Locomotor activity of mice divergently selected for basal metabolic rate: a test of hypotheses on the evolution of endothermy

The aerobic capacity model postulates that high basal metabolic rates (BMR) underlying endothermy evolved as a correlated response to the selection on maximal levels of oxygen consumption ( [graphic removed] ) associated with locomotor activity. The recent assimilation capacity model specifically assumes that high BMR evolved as a by-product of the selection for effective parental care, which required long-term locomotor activity fuelled by energy assimilated from food. To test both models, we compared metabolic and behavioural correlates in males of laboratory mice divergently selected on body mass-corrected BMR. [graphic removed] elicited by running on the treadmill did not differ between selection lines, which points to the lack of genetic correlation between BMR and [graphic removed] . In contrast, there was a positive, genetic correlation between spontaneous long-term locomotor activity, food intake and BMR. Our results therefore corroborate predictions of the assimilation capacity model of endothermy evolution.