The influence of parasite load on transcriptional activity and morphology of a cestode and its ant intermediate host

Parasites with complex life cycles are known to induce phenotypic changes in their intermediate hosts to increase transmission to the final host. The magnitude of these changes could increase with the number of parasites, which would be beneficial to co-infecting parasites. Yet, adverse effects of high parasite load (i.e., many parasites in a single host) might stress both hosts and parasites (e.g., through an increased immune response). We investigated the consequences of parasite load on the transcriptional activity and morphology of the cestode Anomotaenia brevis and its intermediate host, the ant Temnothorax nylanderi. We demonstrated that many differentially expressed host genes shifted with parasite load, and their functions indicate a stronger immune response and fight against oxidative stress in heavily infected hosts. The expression of other host genes responded to infection in an all-or-nothing manner, as did the morphology of the host workers. However, the cestodes became smaller when they competed with other parasites for resources from a single host. Their expression profile further indicated shifts in host immune avoidance, starvation resistance and vesicle-mediated transport. In summary, our study reveals clear consequences of parasite load and highlights specific processes and traits affected by this.

具有复杂生活周期的寄生虫已被证实可诱导其中间宿主产生表型变化，从而提升向终末宿主传播的效率。此类变化的程度可能随寄生虫数量的增加而加剧，这对共感染的寄生虫而言是有利的。然而，高寄生虫负荷（即单个宿主体内寄生大量寄生虫）所带来的负面影响，可能会通过增强免疫应答等途径，同时给宿主与寄生虫带来应激压力。我们探究了寄生虫负荷对绦虫Anomotaenia brevis及其中间宿主——蚂蚁Temnothorax nylanderi的转录活性与形态学特征的影响。研究证实，宿主体内大量差异表达基因的表达水平随寄生虫负荷发生改变，其功能富集结果显示，重度感染宿主的免疫应答与抗氧化应激通路被显著激活。其余宿主基因的表达模式呈现全有或全无的响应特征，宿主工蚁的形态变化亦符合这一规律。但当绦虫在单一宿主体内与其他寄生虫竞争资源时，其个体体型会显著减小。绦虫的表达谱进一步显示出宿主免疫逃逸、饥饿抗性以及囊泡介导转运等相关通路的变化。综上，本研究清晰揭示了寄生虫负荷所带来的显著影响，并着重阐明了受其调控的特定生物学过程与性状特征。