Institute of Organismic and Molecular Evolutionary Biology, Johannes-Gutenberg University of Mainz, Mainz, Germany.
Institut de Recherche sur la Biologie de l'Insecte, UMR 7261, CNRS, Université de Tours, Tours, France.
Int J Parasitol. 2020 Jun;50(6-7):461-469. doi: 10.1016/j.ijpara.2020.01.007. Epub 2020 Mar 26.
Studying the costs and benefits of host-parasite interactions is of central importance to shed light on the evolutionary drivers of host life history traits. Although gregarines (Apicomplexa: Sporozoa) are one of the most frequent parasites in the gut of invertebrates, the diversity of its potential impacts on a host remains poorly explored. In this study, we addressed this gap in knowledge by investigating the prevalence of natural infections by the gregarine Gregarina ovata and testing how these infections shape a large set of morphological, behavioural and physiological traits in the European earwig Forficula auricularia. Our results first show that G. ovata was present in 76.8% of 573 field-sampled earwigs, and that its prevalence was both higher in males compared with females and increased between July and September. The load of G. ovata in the infected individuals was higher in males than females, but this sex difference vanished during the season. Our experiments then surprisingly revealed apparent benefits of G. ovata infections. Food-deprived hosts survived longer when they exhibited high compared with low gregarine loads. Moreover, the presence of gregarines was associated with a reduced phenoloxidase activity, indicating a lower immune resistance or a higher immune tolerance of the infected hosts. By contrast, we found no effect of G. ovata presence and number on earwigs' development (eye distance, forceps length), activity, food consumption or resistance against a fungal pathogen. Overall, our findings suggest that G. ovata could be involved in a mutualistic relationship with the European earwig. Given the ubiquitous presence of gregarines among invertebrates, our data also suggest that this common member of insect gut flora could have a broad and positive role in the life history of many host species.
研究宿主-寄生虫相互作用的成本和收益对于揭示宿主生活史特征的进化驱动因素至关重要。虽然疟原虫（孢子虫门：孢子虫）是无脊椎动物肠道中最常见的寄生虫之一，但它们对宿主的潜在影响的多样性仍未得到充分探索。在这项研究中，我们通过调查天然感染疟原虫 Gregarina ovata 的流行情况，并测试这些感染如何塑造欧洲耳虫 Forficula auricularia 的一系列形态、行为和生理特征，来填补这一知识空白。我们的研究结果首先表明，G. ovata 存在于 573 只野外采样的耳虫中的 76.8%，其流行率在雄性中高于雌性，并且在 7 月至 9 月之间增加。感染个体中 G. ovata 的负荷在雄性中高于雌性，但这种性别差异在季节期间消失了。我们的实验出人意料地揭示了 G. ovata 感染的明显好处。与低疟原虫负荷相比，食物匮乏的宿主在表现出高疟原虫负荷时存活时间更长。此外，疟原虫的存在与酚氧化酶活性降低有关，表明感染宿主的免疫抵抗力降低或免疫耐受性增加。相比之下，我们没有发现 G. ovata 的存在和数量对耳虫的发育（眼距、钳子长度）、活动、食物消耗或对真菌病原体的抗性有影响。总的来说，我们的研究结果表明，G. ovata 可能与欧洲耳虫存在互利关系。鉴于疟原虫在无脊椎动物中普遍存在，我们的数据还表明，这种昆虫肠道菌群中的常见成员可能在许多宿主物种的生活史中发挥广泛而积极的作用。
