The influence of light on visual discrimination of sexually dichromatic dewlap color in male and female brown anoles

Signal theory hypothesizes that the ability to discriminate variation in visual signal color should vary by light environment so that visual signals evolve conspicuousness sufficient to allow for discrimination in some light environments but not in others. I quantified the spectral variation of male and female dewlaps from a central Florida population of Brown Anoles, Anolis sagrei. I applied these spectral data to a visual model that integrated information about A. sagrei visual physiology to estimate the discriminability of male and female dewlap color in different levels of sun exposures that characterize light variation in two adjacent habitats (open versus forest shaded environments). Dewlap spectral variation was sexually dichromatic in all light environments. However, the likelihood that dewlap color would be discriminable varied with sex, habitat and levels of sun exposure. I found many correlations between aspects of dewlap spectral variation and color discriminability. I placed the correlations of dewlap spectral variation and color discriminability in a backwards step-wise multiple regression and found three spectral reflectance strategies in which male and female dewlaps maximized color discriminability in the available light. In both habitats and under the majority of sun exposure by habitat combinations during mid-day sun, a reduction of brightness overall but an increase in short wavelength (ultraviolet (UV)) chroma for females and long wavelength (yellow-red) chroma for males increased dewlap color discriminability (reflectance strategy 1). Reflectance strategy 2 was specific to full mid-day sun on the forest floor, and dewlap color discriminability was related to an increase in brightness and an increase in short wavelength chroma (UV) for females and short and medium wavelength (UV, blue and green) chroma for males. Reflectance strategy 3 occurred when dewlaps are viewed in full sun on the forest floor at dawn or dusk, and dewlap color discriminability was maximized by a reduction in red brightness in females and a reduction in red brightness but increase in short and medium wavelength (UV, blue and green) chroma of males. These findings are discussed briefly with respect to what is known about how pigments generate color in the dewlaps of Brown Anoles.