Meeting Abstract
The aerobic capacity model of the evolution of endothermy posits that high basal metabolic rate (BMR), typical of endotherms, evolved as a correlated response to selection for high peak metabolic rate (PMR) elicited by e.g. locomotor activity bursts or thermogenesis. To test the model we studied 4 lines of laboratory mice artificially selected for high PMR elicited by swimming in water at 25 °C along with 4 control (randomly selected) lines. Our selection therefore affected both locomotor activity and metabolic response to sudden cold stress. Here, we compared thermogenic capacity and responses to short- and long-term exposure to low ambient temperature (4 °C) in selected mice and randomly bred controls. Selection significantly increased non-shivering thermogenesis (NST, elicited by epinephrine), but did not affect BMR nor the between line divergence in NST measured after acclimation to 4 °C. Likewise, although most studied physiological and behavioral traits (daily energy expenditure, core body temperature, spontaneous locomotor activity, markers of oxidative stress) were affected by ambient temperature, they were not modulated by selection. These patterns, together with the results of our earlier studies on mice divergently selected for BMR, suggest that significant increase in PMR may be not correlated with changes in many other fitness-related traits. Thus, the evolution of high BMR may reflect selection on traits other than PMR (e.g. high sustained metabolic rate during parental care). Financial support: National Science Centre, Poland, grant 2014/15/B/NZ8/00244 for P.B.
