Torpor energetics are related to the interaction between body mass and climate in bats of the family Vespertilionidae

Torpor is an adaptive strategy that allows animals to cope with energy limitations under adverse environmental conditions. In birds and mammals, intrinsic and extrinsic factors such as body mass (Mb) and ambient temperature (Ta) are well established triggers of torpor. Interestingly, the interplay between Mb and climate with different Ta on torpor traits in bats remains unexplored. Using open flow respirometry, we calculated Ta upon entering torpor (Tat), the reduction in torpid metabolic rate relative to the basal metabolic rate (TMRred), the Ta at which torpor metabolic rate reached its minimum (Ta adjust), and minimum torpid metabolic rate (TMRmin) in 11 bat species of the family Vespertilionidae that differ in Mb from warm and cold climates. We also included TMRmin data retrieved through a bibliography review. We tested the effects of Mb and climate on torpor traits using mixed-effect phylogenetic models. All models showed a significant interaction between Mb and climate. This interaction was inversely related to Tat, TMRred, Ta adjust, and positively related to TMRmin. These results are likely explained by the differences in Mb and the metabolic rate of bats from different climates, which may allow individuals to express torpor in places with different Ta. Further studies to assess torpor use in bats of different climates are proposed. Summary statementThe interaction between body mass and climate influences torpor energetics in bats of the family Vespertilionidae. As a result, torpid traits change based on body mass and climate.