Hibernation

To survive during harsh environmental conditions including scarce food availability, animals developed strategies to survive. Animals that can travel long distances by air or water can migrate. Some that cannot travel long distances evolved the ability to hibernate. Some of these animals are ground squirrels.

During hibernation (up to seven months), ground squirrels cycle between a state of torpor interspersed with brief periods of interbout arousals (IBA). Torpor is characterized by a drastic reduction in body temperature accompanied by decreased heart, respiration and metabolic rates, blood pressure and overall activity. Animals remain in this state for up to two weeks at a time. Torpor bouts are interrupted by IBAs, that are a temporary state in which ground squirrels restore all of their physiological processes to levels seen in active squirrels.

I study the sexual maturation process in the thirteen-lined ground squirrel (Ictidomys tridecemlineatus). This process is interrupted and delayed when animals experience starvation, dehydration and prolonged cold exposure. Thirteen-lined ground squirrels hibernate without access to food and water in cold temperatures for up to seven months. Recently, we reported that juvenile ground squirrels activate their reproductive axis during their very first hibernation season and initiate sexual maturation despite depletion of internal reserves and long-term hypothermia. Through a temporal analysis of hibernation, I found that the reproductive axis in the brain becomes active. Additionally, production of sexual hormones is increased during IBAs and gonadal growth also happens. This activation occurs independently of physiological state and food availability and involves activation of central and peripheral components of the reproductive axis.

The mechanisms that ground squirrels employ to initiate sexual maturation during hibernation are not well understood. Through a multidisciplinary approach, I aim to answer this question.