Data from: Fitness in invasive social wasps: the role of variation in viral load, immune response and paternity in predicting nest size and reproductive output

Within any one habitat, the relative fitness of organisms in a population can vary substantially. Social insects like the common wasp are among the most successful invasive animals, but show enormous variation in nest size and other fitness-related traits. Some of this variation may be caused by pathogens such as viruses that can have serious consequences in social insects, which range from reduced productivity to colony death. Both individual immune responses and colony-level traits such as genetic diversity are likely to influence effects of pathogen infections on colony fitness. Here we investigate how infections with Kashmir Bee Virus (KBV), immune response and intracolony genetic diversity (due to queen polyandry) affect nest size in the invasive common wasp, Vespula vulgaris. We show that KBV is highly prevalent in wasps and expression of antiviral immune genes is significantly increased with higher viral loads across individuals. Patriline membership within a nest did not influence KBV susceptibility or immune response. A permutational MANCOVA revealed that polyandry, viral load, and expression of the immune gene Dicer were significant predictors of variation in nest size. High intracolony genetic diversity due to polyandry has previously been hypothesized to improve colony-level resistance to parasites and pathogens. Consistent with this hypothesis, we observed genetically diverse colonies to be significantly larger and to produce more queens, although this effect was not driven by the pathogen we investigated. Invasive wasps clearly suffer from pathogens and expend resources, as indicated here by elevated immune gene expression, toward reducing pathogen-impact on colony fitness.

在同一栖息地内，种群中生物个体的相对适合度往往存在显著差异。诸如普通黄胡蜂（common wasp）在内的社会性昆虫是最成功的入侵性动物类群之一，但它们的巢穴大小及其他与适合度相关的性状却存在显著变异。这类变异的部分诱因可能是病毒等病原体：它们对社会性昆虫可造成严重危害，轻则降低种群生产力，重则导致整个蜂群覆灭。个体免疫反应与蜂群层面的性状（如遗传多样性）均可能影响病原体感染对蜂群适合度的作用效果。本研究针对入侵性物种普通黄胡蜂（Vespula vulgaris），探讨克什米尔蜜蜂病毒（Kashmir Bee Virus, KBV）感染、免疫反应以及蜂群内遗传多样性（源于蜂王多雄交配）对其巢穴大小的影响。研究结果表明，KBV在胡蜂种群中传播极为广泛，且个体的抗病毒免疫基因表达量随病毒载量升高而显著上调。巢穴内的父系群归属并不会影响胡蜂对KBV的易感性或免疫反应。通过置换多元协方差分析（permutational MANCOVA）发现，蜂王多雄交配、病毒载量以及免疫基因Dicer的表达量均为巢穴大小变异的显著预测因子。此前有假说提出，蜂王多雄交配所带来的高蜂群内遗传多样性，可提升蜂群对寄生虫与病原体的群体抗性。本研究结果与该假说一致：遗传多样性更高的蜂群不仅巢穴体积显著更大，还能产生更多新蜂王，不过这一效应并非由本研究涉及的病原体所介导。正如本研究中免疫基因表达上调所揭示的那样，入侵性胡蜂确实会受到病原体的侵害，并会消耗资源以减轻病原体对蜂群适合度的负面影响。