Cross-Resistance: A Consequence of Bi-partite Host-Parasite Coevolution.

Host-parasite coevolution can influence interactions of the host and parasite with the wider ecological community. One way that this may manifest is in cross-resistance towards other parasites, which has been observed to occur in some host-parasite evolution experiments. In this paper, we test for cross-resistance towards and in the red flour beetle , which was previously allowed to coevolve with the generalist entomopathogenic fungus . We combine survival and gene expression assays upon infection to test for cross-resistance and underlying mechanisms. We show that larvae of that evolved with under coevolutionary conditions were positively cross-resistant to the bacterium but not . Positive cross-resistance was mirrored at the gene expression level with markers that were representative of the oral route of infection being upregulated upon exposure. We find that positive cross-resistance towards evolved in as a consequence of its coevolutionary interactions with . This cross-resistance appears to be a consequence of resistance to oral toxicity. The fact that coevolution with results in resistance to but not implies that and may share mechanisms of infection or toxicity not shared by . This supports previous suggestions that may possess Cry-like toxins, similar to those found in , which allow it to infect orally.