Ellee "hugging the tree" while Michele chased the lizard.  Photo by Thom Sanger.

Dewlap Color May Indicate Parasite Load, or Anole Biologists Should Hug More Trees!

This post was written by Ellee Cook, a current graduate student at Duke, and a former undergraduate in my and Troy Murphy’s labs at Trinity University.

Dewlap displays are arguably the most striking characteristics of Anolis lizards. In many anoles, we observe variation in dewlap color and display among members of the same species, and in some cases, among members of the same population. However, we do not fully understand what influences this variation, or if variation in these traits has implications for anole communication. Recent work by Julienne Ng and colleagues with A. distichus (reviewed in a post by Jonathan Losos) suggests that genetic factors are determinant of dewlap variation. But, it is unclear whether dewlap characteristics or display behavior vary in accordance with lizard condition, or whether these traits are affected by parasites.

In our paper published earlier this year, we investigated the potential for individual variation in dewlap color and display behavior to serve as honest indicators of ectoparasitic mite load in Anolis brevirostris, a trunk anole from southwestern Dominican Republic that’s closely related to A. distichus. Male A. brevirostris exhibit extraordinary variation in dewlap coloration and have dewlaps that range from yellow to red-orange. Lizards in our study population were naturally parasitized by trombiculid mites.

Ornamental coloration and display behaviors are often negatively affected by parasites. This trade-off occurs because the resources required to produce ornaments often also function in important physiological processes, such as the carotenoid pigments responsible for red-orange ornamental coloration in many organisms that may also act in immune function as free-radical scavengers. Parasitized individuals divert resources to battling infestation, rather than to maintaining ornamentation. Thus, ornament quality can serve as an honest indicator of advertiser quality—might dewlap variation indicate anole parasite load?

We observed the display behavior of male A. brevirostris and then attempted to capture observed individuals to quantify ectoparasite load, body condition, and dewlap coloration. However, we quickly learned that these lizards are easy to see, but fast and tricky to catch. Although they can be noosed, they usually run high into the canopy, where they become difficult to see and nigh uncatchable.

After several frustrating failed captures, we implemented a 2-person “hug-the-tree” method (suggested by the illustrious Thom Sanger) to snag the individuals for this study.  When the lizard was just a few feet above the ground, one of us would quickly throw our arms around the tree just above the lizard, effectively “hugging” the tree. Because A. brevirostris tend to run up rather than down onto the ground, hugging the tree contained the lizard in just a few feet of tree trunk, wherein a second person can catch the lizard by hand or noose. Although there were some long games of “chase-the-lizard-around-the-tree,” hugging the tree ultimately proved very effective for catching A. brevirostris and other anoles with similar habits.  We mastered this method and proceeded to perform focal behavioral observations and capture 30 adult male A. brevirostris. We then counted ectoparasitic mites and estimated body condition using SVL and mass. We used an objective spectrometer to quantify dewlap brightness, hue, and saturation.

We found that heavily parasitized males exhibited duller dewlaps, performed fewer dewlap extensions, and had lower body condition than males with fewer parasites. This suggests that trombiculid mites may be negatively affecting the condition of these lizards, and that individual variation in dewlap color and display behavior may indicate parasite load. These results are intriguing, given that they indicate that variation in ornamental color and display may convey information about advertiser condition.

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