The active mouse rests within: Energy management among and within individuals

1. The relationship between daily energy expenditure (DEE) and resting metabolic rate (RMR) provides insight into how organisms allocate energy to maintenance versus energetically expensive activities such as locomotor activity.

2. Three models have been devised to describe energy management: the allocation, independent, and performance models, which respectively predict a DEE-RMR slope of b<1, b=1, and b>1.

3. Here, we took paired repeated metabolic and behavioural measurements in 51 female white-footed mice to 1) evaluate which energy management models apply at the among- and within-individual levels, and to 2) quantify the relationship between metabolic traits and two energetically expensive behaviours.

4. The DEE-RMR slope was different at the among- versus within-individual levels, with values supporting the performance and allocation models at the among- and within-individual levels, respectively. Accordingly, the relationship between voluntary wheel running and RMR was positive at the among-individual level (r = 0.40±0.21), but negative at the within-individual level (r ­= -0.23±0.10).

5. To our knowledge, this is the first study to simultaneously partition the relationship between RMR and behaviour at the among- versus within-individuals levels while determining which energy management models apply at each of these levels. In doing so, we have identified a mechanism through which compensation occurs at the within-individual level.

Methods
See paper.