INRAE, Oniris, BIOEPAR, 44300, Nantes, France; Department of Biology and Biotechnology "L. Spallanzani", University of Pavia, Pavia, Italy.
INRAE, Oniris, BIOEPAR, 44300, Nantes, France.
Ticks Tick Borne Dis. 2021 Jul;12(4):101707. doi: 10.1016/j.ttbdis.2021.101707. Epub 2021 Mar 18.
Ticks harbour rich and diverse microbiota and, among the microorganisms associated with them, endosymbionts are the subject of a growing interest due to their crucial role in the biology of their arthropod host. Midichloria mitochondrii is the main endosymbiont of the European tick Ixodes ricinus and is found in abundance in all I. ricinus females, while at a much lower density in males, where it is even absent in 56 % of the individuals. This endosymbiont is also known to increase in numbers after the blood meal of larvae, nymphs or females. Because of this difference in the prevalence of M. mitochondrii between the two sexes, surveying the density of these bacteria in nymphs that will become either females or males could help to understand the behaviour of Midichloria in its arthropod host. To this aim, we have set up an experimental design by building 3 groups of unfed nymphs based on their scutum and hypostome lengths. After engorgement, weighing and moulting of a subset of the nymphs, a significant difference in sex-ratio among the 3 groups was observed. In parallel, Midichloria load in individual nymphs was quantified by qPCR both before and after engorgement. No difference in either body mass or Midichloria load was observed at the unfed stage, but following engorgement, both features were significantly different between each size group. Our results demonstrate that symbiont dynamics during nymphal engorgement is different between the two sexes, resulting in a significantly higher Midichloria load in nymphs that will become females. The consequences of those findings on our understanding of the interplay between the endosymbiont and its arthropod host are discussed.
蜱虫体内携带着丰富多样的微生物群落，其中，内共生体由于在节肢动物宿主生物学中具有重要作用而成为研究热点。中白体（Midichloria mitochondrii）是欧洲璃眼蜱（Ixodes ricinus）的主要内共生体，在所有雌性璃眼蜱中大量存在，而在雄性中密度要低得多，甚至有 56%的个体中不存在该共生体。已知这种内共生体在幼虫、若虫或雌性蜱虫吸血后数量会增加。由于雌雄蜱虫中 M. mitochondrii 的流行率存在差异，因此对即将成为雌性或雄性的若虫中这些细菌的密度进行调查，有助于了解 Midichloria 在其节肢动物宿主中的行为。为此，我们通过建立 3 组未进食的若虫组，根据它们盾板和口下板的长度来设计实验。在一组若虫饱食、称重和蜕皮后，观察到 3 组之间的性比存在显著差异。同时，通过 qPCR 对个体若虫的 Midichloria 负荷进行定量，分别在饱食前和饱食后进行。在未进食阶段，体重和 Midichloria 负荷没有差异，但饱食后，每个大小组之间的这两个特征都存在显著差异。我们的结果表明，在若虫饱食期间，内共生体动态在雌雄之间存在差异，导致即将成为雌性的若虫中 Midichloria 负荷显著增加。讨论了这些发现对我们理解内共生体与其节肢动物宿主相互作用的影响。
