Vogelweith Fanny, Moreau Jérôme, Thiéry Denis, Moret Yannick
Université de Bourgogne, Equipe Ecologie-Evolution, UMR 6282 Biogéosciences, 6 Bd Gabriel, F-21000 Dijon, France; INRA, UMR 1065 Save ISVV, B.P.81, F-33883 Villenave d'Ornon Cedex, France; Université de Bordeaux, Bordeaux Sciences Agro, INRA, UMR 1065 Save ISVV, B.P.81, F-33883 Villenave d'Ornon Cedex, France.
Université de Bourgogne, Equipe Ecologie-Evolution, UMR 6282 Biogéosciences, 6 Bd Gabriel, F-21000 Dijon, France.
J Insect Physiol. 2015 Jun;77:55-61. doi: 10.1016/j.jinsphys.2015.04.003. Epub 2015 Apr 23.
Inherent to the cost of immunity, the immune system itself can exhibit tradeoffs between its arms. Phytophagous insects face a wide range of microbial and eukaryotic parasites, each activating different immune pathways that could compromise the activity of the others. Feeding larvae are primarily exposed to microbes, which growth is controlled by antibiotic secondary metabolites produced by the host plant. The resulting variation in abundance of microbes on plants is expected to differentially stimulate the insect antimicrobial immune defenses. Under the above tradeoff hypothesis, stimulation of the insect antimicrobial defenses is expected to compromise immune activity against eukaryote parasites. In the European grape berry moth, Eupoecilia ambiguella, immune effectors directed towards microbes are negatively correlated to those directed towards eukaryotic parasites among host plants. Here, we hypothesize this relationship is caused by a variable control of the microbial community among host plants by their antibiotic metabolites. To test this hypothesis, we first quantified antimicrobial activity in berries of several grape varieties. We then measured immune defenses of E. ambiguella larvae raised on artificial diets in which we mimicked levels of antimicrobial activity of grape berries using tetracycline to control the abundance of growing microbes. Another group of larvae was raised on artificial diets made of berry extracts only to control for the effect of nutrition. We found that controlling microbe abundance with tetracycline in diets did not explain variation in the immune function whereas the presence of berry extracts did. This suggests that variation in immune defenses of E. ambiguella among grape varieties is caused by nutritional difference among host plants rather than microbe abundance. Further study of the effects of berry compounds on larval immune parameters will be needed to explain the observed tradeoff among immune system components.
由于免疫成本的内在因素，免疫系统本身在其各个组成部分之间可能会表现出权衡。植食性昆虫面临着各种各样的微生物和真核寄生虫，每种寄生虫都会激活不同的免疫途径，而这些途径可能会相互影响。取食的幼虫主要接触微生物，微生物的生长受寄主植物产生的抗生素次生代谢产物控制。植物上微生物丰度的这种变化预计会以不同方式刺激昆虫的抗菌免疫防御。在上述权衡假说下，刺激昆虫的抗菌防御预计会损害其针对真核寄生虫的免疫活性。在欧洲葡萄浆果蛾（Eupoecilia ambiguella）中，寄主植物中针对微生物的免疫效应物与针对真核寄生虫的免疫效应物呈负相关。在这里，我们假设这种关系是由寄主植物通过其抗生素代谢产物对微生物群落的可变控制引起的。为了验证这一假说，我们首先对几个葡萄品种的浆果中的抗菌活性进行了量化。然后，我们测量了在人工饲料上饲养的欧洲葡萄浆果蛾幼虫的免疫防御能力，在这些人工饲料中，我们使用四环素模拟葡萄浆果的抗菌活性水平，以控制生长中的微生物数量。另一组幼虫仅在由浆果提取物制成的人工饲料上饲养，以控制营养的影响。我们发现，在饲料中用四环素控制微生物数量并不能解释免疫功能的差异，而浆果提取物的存在却能解释。这表明欧洲葡萄浆果蛾在不同葡萄品种间免疫防御的差异是由寄主植物间的营养差异而非微生物数量引起的。需要进一步研究浆果化合物对幼虫免疫参数的影响，以解释观察到的免疫系统各组成部分之间的权衡。
