A distinct infection cost associated with trans-generational priming of antibacterial immunity in bumble-bees.

The adaptive value of facultative maternal adjustment of offspring immunity, or trans-generational immune-priming, will depend on the ecological background. In particular, where there is a mismatch between the immune adjustment and offspring environment, the immunological link between mothers and offspring may be disadvantageous owing to the presence of associated costs. Costs to an individual of responding to an immune challenge are extensively documented. However, in addition to parents, the relevant costs for trans-generational immune-priming also pertain to offspring, but as yet it is unknown what costs offspring will bear. In bumble-bees, higher antibacterial activity has been shown as a trans-generational effect when mothers receive a bacterial-based immune challenge prior to colony founding. Here we show that while naive offspring from immune-challenged mothers do not show evidence for a direct energy-related survival cost, they do show increased susceptibility to a parasite distinctly unrelated to the maternal challenge. The presence of costs associated with trans-generational immune-priming will shape the evolution of this trait depending on the ecological setting.