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 is 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 0-2000 ppb aflatoxin, using qPCR 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 3-fold 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 provide the first clear evidence of a fitness advantage conferred to A. flavus by aflatoxin when interacting with insects.微生物次级代谢产物对其产生菌的生态学功能仍未被充分阐明。黄曲霉（Aspergillus flavus）产黄曲霉毒素的性状变异由平衡选择维持，但该化合物的生态学功能及其对真菌适合度的影响仍属未知。我们提出假说：黄曲霉的黄曲霉毒素产毒性状所受的平衡选择，源于其与昆虫的相互作用。为验证该假说，我们在含0~2000 ppb黄曲霉毒素的培养基上，将天然分离得到的产毒与非产毒真菌分离株与果蝇（Drosophila）幼虫进行竞争实验，并以qPCR定量黄曲霉DNA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。未添加毒素时，产毒分离株会导致果蝇幼虫更高的死亡率，且其适合度略高于非产毒分离株。此外，当存在单只果蝇幼虫时，黄曲霉毒素的产量平均提升1.5倍；当真菌受到机械损伤时，产量增幅接近3倍。我们认为，黄曲霉毒素在抗真菌取食中的作用，与其在干扰竞争中的功能密不可分。本研究结果首次明确证实，在与昆虫相互作用时，黄曲霉毒素可赋予黄曲霉适合度优势。