The Visual Ecology of Anolis Lizards

Visual ecology explores how animal visual systems are related to light environments and important visual tasks. Anolis is a species-rich genus of small lizards that rely extensively on vision. Different species occupy habitats with different vegetation structure. The spectral properties of the habitats are similar, but total light intensities vary widely. They possess laterally positioned eyes with broad monocular visual fields, and a small region of binocular overlap toward the front. They possess a high-resolution central fovea associated with analysis of important images. There is a second, smaller, temporal fovea located where the visual fields of the two eyes overlap, which is associated with distance perception during prey capture. Color and brightness vision depends on four classes of single cones with different spectral absorbance curves, including one sensitive to the ultraviolet and a set of double cones. Most species studied possess similar sets of cones. Cone responses are modified by oil droplet filters, which are more variable among species and may play some role in adaptations to habitat light. Anoles communicate with a colorful expandable throat fan called the dewlap. Dewlap visibility depends on contrast with the natural background. Red dewlaps are most visible in bright, unshaded habitats. Yellow dewlaps are most visible in darker, shaded habitats. Visual displays include motion patterns of the head, body, and dewlap. The most highly visible movements are rapid up-and-down, start-and-stop patterns. These often occur at the beginning of visual displays and draw the attention of conspecifics to the displaying animal. Most Anolis species share similar visual-system properties. Differences in light environments interact with visual-system responses to influence the physical properties of communication displays and other visually-based behaviors.