Environmental determinants and controls of skin color change in neotropical anurans

Physiological color change is a strategy present in many groups of vertebrates and invertebrates. Animals showing this behavior have become model taxa in the study of camouflage because they are able to respond dynamically to changes in the environment. A number of studies have looked at the ability of amphibians to change skin coloration, in a phenomena known as physiological color change. In the physiological response, dermal pigment-containing cells rapidly react by modifying the distribution of pigments. Environmental factors such as light intensity and background color have been known to be very important cues on amphibian physiological color change, but the ecological function of these changes, in the context of a changing environment, is still unclear. Additionally, due to the presence of visual pigments in chromatophores, amphibians can aggregate or disperse pigments in specific areas of the skin, as a direct response to changes in the intensity of light; response that raises new questions about the benefits and drawbacks than an (visually) uncontrolled change might have on anuran ecology. However, studies have been limited to early stages. This study investigates how environmental factors affect color change in anurans and to what extent these changes are controlled by the individual. First, I present a review of the importance of coloration for anuran ecology and discuss the current issues dealing with color change experiments (Chapter I). Then, I present the results of the first experiment, in which I tested the ability of the Panamanian frogs Gastrotheca cornuta and Strabomantis bufoniformis to change skin coloration in response to light intensity and background coloration (Chapter II). I show that both species respond to changes in light and background color, but there are interspecific differences, probably due to the species-specific habitat characteristics (i.e. Forest canopy and floor respectively). Then, in a second experiment on Hypsiboas rosenbergi adults, I demonstrate the ability to change skin coloration as a direct, visually uncontrolled and localized response to light. These findings suggest that changes in adult frog skin coloration play an important role in camouflage and thermoregulation, and give a key, yet missing, component in understanding the behavioral and evolutionary implications of color change in animals.