Meeting Abstract

P2.120  Tuesday, Jan. 5  Diel Variation in Standard Metabolic Rate: Mediation by Photoperiod Cues and Melatonin? GAO, Sisi*; LUTTERSCHMIDT, William I.; LUTTERSCHMIDT, Deborah I.; The College of New Jersey; Sam Houston State University; Georgia State University lutterschmidt@shsu.edu

The hormone melatonin (N-acetyl-5-methoxytryptamine) synchronizes environmental factors, such as temperature and photoperiod, with physiological and behavioral processes. Increased melatonin concentrations function in lowering some physiological set points in diurnal but not nocturnal snakes. Results from previous research suggest that melatonin decreases standard metabolic rate (SMR) in a diurnal snake. In this study, we seek to establish bearded dragons (Pogona vitticeps) as a diurnal ectothermic model for investigating the role of melatonin and melatonin receptor-mediated responses in physiological rate processes and behavioral thermoregulation. We demonstrate that the SMR of this highly diurnal lizard varies significantly during a 12 h:12 h LD photoperiod. The SMR of Pogona vitticeps, held at constant body temperature, was significantly higher during mid-photophase than mid-scotophase. This observed diel variation in SMR may be associated with diel cycles of endogenous melatonin synthesis. A reverse 12 h:12 h LD photoperiod was used to investigate if the lower SMR during mid-scotophase can be entrained by photoperiod cues. Future experiments manipulating melatonin concentrations will confirm the role of melatonin in regulating SMR of Pogona vitticeps. Such baseline data will help establish Pogona vitticeps as an experimental model for future studies investigating how melatonin mediates temporal adjustments in physiology and behavior.