Data from: No evidence for behavioural adaptations to nematode parasitism by the fly Drosophila putrida

Behavioural adaptations of hosts to their parasites form an important component of the evolutionary dynamics of host–parasite interactions. As mushroom-feeding Drosophila can tolerate deadly mycotoxins, but their Howardula nematode parasites cannot, we asked how consuming the potent mycotoxin α-amanitin has affected this host–parasite interaction. We used the fly D. putrida and its parasite H. aoronymphium, which is both highly virulent and at high prevalence in some populations, and investigated whether adult flies utilize food with toxin to prevent infection in the next generation or consume the toxin to reduce the virulence of an already established infection. First, we found that uninfected females did not prefer to eat or lay their eggs on toxic food, indicating that selection has not acted on the flies to alter their behaviour towards α-amanitin to prevent their offspring from becoming infected by Howardula. However, we cannot rule out that flies use an alternate cue that is associated with toxin presence in the wild. Second, we found that infected females did not prefer to eat food with α-amanitin and that consuming α-amanitin did not cure or reduce the virulence of the parasite in adults that were already infected. In sum, our results indicate there are no direct effects of eating α-amanitin on this host–parasite interaction, and we suggest that toxin tolerance is more likely maintained by selection due to competition for resources than as a mechanism to avoid parasite infection or to reduce the virulence of infection.

宿主针对寄生虫的行为适应，是宿主-寄生虫互作演化动力学的重要组成部分。鉴于取食真菌的果蝇（Drosophila）可耐受致命真菌毒素，但其寄生的霍华德线虫（Howardula）却无法耐受此类毒素，本研究围绕摄入强效毒素α-鹅膏蕈碱（α-amanitin）会如何影响该宿主-寄生虫互作关系展开探究。我们以腐食果蝇（D. putrida）及其寄生线虫H. aoronymphium为实验材料——该线虫致死性强且在部分种群中具有较高流行率，旨在探究成年果蝇是否会通过取食含毒素的食物来阻止子代遭受寄生虫感染，或是通过摄入毒素以降低已建立感染的寄生虫的毒力。首先，研究发现未感染的雌蝇并不会优先选择在含毒素的食物上进食或产卵，这表明自然选择并未通过改变果蝇对α-鹅膏蕈碱的行为偏好，来帮助其子代规避霍华德线虫的感染。不过，本研究无法排除果蝇在自然环境中会利用与毒素存在相关的其他线索的可能性。其次，研究发现已感染的雌蝇并不会优先取食含α-鹅膏蕈碱的食物，且摄入该毒素既无法治愈已感染成虫体内的寄生虫，也不能降低其毒力。综上，本研究结果表明，摄入α-鹅膏蕈碱对该宿主-寄生虫互作关系并无直接影响；据此我们提出，果蝇对毒素的耐受性更可能是由资源竞争带来的自然选择所维持，而非作为规避寄生虫感染或降低感染毒力的适应性机制。