Abstract
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 Bacillus thuringiensis and Pseudomonas entomophila in the red flour beetle Tribolium castaneum, which was previously allowed to coevolve with the generalist entomopathogenic fungus Beauveria bassiana. We combine survival and gene expression assays upon infection to test for cross-resistance and underlying mechanisms. We show that larvae of T. castaneum that evolved with B. bassiana under coevolutionary conditions were positively cross-resistant to the bacterium B. thuringiensis, but not P. entomophila. Positive cross-resistance was mirrored at the gene expression level with markers that were representative of the oral route of infection being upregulated upon B. bassiana exposure. We find that positive cross-resistance towards B. thuringiensis evolved in T. castaneum as a consequence of its coevolutionary interactions with B. bassiana. This cross-resistance appears to be a consequence of resistance to oral toxicity. The fact that coevolution with B. bassiana results in resistance to B. thuringiensis, but not P. entomophila implies that B. thuringiensis and B. bassiana may share mechanisms of infection or toxicity not shared by P. entomophila. This supports previous suggestions that B. bassiana may possess Cry-like toxins, similar to those found in B. thuringiensis, which allow it to infect orally.
Highlights
In nature, hosts are likely to exist within a complex community and interact with multiple parasites [1,2,3]
Our results indicate that cross-resistance evolved towards B. thuringiensis as a consequence of coevolution with B. bassiana and that cross resistance is potentially due to a shared route of infection between
Survival of F2 larvae of generation 13 beetles from the coevolution experiment was recorded for a period of 7, 10, and 30 days post exposure to, B. thuringiensis, P. entomophila, and B. bassiana, respectively
Summary
Hosts are likely to exist within a complex community and interact with multiple parasites [1,2,3]. Many host-parasite coevolution experiments attempt to understand the dynamics [14,15], adaptations [16,17,18], and underlying genetic mechanisms [16,19,20,21] of host responses in the context of the parasite it coevolved with. Such evolutionary interactions can impact host traits important in the wider context of its environment [22]. Larvae of Drosophila melanogaster evolved with the parasitoid
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