Lynch Zachary R, Schlenke Todd A, Morran Levi T, de Roode Jacobus C
Department of Biology, Emory University, Atlanta, Georgia, United States of America.
PLoS One. 2017 Jul 12;12(7):e0180182. doi: 10.1371/journal.pone.0180182. eCollection 2017.
As parasites coevolve with their hosts, they can evolve counter-defenses that render host immune responses ineffective. These counter-defenses are more likely to evolve in specialist parasites than generalist parasites; the latter face variable selection pressures between the different hosts they infect. Natural populations of the fruit fly Drosophila melanogaster are commonly threatened by endoparasitoid wasps in the genus Leptopilina, including the specialist L. boulardi and the generalist L. heterotoma, and both wasp species can incapacitate the cellular immune response of D. melanogaster larvae. Given that ethanol tolerance is high in D. melanogaster and stronger in the specialist wasp than the generalist, we tested whether fly larvae could use ethanol as an anti-parasite defense and whether its effectiveness would differ against the two wasp species. We found that fly larvae benefited from eating ethanol-containing food during exposure to L. heterotoma; we observed a two-fold decrease in parasitization intensity and a 24-fold increase in fly survival to adulthood. Although host ethanol consumption did not affect L. boulardi parasitization rates or intensities, it led to a modest increase in fly survival. Thus, ethanol conferred stronger protection against the generalist wasp than the specialist. We tested whether fly larvae can self-medicate by seeking ethanol-containing food after being attacked by wasps, but found no support for this hypothesis. We also allowed female flies to choose between control and ethanol-containing oviposition sites in the presence vs. absence of wasps and generally found significant preferences for ethanol regardless of wasp presence. Overall, our results suggest that D. melanogaster larvae obtain protection from certain parasitoid wasp species through their mothers' innate oviposition preferences for ethanol-containing food sources.
随着寄生虫与其宿主共同进化，它们会进化出反防御机制，使宿主的免疫反应失效。这些反防御机制在专性寄生虫中比在泛性寄生虫中更有可能进化；后者在它们感染的不同宿主之间面临可变的选择压力。果蝇黑腹果蝇的自然种群通常受到细蜂属内寄生蜂的威胁，包括专性的布氏细蜂和泛性的异腹细蜂，这两种黄蜂都能使黑腹果蝇幼虫的细胞免疫反应失效。鉴于黑腹果蝇的乙醇耐受性较高，且专性黄蜂比泛性黄蜂更强，我们测试了果蝇幼虫是否可以利用乙醇作为抗寄生虫防御手段，以及其有效性对这两种黄蜂是否会有所不同。我们发现，果蝇幼虫在接触异腹细蜂时食用含乙醇的食物会受益；我们观察到寄生强度降低了两倍，果蝇成年存活率提高了24倍。虽然宿主摄入乙醇并没有影响布氏细蜂的寄生率或强度，但它使果蝇存活率略有提高。因此，乙醇对泛性黄蜂的保护作用比对专性黄蜂更强。我们测试了果蝇幼虫在被黄蜂攻击后是否会通过寻找含乙醇的食物进行自我治疗，但没有找到支持这一假设的证据。我们还让雌蝇在有或没有黄蜂的情况下在对照产卵位点和含乙醇的产卵位点之间进行选择，结果发现无论是否有黄蜂，雌蝇通常都对乙醇有明显偏好。总体而言，我们的结果表明，黑腹果蝇幼虫通过其母亲对含乙醇食物来源的先天产卵偏好，获得了对某些寄生蜂物种的保护。
