Date of Award

5-2020

Document Type

Thesis

Department

Biology

First Advisor

Aaron Schirmer, Ph.D.

Abstract

Circadian rhythms are generated by internal biological clocks of organisms and are responsible for the synchronization of an organism’s external and internal environment. The cells responsible for conducting and maintaining the circadian system are known to be coupled in order to maintain a harmonic rhythm. Desynchronization of the master circadian rhythm can cause the presence of two or more rhythms to emerge in a single organism, also known as splitting behavior. Photopollution and artificial light is known to disrupt this synchronization and result in a desynchronized or split rhythm. Many studies have highlighted that photopollution can disrupt the biological clock suggesting that artificial light may have a positive correlation with the splitting of the circadian behavioral rhythms in mice. This thesis will present a brief overview of the cellular and neurological basis for circadian rhythms and what is known about the synchronization of circadian clocks throughout the body. In the present study, locomotor activity and circadian behavior were analyzed to highlight patterns of circadian desynchronization and its relationship to photopollution. Specifically, previously collected data on the circadian locomotor activity rhythms of C57BL/6J mice exposed to 0, 6, 20, and 32 lux levels of night time light were analyzed and the splitting behavior was quantified. We hypothesized that photopollution will have a positive correlation with the splitting of the circadian behavioral rhythms in mice. It was discovered that increasing levels of night time light positively correlated with increased splitting behavior. The individual rhythmic component tau varied across light levels and a significant decrease in amplitude was found as the level of night time light increased. Analysis of the emerging secondary rhythms highlight a significant difference in period iv and power with increasing levels of night time light. These results support the correlation between photopollution and splitting behavior of circadian rhythms. This research has important implications for both wildlife and humans, specifically the inhabitants of urban environments that are inundated with artificial light putting their circadian system at risk of desynchrony.

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