Animal signal colors evolve to efficiently stimulate conspecific visual systems. The sensory drive hypothesis proposes that species differences in habitat light conditions favor the evolution of color diversity. The strongest support comes from aquatic systems, while terrestrial systems offer fewer convincing examples. Anolis lizards occupy diverse habitats and signal with a colorful dewlap. Dewlap visibility depends on perceived chromatic contrast with the background. Visual-system modeling has shown that red dewlaps are most visible in most habitat types. However, a majority of species possess white or yellow dewlaps. In a recent behavioral study we showed that low light conditions can sometimes make yellow and white colors more visible, by altering chromatic contrast perception with the background. Using 17 Caribbean Anolis species we showed that cut-on wavelength, a measure of dewlap color in a white-to-red continuum, correlates with habitat light intensity. Pairwise comparisons revealed that red dewlaps are most visible in bright habitats, whereas yellow and white are more visible in darker habitats. We conclude that sensory drive has contributed to the evolution of dewlap color differences through the interactive effects of total habitat light intensity and chromatic contrast perception and may provide a mechanism for speciation among anoles.

Field data collection and computer modeling.