Raw and processed data.

Plants and fungi often produce toxic metabolites, but herbivores and fungivores that evolve resistance to these toxins gain access to underutilized resources. An additional benefit of living in and consuming toxins is that animals can gain protection against non-resistant predators and parasites. The fruit fly Drosophila melanogaster consumes yeasts growing on rotting fruit and has evolved resistance to toxic fermentation products such as ethanol and acetic acid. We tested whether acetic acid protects flies from one of their most common natural enemies, parasitoid wasps, which infect fly larvae and pupae. We found that both wasp parasitism rate and wasp eclosion success are reduced when fly larvae are grown on acetic acid food, and wasp mothers actively avoid infecting fly larvae reared in acetic acid food if given a choice. In each case, acetic acid results in a greater fitness cost for a generalist parasitoid compared to a specialist parasitoid. Furthermore, fly mothers sense the presence of parasitoids in their environment and alter their oviposition behavior to lay eggs in more acetic acid-heavy food when wasps were present. This demonstrates that flies perceive the competing costs to their offspring of wasp parasitism and acetic acid toxicity but balance those costs to maximize offspring fitness.

植物与真菌通常会产生有毒代谢物，而对这些毒素演化出抗性的草食动物与食真菌动物，则得以利用未被充分开发的资源。此外，栖息于毒素环境并摄食毒素的动物，还能获得针对非抗性捕食者与寄生虫的防御能力。黑腹果蝇（Drosophila melanogaster）以腐烂果实上生长的酵母菌为食，并已演化出对乙醇、乙酸等有毒发酵产物的抗性。本研究开展实验，探究乙酸能否保护果蝇免受其最常见的自然天敌之一——寄生蜂（parasitoid wasps）——的侵害，这类寄生蜂会感染果蝇幼虫与蛹。研究发现，当果蝇幼虫在添加乙酸的饲养培养基中生长时，寄生蜂的寄生率与羽化成功率均有所降低；且若存在选择余地，寄生蜂雌成虫会主动避开在乙酸培养基中饲养的果蝇幼虫进行寄生。在所有实验场景中，相较于专食性寄生蜂，广食性寄生蜂因乙酸暴露而承受的适合度成本更高。此外，果蝇雌成虫能够感知环境中寄生蜂的存在，并调整产卵行为：当寄生蜂存在时，果蝇会将卵产在乙酸含量更高的培养基中。这一结果表明，果蝇能够权衡子代面临的寄生蜂寄生风险与乙酸毒性的双重代价，并通过平衡二者以最大化子代的适合度。