Environment, Brain, and Behavior: Neuroendocrine mechanisms underlying seasonal rhythms in stress, immunity, and the gut microbiota in Siberian hamsters (Phodopus sungorus)

Author

Elyan Shor

Date

2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Biology

Committee Chair

David Freeman

Abstract

The daily axial rotation of the Earth and its annual orbit around the sun both result in recurring fluctuations in geophysical cycles, thus creating cyclic changes in environmental factors. Organisms that can anticipate these environmental changes and adapt appropriately may maximize their survival and fitness. Such adaptations manifest themselves as biological rhythms: rhythmic shifts in physiology and behavior that match rhythmic shifts in environmental conditions. Among the most predictable environmental cues in temperate regions is the annual progression of changes in day length, and the capacity to measure and respond to seasonal changes in the light cycle is termed photoperiodism. Siberian hamsters (Phodopus sungorus) are robustly seasonal: they express multiple readily observable changes in physical, physiological, and behavioral outputs, and are thus an ideal model in the study of photoperiodism. Although the broad mechanics of photoperiodism have been well-documented, neither the exact neuroendocrine mechanisms governing seasonal rhythms in behavior and physiology, nor their relationships to each other and to the environment, have been fully characterized. Thus, the goal of the present research was to clarify these interactions by investigating the links between photoperiod, brain, physiology, gut microbiota, and behavior. First, we investigated the neuroendocrine pathway underlying photoperiodic physiology, and found that the paraventricular thalamus is necessary in regulating seasonal alterations in stress and immunity. We then investigated the relationship between photoperiod, brain, and the gut microbiota, and found that seasonal shifts in the microbiota are driven by the pineal gland. Finally, we investigated the relationship between the gut microbiota and seasonal behavior, finding that the gut microbiota plays an essential role in the seasonal expression of aggression. Altogether, the present research connects photoperiod to the brain, the brain to physiology, and physiology to behavior, while also opening promising new avenues of investigation regarding each of these relationships. This research represents an important advance in our understanding of photoperiodism, our understanding of biological rhythms, and ultimately, our understanding of how animals interact with their environments.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to ProQuest

Recommended Citation

Shor, Elyan, "Environment, Brain, and Behavior: Neuroendocrine mechanisms underlying seasonal rhythms in stress, immunity, and the gut microbiota in Siberian hamsters (Phodopus sungorus)" (2021). Electronic Theses and Dissertations. 2775.
https://digitalcommons.memphis.edu/etd/2775