Photosensitivity in the skin of the lizard, Anolis carolinensis

Rapid body color brightening is associated with exposure to a stressor in an Anolis lizard

Many species use color change to optimize body coloration to changing environmental conditions, and drivers of rapid color change in natural populations are numerous and poorly understood. We examined factors influencing body coloration in the Water Anole (Anolis aquaticus Taylor, 1956), a lizard possessing color-changing stripes along the length of its body. We quantified the color of three body regions (the eye stripe, lateral stripe, and dorsum) before and after exposure to a mild stressor (handling and restraint). Based on current understanding of the genus Anolis Daudin, 1802, we hypothesized that exposure to a stressor would generate genus-typical skin darkening (i.e., increased melanism). Contrary to expectations, stress consistently brightened body coloration: eye and lateral stripes transitioned from brown to pale blue and green and the dorsum became lighter brown. Sex, size, and body temperature did not correlate with any aspect of body coloration, and a laboratory experiment confirmed that light exposure did not drive brightening. We propose that color change may serve to reduce conspicuousness through disruptive camouflage; lizards tended to display brighter stripes on mottled green–brown substrates. Together, these results improve our understanding of Anolis color change diversity and emphasize the need for a broader interpretation of the mechanism and functions of color change across taxa.

Behavioral changes in Anolis carolinensis following injection with fluoxetine

Eight adult male lizards of the genus and species Anolis carolinensis were used in this experiment. In order to induce aggressive responding, animals were caged separately and daily underwent pairing with another male, during which aggressive responses and changes in skin color were measured. After obtaining a baseline measure of aggressive responding, animals were injected either with fluoxetine or vehicle-controls in a cross-over design. Subjects were then exposed to five more days of (non drug) pairing with the intruder male, after which they underwent a second trial with fluoxetine/vehicle. Finally, two post-drug paired-trials were obtained. Fluoxetine injection significantly reduced the aggressive responding in the males while causing the postorbital eyespot to significantly darken. Subjects also showed increased aggressivity and skin-color reactivity subsequent to the two drug trials, although it is unclear if the fluoxetine, or non-specific factors of the injection paradigm, accounted for these changes. These results suggest that serotonergic CNS systems tonically regulate aggression in Anolis carolinesis, similar to that seen in many other species. They further suggest that eyespot-darkening and aggressive responding can be pharmacologically dissociated, implicating serotonin in the regulation of this phenomenon.