Abstract

Living in a social group increases the risks of parasitism, especially in highly-related groups. In homogenous groups, with no reproductive division of labour, the impact of parasitism is unlikely to vary with host identity. Many social systems, however, do exhibit division of reproductive labour, most famously in social insects with their reproductive queens and generally infertile workers. In such systems, the impact of parasitism will differ for each group. Consequently, we predict that susceptibility to parasites will vary to reflect such differential impact. We tested this prediction using a trypanosome-bumble bee system, where Crithidia bombi infects both gynes and workers of Bombus terrestris. We studied both susceptibility to the parasite and relevant measures of the immune function. As predicted, gynes were significantly less susceptible to the parasite than workers, but while gynes and workers expressed different immune profiles, how these link to differential susceptibility remains unclear. In conclusion, our results suggest that differential selection pressures exerted by parasites may produce multiple phenotypes from a single genotype in order to maximise fitness in a social group context.

Significance statement

Social insect colonies dominate terrestrial ecology, and as such are targets for parasites. How they defend themselves against such threats is a key question. Here, we show that bumble bee gynes — the reproductive individuals that overwinter and found colonies in this annual social system — are more resistant to a parasite that disproportionately affects reproductive fitness than their sister workers. Differential patterns of susceptibility may help to explain the success of these social insects.

中文翻译：

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社会昆虫中雌性种姓的寄生虫抗性和免疫力

摘要

生活在一个社会群体中会增加寄生的风险，尤其是在高度相关的群体中。在没有生殖分工的同质群体中，寄生的影响不太可能随宿主身份而变化。然而，许多社会系统确实表现出生殖劳动的分工，最著名的是社会昆虫及其生殖女王和通常不育的工人。在这样的系统中，每个群体的寄生影响会有所不同。因此，我们预测对寄生虫的易感性会有所不同，以反映这种不同的影响。我们使用锥虫-大黄蜂系统测试了这一预测，其中Crithidia bombi感染Bombus terrestris的妇科动物和工人. 我们研究了对寄生虫的易感性和免疫功能的相关措施。正如预测的那样，女性对寄生虫的敏感性明显低于工人，但虽然女性和工人表达了不同的免疫特征，但这些与差异易感性的联系仍不清楚。总之，我们的结果表明，寄生虫施加的差异选择压力可能会从单一基因型产生多种表型，以最大限度地提高社会群体环境中的适应度。

意义陈述

社会性昆虫群落主导着陆地生态，因此是寄生虫的目标。他们如何保护自己免受此类威胁是一个关键问题。在这里，我们展示了大黄蜂 gynes——在这个一年一度的社会系统中越冬并发现殖民地的生殖个体——比它们的姊妹工蜂更能抵抗一种对生殖适应性影响不成比例的寄生虫。不同的易感性模式可能有助于解释这些群居昆虫的成功。