Meeting Abstract

P1.74  Sunday, Jan. 4  Photic Niche and Photosensitivity of the Pineal Oscillator in Anolis Species MOORE, A.M.**; BARRY, B.D.; MENAKER, M.; University of Virginia; University of Virginia; University of Virginia afm4z@virginia.edu

Circadian clocks coordinate behavior and physiology such that events occur at the appropriate time of day or night. Light is the most salient cue by which the clock is entrained to the 24-hr day, yet the influence of environmental light on clock evolution remains largely unexplored. To investigate the relationship between photic niche and the physiology of a circadian pacemaker, we have focused on the lizard pineal gland because a) it is intrinsically photosensitive and entrains to light directly, b) its role as a circadian pacemaker varies widely across species, and c) its rhythmic output, melatonin, is readily quantifiable. We cultured individual pineal glands from several species of Anolis lizards and measured melatonin output under lighting regimes designed to reveal period, amplitude, and photosensitivity of the pineal oscillator. We show that light suppresses nighttime melatonin levels in all species except A. carolinensis, with considerable variation among species in the magnitude and duration of suppression. Preliminary analyses suggest that shade-dwelling species are more sensitive to light-induced melatonin suppression than are sun-dwelling species, providing initial support for the hypothesis that photic niche is correlated with circadian photosensitivity. Future work will incorporate additional species in an attempt to characterize the contributions of phylogenetic lineage, structural niche, photic niche, and light history effects towards phenotypic variation in circadian physiology.