DISSERTATION RESEARCH: Ecological Correlates of Circadian Organization: Photic Niche and Photosensitivity in Anolis Lizards

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Circadian clocks, found in virtually all organisms from bacteria to humans, control daily rhythms in physiology and behavior, including the familiar sleep-wake cycle. The day-night cycle synchronizes the circadian clock to the external world. Light is crucial for the proper timing of circadian rhythms, yet organisms live in diverse light habitats, ranging from dark caves to sun-drenched savannahs. How does the circadian clock respond "correctly" to this broad range of light cues? This project tests the hypothesis that circadian clocks have been modified by evolution such that they respond appropriately to light levels normally experienced by a species in its native habitat. To test this idea, the investigators will capture several different species of anoles, small Caribbean lizards living in diverse light conditions. Using automated behavioral recording techniques, they will determine how behavioral activity rhythms change according to the strength of the light-dark cycle. The investigators will also examine the pineal gland, a small organ located in the brain that secretes a hormone called melatonin. The pineal gland is the master circadian clock in lizards, and melatonin production is controlled by light. By measuring the light-induced changes in melatonin production, the investigators can determine the photic (light) sensitivity of the circadian clock. The prediction is that anole species living in the deep forest will be more sensitive to the effects of light on the circadian clock, relative to species living in sunnier habitats. Understanding the evolutionary relationship between the light environment and circadian clocks is important from a conservation standpoint, as "light pollution" from urban settlements is known to disrupt ecosystems. This project will provide research experience for several undergraduate students, in addition to the doctoral training of at least one graduate student.