Panther Chameleons, Furcifer pardalis, Behaviorally Regulate Optimal Exposure to UV Depending on Dietary Vitamin D3 Status

Reptiles may bask for reasons other than thermoregulation. One alternative is to regulate homeostasis of vitamin D3, a hormone essential to the health of many reptiles. Maintenance of vitamin D3 homeostasis requires either regulation of exposure to ultraviolet radiation (UV) or ingested vitamin D3. However, the prey items of most vertebrates tend to be low in vitamin D3. Thus, basking may be the primary opportunity for vitamin D3 regulation. We tested the hypothesis that panther chameleons (Furcifer pardalis) behaviorally regulate exposure to UV in natural sunlight with high precision, accuracy, and effectiveness. Panther chameleons with low dietary vitamin D3 intake significantly increased exposure to UV in natural sunlight compared to those with high dietary vitamin D3 intake. All lizards fed low dietary vitamin D3 regulated within optimal UV levels with extreme effectiveness (ability to regulate within optimal UV levels relative to available UV). Chameleons of both dietary treatments regulated UV exposure with great precision, exhibiting little variation among individuals within treatments. Our results add to a growing body of literature that empirically demonstrates the importance of basking for nonthermoregulatory purposes and, more specifically, as an integral mechanism for the regulation of a vital hormone, vitamin D3.