Mitochondrial genetic effects mediate the response to stress through development, but not adult metabolic rate in Drosophila

Energy expenditure is fundamental to physiology, behaviour, ecology, and life history, yet the mechanisms that regulate metabolic rate remain poorly understood. At the cellular level, incompatibilities between the maternally inherited mitochondrial genome and the nuclear genome can impair energy production, signalling and gene expression, with potential to disrupt a wide range of physiological processes. However, how these often-subtle genomic mismatches influence whole-organism traits such as metabolic rate, activity, and fitness remains unclear. Here, we generated mitonuclear-mismatched fly lines to test how early-life dietary and metabolic stress affect larval and adult physiology. Our results revealed sex and line-specific physiological effects, with larval development, survival and female fertility strongly contingent on the haplotypes and treatment, while adult resting metabolic rate and activity were not influenced by mitochondrial haplotype, nor by developmental stress.