Meeting Abstract
Organisms fundamentally adjust their physiological state throughout their life-cycle and in response to predictable and unpredictable changes in their environment. Thyroid hormones (THs) play an important role in governing homeostatic processes in vertebrates through the control of gross metabolism and thermogenesis. Research suggests that TH concentrations reflect an individual’s metabolic expenditure; animals expending greater energy exhibit higher levels of circulating THs presumably to facilitate increased metabolic output. Data explicitly demonstrating the relationship between activity and TH levels in free-living animals is relatively sparse though TH levels are directly related to resting metabolic rate. We quantified above-ground activity and measured seasonal changes in plasma total T4 (TT4) and total T3 (TT3) across the short (3-5 mo) active season of female arctic ground squirrels. TT3 and TT4 became increasingly correlated across the active season, showing significant correlation only during weaning and early fattening. Female plasma TT4 was highest in the early season, while plasma TT3 peaked during lactation. TT3 was correlated with average time spent above ground during lactation, while TT4 was correlated with time above-ground during weaning and early fattening. These results suggest that circulating THs modulate activity of individuals, supporting an ecological context for seasonal changes in an individual’s physiological state. Integrating components of physiological state, such as hormone concentrations, and fine-scale information on activity provides insight into how free-living animals govern homeostatic processes across their annual cycle and in response to changes in environmental conditions.
