Meeting Abstract
93.5 Friday, Jan. 7 Panther chameleons behaviorally regulate optimal UV exposure depending on dietary vitamin D3 status KARSTEN, K.B.*; FERGUSON, G.W.; CHEN, T.C.; HOLICK, M.F.; Texas Christian University; Texas Christian University; Boston University Medical Center; Boston University Medical Center k.karsten@tcu.edu
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. In lizards, basking may be the primary opportunity for vitamin D3 regulation. We tested the hypothesis that panther chameleons (Furcifer pardalis) optimally regulate UV exposure based on dietary vitamin D via basking behavior. Panther chameleons with low dietary vitamin D3 significantly increased exposure to UV compared to those with high dietary vitamin D3. Lizards fed low dietary vitamin D3 regulated within optimal UV levels and with high precision, accuracy, and effectiveness. Our results add to a growing body of literature demonstrating the importance of basking for non-thermoregulatory purposes, and more specifically, as an integral mechanism for the regulation of a vital hormone. We discuss our results in light of recent findings of lizard extinctions on a massive scale due to global warming. Declines are not thought to be the result of increased heat stress, but rather from foraging limitations during periods of high energetic demand: they have less opportunity to forage before temperatures exceed a preferred upper limit. Lizards basking to regulate internal vitamin D face a dilemma: either avoid heat stress and become vitamin D deficient or optimally regulate vitamin D for development and reproduction and risk thermal death. Regulation of vitamin D homeostasis may present an additional survival challenge for some populations.
