Response to ‘Commentary on Thoral et al. (2024) The relationship between mitochondrial respiration, resting metabolic rate and blood cell count in great tits’

Abstract

The commentary by Malkoc et al. highlights possible arguments explaining divergent findings of how mitochondrial metabolism in blood cells is related to whole-organism resting metabolic rate (RMR) in birds across the three studies that have addressed this relationship (Casagrande et al., 2023; Malkoc et al., 2021; Thoral et al., 2024). The authors argue that the lack of correlation between ROUTINE respiration in blood and RMR in Thoral et al. (2024), but the presence of such in their previous papers (Casagrande et al., 2023; Malkoc et al., 2021), can be explained by methodology (intact versus permeabilized blood cells), acclimation temperature, or the stress status of the individuals. In our response, we argue why the concerns expressed by Malkoc et al. should be interpreted with caution, and comment on the conclusions that can be drawn from studying both individual and mitochondrial metabolisms.