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Balancing selection for aflatoxin in Aspergillus flavus is maintained through interference competition with, and fungivory by insects

Milton Drott: Cornell University

<div>Mycotoxins contaminate large portions of world food supplies causing countless human deaths and incurring costs to growers. The role of mycotoxins in the ecology of the organisms that produce them remains poorly understood. This is even true of aflatoxin which, as one of the most potent and highly regulated mycotoxins, is also one of the most studied. Both aflatoxigenic and non-aflatoxigenic isolates of <em>Aspergillus flavus</em> are maintained by balancing selection, but the ecological function and impact of aflatoxin on fungal fitness is unknown. We hypothesize that balancing selection for aflatoxin production in <em>A. flavus </em>is driven by interaction with insects. To test this, we competed naturally occurring aflatoxigenic and non-aflatoxigenic field isolates of <em>A. flavus</em> with <em>Drosophila</em> larvae on medium containing 0-1750 ppb aflatoxin. We estimated fitness of <em>A. flavus</em> using qPCR to quantify its DNA. The addition of aflatoxin resulted in a 26-fold increase in fungal fitness between 0 and 1750 ppb. With no added toxin, aflatoxigenic isolates caused higher mortality of <em>Drosophila</em> larvae, and had higher fitness than non-aflatoxigenic isolates. Additionally, aflatoxin production increased an average of 1.5-fold in the presence of a single larva, and nearly 3-fold when the fungus was mechanically damaged. Our results provide the first clear evidence of a fitness advantage conferred to <em>A. flavus</em> by aflatoxin when interacting with insects and have implications for future research on strategies to control aflatoxin contamination.</div>

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