Data from: A multi-faceted approach testing the effects of previous bacterial exposure on resistance and tolerance

1. Hosts can alter their strategy towards pathogens during their lifetime,
i.e., they can show phenotypic plasticity in immunity or life history.
Immune priming is one such example, where a previous encounter with a
pathogen confers enhanced protection upon secondary challenge, resulting
in reduced pathogen load (i.e. resistance) and improved host survival.
However, an initial encounter might also enhance tolerance, particularly
to less virulent opportunistic pathogens that establish persistent
infections. In this scenario, individuals are better able to reduce the
negative fitness consequences that result from a high pathogen load.
Finally, previous exposure may also lead to life history adjustments, such
as terminal investment into reproduction. 2. Using different Drosophila
melanogaster host genotypes and two bacterial pathogens, Lactococcus
lactis and Pseudomonas entomophila, we tested if previous exposure results
in resistance or tolerance and whether it modifies immune gene expression
during an acute-phase infection (one day post-challenge). We then asked if
previous pathogen exposure affects chronic-phase pathogen persistence and
longer-term survival (28 days post-challenge). 3. We predicted that
previous exposure would increase host resistance to an early stage
bacterial infection while it might come at a cost to host fecundity
tolerance. We reasoned that resistance would be due in part to stronger
immune gene expression after challenge. We expected that previous exposure
would improve long-term survival, that it would reduce infection
persistence, and we expected to find genetic variation in these responses.
4. We found that previous exposure to P. entomophila weakened host
resistance to a second infection independent of genotype and had no effect
on immune gene expression. Fecundity tolerance showed genotypic variation
but was not influenced by previous exposure. However, L. lactis persisted
as a chronic infection, whereas survivors cleared the more pathogenic P.
entomophila infection. 5. To our knowledge, this is the first study that
addresses host tolerance to bacteria in relation to previous exposure,
taking a multi-faceted approach to address the topic. Our results suggest
that previous exposure comes with transient costs to resistance during the
early stage of infection in this host-pathogen system and that infection
persistence may be bacterium-specific.