Meeting Abstract

P3.179  Sunday, Jan. 6  Diel rhythm of plasma corticosterone in White’s treefrog, Litoria caerulea KAISER, K.*; JONES, C.G.; MARENTES, A.A.; WEICKUM, R.M.; SALTZMAN, W.; Univ. of California, Riverside kristinekaiser@gmail.com

Although widely thought of as stress hormones, glucocorticoids have myriad functions, and in most organisms are secreted in a diel cycle. The circadian rhythm of circulating corticosterone (CORT) concentrations has been characterized in several amphibians; however, treefrogs (family Hylidae) have been generally overlooked, despite the variety of CORT studies performed on this species-rich group of frogs. We characterized the pattern of basal circulating CORT concentrations over the 24-hour cycle in White’s treefrogs (Litoria caerulea). We sampled blood by cardiac puncture once per week from nine male, captive-reared frogs from October to December, 2011, with six collection time points over the course of the day. Plasma was extracted and CORT levels were determined using a radioimmunoassay kit that was validated for this species. We found that male L. caerulea exhibit a diel rhythm, with a significant trough at the 08:30 h sample and a slight peak at 12:30 h. CORT levels in L. caerulea were lower than those observed in most other amphibians; however, sampling occurred outside of the breeding season, when circulating CORT levels generally are lower in frogs, and a repeat of this study during the breeding season when social stimuli are present would likely yield higher basal levels. We provide the first characterization of the CORT diel rhythm in a hylid frog, and suggest that such data provide an important foundation for proper interpretation of any stress or CORT study.