Respirometry data for cactus mice (Peromyscus eremicus) corresponding to Colella et al. 2021

Metabolism is a complex phenotype shaped by natural environmental rhythms,
as well as behavioral, morphological, and physiological adaptations.
Metabolism has been historically studied under constant environmental
conditions, but new methods of continuous metabolic phenotyping now offer
a window into organismal responses to dynamic environments, and enable
identification of abiotic controls and the timing of physiological
responses relative to environmental change. We use indirect calorimetry to
characterize metabolic phenotypes of the desert-adapted cactus mouse
(Peromyscus eremicus) in response variable environmental conditions that
mimic their native environment versus those recorded under constant warm
and constant cool conditions, while using a constant photoperiod and full
access to resources. We found significant sexual dimorphism, with males
being more prone to dehydration than females. Under circadian
environmental variation, most metabolic shifts occurred prior to physical
environmental change and the timing was disrupted under both constant
temperature-humidity treatments. The ratio of CO2 produced to O2 consumed
(the respiratory quotient) reached greater than 1.0, only during the light
phase under diurnally variable conditions, a pattern that strongly
suggests that lipogenesis is contributing to the production of energy and
endogenous water. Our results are consistent with historical descriptions
of circadian torpor in this species (torpid by day, active by night), but
reject the hypothesis that torpor is initiated by food restriction or
negative water balance.