. Previous studies have shown that dewlap size is an honest indicator of male quality – in some species of anoles bigger dewlapped males have stronger bites. Justin’s work focuses on figuring out why there aren’t cheaters. Unless there are costs associated with the conspicuous signal, such as increased predation risk, then weaker males could evolve bigger dewlaps. Justin used recapture studies and clay models to determine whether or not predation risk is a cost associated with the dewlap, a conspicuous ornament in anoles. To this end, Justin performed a recapture study in a population of A. carolinensis that were divided into two groups. Individuals from one group had their dewlaps surgically disabled such that they could engage in every normal behavior except extending the dewlap. Members of the other group underwent a sham operation, meaning that they were surgically opened in the appropriate anatomical area, but did not have their dewlaps disabled.

He found similar rates of lizard recapture (quite low) for lizards from both treatments. This could suggest that there is no difference in predation risk between ornamented and altered males. To my eye, it could also mean that the risks of an ornament (predation) are counterbalanced by its benefits (territory). Aggressive behaviors in anoles are hierarchically structured. Perhaps the removal of a key visual component to display behavior makes altered males subordinate to intact males. It is also possible that they need a bigger sample size. Of 60 lizards deployed per treatment, they only recovered a handful.

Finally, they deployed clay models of anoles to measure predation. There were three groups clay models: green anoles with pink dewlaps, green anoles with green dewlaps, and green anoles with no dewlaps. They found the highest level of predation (measured as bird bites) on models possessing a pink dewlap, suggesting that the ornament may increase predation risk in anoles, even though lizards do not always have them extended.

What did I learn? Anoles have to contend with parasites, predators, and competitors. It’s no small wonder lizards are fighters.

About Martha Muñoz

Martha is a PhD candidate at Harvard University studying the evolutionary ecology and thermal physiology of anoles. She works in Jonathan Losos' lab and focuses on the cybotoid anoles from the Dominican Republic. Website: www.marthamunoz.weebly.com

5 thoughts on “Frogs Are Lovers; Anoles Are Fighters – Updates From SICB

  1. Very cool post, thanks for sharing. I’m curious though, did Justin Henningsen mention if any other work has been done on why dewlap size is an honest signal? Or if the previous studies gave possible explanations?

    1. Hi Dan,
      Thanks! Offhand I do not remember which work he referenced. I’ve emailed him so that he can clarify.
      Cheers,
      Martha

    2. Hi Dan,
      I never heard back from Justin, but check out Vanhooydonck et al. (2005) in Functional Ecology. They found that in A. grahami and A. lineatopus, but not A. valencienni, bigger dewlapped males had stronger bites. They suggest that interspecific differences in territoriality may have something to do with this pattern.

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