Data from: lactation at hot temperature: a test of heat dissipation limitation in mice divergently selected for BMR

The HDL (Heat Dissipation Limitation) hypothesis posits that mammalian
energy budgets (SuSMR, Sustained Metabolic Rate) are limited by the
ability to dissipate metabolic heat. The HDL hypothesis has often been
tested in lactating mice but rarely in females, systematically differing
in SuSMR. Here, we used lines of laboratory mice divergently selected for
Basal Metabolic Rate (BMR) and effectively co-selected for SuSMR. We
exposed lactating females to 23°C and 30°C and manipulated their heat
dissipation abilities by fur shaving. Exposure to 30°C did not affect the
high BMR mice' litter mass but increased litter mass in the low BMR
mice. Fur shaving did not affect litter mass. However, it decreased body
temperature (Tb) by 0.2°C in the shaved mice, independent of line
affiliation and ambient temperature. In both lines exposed to 30°C, the Tb
increased by 0.2°C, while Daily Energy Expenditures (DEEs - a proxy of
SuSMR) decreased by 20% and still was higher in the high BMR mice. These
results do not support the HDL hypothesis. Low SuSMR individuals may
benefit from higher ambient temperatures because of reduced costs of
thermoregulation. It may change the course of natural selection towards
reducing SuSMR and BMR.