Pervasive effects of Wolbachia on host body mass and metabolic rate

Metabolic rate is a widely variable trait that reflects organismal energy expenditure. At least half of all arthropod species carry maternally transmitted Wolbachia bacteria, but it is poorly understood how these endosymbionts affect host physiology and fitness. We tested how two central host traits, body mass and standard metabolic rate (SMR), are altered by Wolbachia for nine diverse Drosophila fly species and 13 co-occurring Wolbachia variants diverged roughly 150 million years. Interspecific trait variation was structured according to the host phylogeny, but within each host system, Wolbachia almost always altered body mass and/or SMR. Wolbachia often caused increases or decreases in body mass that, in some cases, also led to mass-dependent effects on whole-organism SMR. Other Wolbachia altered mass-adjusted SMR. These variable effects are plausibly explained by complex interactions among Wolbachia and host genomes, as documented for other traits (e.g., Wolbachia -induced cytoplasmic incompatibility). Endosymbiont effects on body mass and metabolic rate likely have cascading consequences for host biology and evolution, because these central traits are correlated with many aspects of host physiology, behavior, and life history. This also applies to hosts transinfected with Wolbachia from Drosophila to reduce the impacts of pathogens and pests on multiple continents.