Meeting Abstract
Reproductive timing strongly influences the fitness of individuals. While most vertebrates rely on changes in daylength to induce seasonal reproduction, the arctic ground squirrel (AGS) naturally undergoes reproductive maturity in a photoperiod-independent manner. In addition, male AGS spontaneously activate their reproductive axis during hibernation, but the timing of hibernation and reproduction are sensitive to external cues. We hypothesize that changes in pars tuberalis (PT) thyrotroph morphology underlie hibernation and reproductive phenology in a photoperiod-independent manner. We used electron microscopy to examine, define, and measure ultrastructural remodeling in PT thyrotroph cells, hypothalamic tanycytes, and pars distalis (PD) gonadotroph cells, as the AGS transitioned from hibernating to reproductively active. We also quantified how cell morphology corresponds with measures of reproductive axis outputs, including changes in sex steroid gene expression and development in the gonads, and plasma steroid concentrations. Finally, we examined mechanisms that underlie plasticity in hibernation and reproduction phenology, and whether hypothalamic and PD activity can become dissociated from the PT signaling pathway by assessing cellular remodeling in males placed in a 30°C room during mid-winter, which induces early reproductive onset. This basic system-level investigation of reproductive control mechanisms may inform researchers on how cell ultrastructure influences connections between neuroendocrine circuits and the role these play in triggering puberty onset.
