No support for socio‐physiological suppression effect on metabolism of paired white mice ( Mus sp.)

1. Three experiments were performed on white mice (strain MF1) to establish if there was social or physiological suppression of metabolism, mediated by elevated ambient levels of CO 2 , when animals were in close contact. In the first two experiments the metabolism of two mice were each measured solitarily and paired together in the same chamber, both with and without a partition that allowed visual, auditory and olfactory communication but restricted physical contact. 2. Comparisons were made between the sum of the two solitary measurements, and the observed measurements of paired individuals. In the first experiment air flow was low and ambient CO 2 was always at levels predicted to produce suppression (> 0·2%), independent of whether the animals were measured alone or paired. 3. The paired mice had greater metabolism than expected from the sum of their solitary metabolic rates whether the partition was present or absent. This increase was due to increased activity of the animals when in pairs. This experiment indicated that when CO 2 levels were maintained in the range 0·2–0·5% there was no social suppression of metabolism. 4. In experiment 2 metabolic rates were measured of solitary mice exposed to subthreshold levels of CO 2 (≈ 0·12%) and paired mice that experienced levels above the supposed threshold (≈ 0·24%). Again the observed metabolism of the paired mice exceeded the sum of their metabolic rates when solitary. The increase was also attributable to greater activity of the animals in pairs. 5. This experiment indicated no social suppression effect when CO 2 varied in the range 0·12–0·24%. Moreover there was no significant difference between the oxygen consumptions of mice in experiment 2 compared with experiment 1, indicating that independent of the social context there was no suppressive effect of increases in CO 2 concentration over the range 0·12–0·5% CO 2 . 6. Finally, in experiment 3, when two mice were placed in sequential separate chambers (allowing no social contact), their summed metabolism did not differ from the sum of their solitary measurements when a CO 2 absorber was placed in the airflow linking the chambers. When the CO 2 absorber was absent the observed metabolism of the pair exceeded the sum of the solitary measurements. 7. Overall, across all three experiments no evidence was found for either a social or a physiological suppression of metabolism mediated via CO 2 (0·12–0·5%).