Carotenoid-Based Dewlap Color as a Visual Signal in Social Communication of Brown Anoles (Norops sagrei)

Abstract

Carotenoids have been shown to be important integumentary coloring agents in many birds and fishes. The role of carotenoids as a prominent integumentary coloring agent of the dewlap has been noted in many Anoline lizards, but the role of carotenoids as a social signal has not been considered. Here, I investigated some proximate causes of male and female dewlap color, and found that males and females differed in pterin pigment concentrations but not in carotenoid concentrations. I also found that sexes differed in UV as well as long wavelength reflectance, and that carotenoid-based UV color correlated positively with body condition. I then used a visually-based color detection model that incorporates knowledge about UV vision to simulate and describe the conspicuousness of dewlap colors as conspecific lizards should see it, under different forest light environments. Two sets of behavior experiments were performed to test assumptions about signal spectral variability, signal honesty and signal use. One set of experiments investigated a potential role for UV (a carotenoid-based dewlap color) to be used as a visual signal in contests for females. I quantified natural dewlap coloration, and paired males into size-matched dyads that naturally differed in UV reflectance. Males that won male-male contests, and copulated with females, had lower UV reflectance than males that lost contests. I then manipulated the UV component in dewlap colors, and I investigated whether the manipulation changed the contest outcome. While manipulations had no effect on contest outcomes, the underlying natural colors still correlated with contest success. A final set of experiments investigated the dual contributions of nutritional stress and carotenoid access on male dewlap color. I found that carotenoid availability altered UV and long wavelength reflectance, and that UV amplitude decreased with nutritional stress. These results summarily suggest that dewlap color is a signal used to communicate information about the senders’ phenotypic quality to the receiver, and that dewlap color (including ultraviolet wavelengths) is highly visible in some light environments. Furthermore ultraviolet aspects of dewlap color among males correlates with contest success. Finally, dewlap color is at least partially influenced by availability of carotenoids during adulthood, and can convey information about an individuals’ health.