BioProject

Virulence is a key trait under selection during host-parasite coevolution. In order to obtain increased fitness, parasites are predicted to increase their ability to circumvent and overcome host immunity. More...

Virulence is a key trait under selection during host-parasite coevolution. In order to obtain increased fitness, parasites are predicted to increase their ability to circumvent and overcome host immunity. A particular challenge for pathogens are external immune systems, found among various invertebrates. Such external immune systems are chemical defence systems comprised of highly potent antimicrobial compounds released by prospective hosts into the environment. We carried out a coevolution experiment with the entomopathogenic fungus, Beauveria bassiana, and the red flour beetle, Tribolium castaneum, which has a well-documented external immune system. Surprisingly, after just seven transfers of experimental evolution we saw a significant increase in virulence in all B. bassiana. This increase in virulence was mainly the result of the B. bassiana isolates evolving resistance to the external immune defences of the T. castaneum beetles, but not obviously through the increased production of toxins or other harmful substances. Furthermore, transcriptomic analyses of B. bassiana RNA-seq data implicates up-regulation of genes responsible for resistance to oxidative stress underlying the observed resistance. We conclude that external immunity acts as a powerful selective force for virulence evolution, with an increase in virulence being achieved apparently entirely by overcoming these defences, most likely due to elevated oxidative stress resistance. Overall design: mRNA profiles of Beauveria bassiana (ancestral: A and evolved isolates:BI5 & BI3) exposed to either 10µl of Methyl-para-benzoquinone (MBQ, quinone, 0.11µg per ml diluted in methanol) or methanol at 72h or 96h were generated by deep sequencing, in triplicate or single, using Illumina HiSeq2000. Less...