Data from: Ant societies buffer individual-level effects of parasite infections

Parasites decrease host fitness and can induce changes in host behavior, morphology, and physiology. When parasites exploit social insects, they influence not only infected individuals but the society as a whole. Workers of the ant Temnothorax nylanderi are an intermediate host for the cestode Anomotaenia brevis. We studied a heavily parasitized population and found that while parasite infection had strong and diverse consequences for individual workers, colony fitness remained unchanged. On the individual level, we uncovered differences among the three worker types: infected and healthy workers from parasitized colonies and healthy workers from non-parasitized colonies. Infected workers were smaller than healthy ones and had, as parasite load increased, smaller heads. Behavioral changes extended to all workers from parasitized colonies, which were less active but groomed more. Healthy workers from parasitized colonies showed behavioral patterns intermediate to those of infected workers and healthy workers from non-parasitized colonies. Despite the lower activity level, an important fitness parameter - per-worker productivity - remained unaltered in parasitized colonies. However, the investment strategies of parasitized colonies changed as their sex ratio became male-biased and male body size increased. In short, ant colonies can buffer the drain of resources by the parasite despite strong effects on individual workers.

寄生虫可降低宿主适合度（host fitness），并可诱导宿主在行为、形态与生理层面发生改变。当寄生虫侵染社会性昆虫（social insects）时，其影响不仅局限于受感染个体，更会波及整个蚁群社会。尼兰德扁胸蚁（Temnothorax nylanderi）的工蚁是异带绦虫（Anomotaenia brevis）的中间宿主（intermediate host）。本研究针对重度寄生的蚁群种群开展调查，结果显示：尽管寄生虫感染对单个工蚁产生了强烈且多样的影响，但蚁群适合度（colony fitness）并未发生改变。在个体层面，研究团队发现三类工蚁存在显著差异：寄生蚁群中的受感染工蚁、寄生蚁群中的健康工蚁，以及非寄生蚁群中的健康工蚁。受感染工蚁的体型小于健康工蚁，且随着寄生负荷（parasite load）的升高，其头部尺寸也逐渐缩小。寄生蚁群中的所有工蚁均出现行为改变：其活动活跃度更低，但理毛频率更高。寄生蚁群中的健康工蚁，其行为模式介于受感染工蚁与非寄生蚁群中的健康工蚁之间。尽管工蚁活跃度有所下降，但一项关键的适合度参数——单工蚁生产力（per-worker productivity）——在寄生蚁群中并未发生改变。然而，寄生蚁群的资源投资策略发生了变化：其种群性比（sex ratio）偏向雄性，且雄性个体的体型也有所增大。简言之，尽管寄生虫对单个工蚁造成了显著影响，但蚁群能够缓冲寄生虫所带来的资源损耗。