Date of this Version
Walker, J. (2019.) Diurnal Corticosterone Variations Across Seasons in Ornate Box Turtles (Terrapene ornata ornata). Undergraduate Honors Thesis. University of Nebraska-Lincoln.
Many organisms have developed strategies for surviving harsh winter conditions. Hypothermia has emerged as an adaptive behavior to combat low temperatures and limited resources associated with the cold season. Adaptive hypothermia exploits decreased metabolism, oxygen intake, and decreased physiological functioning in order to more efficiently conserve energy. Corticosterone is a well-known hormone associated with energy and metabolism regulation. Levels of corticosterone vary daily in correspondence with varying metabolic rate. Little is currently known about how corticosterone levels differ between active seasons and winter dormancy when many organisms (specifically ectotherms) undergo extensive periods of low metabolic activity. This study examined how corticosterone levels varied in ornate box turtles, Terrapene ornata ornata. Blood samples were collected from twenty ornate box turtles during both active and inactive seasons. Plasma corticosterone levels were determined and statistical analyses were performed to test how concentrations changed over the 24-hour period as well as across seasons. Our results showed that there is a significant variation in corticosterone levels during hibernation and suggested a circadian rhythm during summer. A strong trend was also found in corticosterone levels across the two seasons. These results indicate that significant changes are made to metabolism and energy regulation between active months and hibernation. This study helps to better understand glucocorticoid variations over the course of the 24-hour period as well as how ectotherms respond to seasonal changes–both topics that have not been extensively studied previously.