Date of Award

6-2013

Document Type

Open Access

Degree Name

Bachelor of Science

Department

Biology

First Advisor

Leo J. Fleishman

Language

English

Keywords

lizard, dewlap, colors, brightness

Abstract

Lizards of the genus Anolis communicate almost exclusively with visual signals that include the extension of a colorful, extensible throat fan called a dewlap. Dewlap color exhibits impressive diversity across anoline species and is thought to have evolved due to two simultaneous sets of selection pressures: (1) selection for high detectability, and (2) selection for a color that is different from the dewlap color of other sympatric species of Anolis in order to facilitate species recognition. In order for a dewlap display to be successful, it must be “detected” by the intended viewer. We hypothesize that a detectable dewlap should be distinct from its natural background in terms of brightness and color. We collected and analyzed spectral data for dewlap color and habitat light conditions for four species of anoles inhabiting the island of Puerto Rico. Background and dewlap colors were plotted in a three-dimensional tetrahedral perceptual color space based on the relative stimulation of each of the four types of cone photoreceptors of the anoline visual system. We found that for each species, dewlap colors were distinct from the range of background colors. We also found that for three out of the four species, dewlaps were typically brighter than the background patches of their habitats. We carried out an additional behavioral experiment testing the likeliness of an anoline visual response being elicited as a function of the difference in brightness between a stimulus and a complex background. Our data suggest that the more a dewlap differs in brightness from the brightness patches in its background, the greater its visibility. Results from both experiments support the hypothesis that natural selection for high detectability in a complex environment has played a major role in the evolution of anoline lizard visual signal color.

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