Short-term temperature fluctuations show minimal effects on worker gut microbiota in Bombus terrestris under...

Insect symbionts are key contributors to many physiological traits of their hosts. The bumblebee microbiota is mainly composed of a few taxa that, although not necessary for their survival, present a long history of coevolution with their hosts, and contribute to their nutrition and defense against pathogens. Mutualistic interactions with endosymbionts can be affected by environmental factors, such as temperature. Bumblebees have the particularity of thermoregulating their nests, which might help the maintenance of these mutualisms. The aim of this study was to analyze how environmental temperature stress affects bumblebee's microbiota composition both within the nest environment and without the effect of colony thermoregulation. We exposed Bombus terrestris workers to environmental temperatures of 9 or 38 °C (within the range of temperatures of the species habitat) for five days, both within their original colonies and in small microcolonies. Then, we returned all workers to 28°C (control temperature) for five additional days to study if microbiota composition could be restored after thermal stress in case of changes. Analyses of microbiota composition indicated that temperature treatment had a significant effect on the workers, whereas the colony environment had a significant effect on the workers after the recovery period. Post-hoc analyses indicated that the heat treatment had a greater effect on microbiota composition than the cold treatment, but none of them were significant. Our results point to a robustness of bumblebee microbiota to temperature changes. Bumblebee symbionts could have adapted to temperature changes as a result of their exposure to very variable temperatures during queen hibernation, foraging, brood incubation and ex vivo phases outside nests.