Meeting Abstract

87.1  Friday, Jan. 7  Photosensitivity of the circadian clock is correlated with photic niche in Anolis lizards MOORE, A.F.*; MENAKER, M.; University of Virginia, Charlottesville; University of Virginia, Charlottesville

The evolutionary forces that have shaped the organization of the vertebrate circadian system are unknown. It has been postulated that photic niche exerts selective pressure on the circadian system, such that the clock is adapted to the predominant light cues in the microhabitat. We tested this hypothesis using Puerto Rican Anolis lizards, which have diverged into multiple photic niches. We predicted that the magnitude of a light-induced phase shift would be negatively correlated with the photic intensity of the microhabitat. A flow-through culture system allowed us to measure circadian output from an isolated circadian oscillator—the pineal gland—in two pairs of sister species: 1) A. cristatellus (full sun) and A. gundlachi (full shade), and 2) A. pulchellus (full sun) and A. krugi (partial shade). Pineal glands were exposed to a light-dark cycle, with a two-hour pulse of bright light administered during the early night before release into constant darkness. Radioimmunoassay was used to quantify the amount of pineal melatonin released into the culture medium at timed intervals. We found significant phase differences among species, although there were no differences in free-running period. The treatment caused a significant phase-delay in A. gundlachi but not in A. cristatellus, supporting our hypothesis. There was no significant phase shift in A. pulchellus; in A. krugi, the light treatment disrupted melatonin rhythmicity. These results suggest that the circadian clocks of shade-dwelling Anolis species are more sensitive to the effects of light, consistent with the hypothesis that photic niche divergence leads to changes in circadian photoreception.