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

The role of microbial secondary metabolites in the ecology of the organisms that produce them remains poorly understood. Variation in aflatoxin production by Aspergillus flavus is maintained by balancing selection, but the ecological function and impact on fungal fitness of this compound are unknown. We hypothesize that balancing selection for aflatoxin production in A. flavus is driven by interaction with insects. To test this, we competed naturally occurring aflatoxigenic and non-aflatoxigenic fungal isolates against Drosophila larvae on medium containing 0–1750 ppb aflatoxin, using quantitative PCR to quantify A. flavus DNA as a proxy for fungal fitness. The addition of aflatoxin across this range resulted in a 26-fold increase in fungal fitness. With no added toxin, aflatoxigenic isolates caused higher mortality of Drosophila larvae and had slightly 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 threefold when the fungus was mechanically damaged. We argue that the role of aflatoxin in protection from fungivory is inextricably linked to its role in interference competition. Our results, to our knowledge, provide the first clear evidence of a fitness advantage conferred to A. flavus by aflatoxin when interacting with insects.

微生物次生代谢产物（microbial secondary metabolites）对其产生宿主的生态学功能至今仍未得到充分阐释。黄曲霉（Aspergillus flavus）所产黄曲霉毒素（aflatoxin）的产量变异由平衡选择所维持，但该化合物的生态学功能及其对真菌适合度的影响尚不明确。我们提出假说：黄曲霉中维持黄曲霉毒素合成的平衡选择，源自其与昆虫的相互作用。为验证该假说，我们将天然分离得到的产毒与非产毒黄曲霉菌株与果蝇幼虫置于含有0至1750 ppb黄曲霉毒素的培养基中开展竞争实验，并通过定量PCR（quantitative PCR）定量黄曲霉DNA，以此作为真菌适合度的替代评价指标。在此浓度范围内添加黄曲霉毒素，可使真菌适合度提升26倍。在未添加毒素的条件下，产毒株会导致更高的果蝇幼虫死亡率，且其适合度略高于非产毒株。此外，当体系中存在单只果蝇幼虫时，黄曲霉毒素的产量平均提升1.5倍；而当真菌受到机械损伤时，毒素产量则提升近3倍。我们认为，黄曲霉毒素在抵御食真菌作用中的功能，与其在干扰竞争中的作用密不可分。据我们所知，本研究结果首次明确证实了黄曲霉毒素在与昆虫互作时，可为黄曲霉带来显著的适合度优势。