Wolbachia-infected pharaoh ant colonies have higher egg production, metabolic rate, and worker survival

Wolbachia is a widespread endosymbiotic bacteria with diverse phenotypic
effects on its insect hosts, ranging from parasitic to mutualistic.
Wolbachia also commonly infects social insects, where it faces unique
challenges associated with its hosts’ caste-based reproductive division of
labor and colony living. Here we dissect the benefits and costs of
Wolbachia infection on life-history traits of the invasive pharaoh ant,
Monomorium pharaonis. Pharaoh ants are relatively short-lived and show
natural variation in Wolbachia infection between colonies, thereby making
them an ideal model system for this study. We quantified effects on the
lifespan of queen and worker castes, the egg-laying rate of queens across
queen lifespan, and the metabolic rates of whole colonies and colony
members. Newly-infected queens laid more eggs than uninfected queens but
had similar metabolic rates and lifespans. Surprisingly, infected workers
outlived uninfected workers. At the colony level, infected colonies were
more productive due to increased queen egg-laying rates and worker
longevity, and infected colonies had higher metabolic rates during peak
colony productivity. While some effects of infection, such as elevated
colony-level metabolic rates may be detrimental in more stressful natural
conditions, we did not find any costs of infection under relatively benign
laboratory conditions. Overall, our study emphasizes the beneficial
effects of Wolbachia on colony-level growth and metabolism in this
species.