Circannual transitions in gene expression: lessons from seasonal adaptations.

Circannual timing is important for the coordination of seasonal activities, particularly promoting the survival of individuals in adverse conditions through adaptive physiological and behavioral changes. This includes optimizing the survival of offspring by coordinating reproductive efforts at appropriate times. Thus, timing is very important for overall fitness. In this chapter, we provide several examples of circannually timed events, including mammalian hibernation, discussing the physiological changes that accompany these events, and some of the known genes and pathways underlying these changes. We then describe five candidate systems that are potentially involved in circannual timing. Finally, we discuss several recent advances in molecular biology and animal husbandry that have made the use of nonmodel organisms for research more feasible, which will hopefully promote and encourage further advancement in the knowledge of circannual timing.