Meeting Abstract
Reproductive timing strongly influences the fitness of the individual. While most vertebrates rely on photoperiodic changes to induce seasonal puberty, the arctic ground squirrel (AGS) naturally undergoes reproductive maturation in a photoperiod-independent manner. In addition, males spontaneously activate their reproductive axis during hibernation, but the timing of puberty is sensitive to external cues. We are using electron microscopy to examine, define, and measure ultrastructural remodeling in pars tuberalis (PT) thyrotroph cells and anterior pituitary (AP) gonadotroph cells, as the AGS transitions from hibernation to the reproductive season. We are also quantifying how the morphology of endocrine cells corresponds with measures of reproductive axis outputs, including changes in steroidogenic gene expression in gonads and plasma sex steroid concentrations. Finally, we are examining the mechanisms that underly plasticity in hibernation phenology and examining whether AP activity can become dissociated from the PT signaling pathway by assessing cellular remodeling in males placed in a 30°C room during mid-hibernation, which induced early puberty onset. We hypothesize that changes in PT morphology underlie initiation of puberty and the timing of the end of hibernation in a photoperiod-independent manner. This basic system-level investigation of reproductive control mechanisms in the AGS could provide insight into non-photic mechanisms that induce puberty onset and underlie plasticity in pubertal timing.
