Data from: Slowing them down will make them lose: a role for attine ant crop fungus in defending pupae against infections?

Fungus-growing ants (Attini) have evolved an obligate dependency upon a basidiomycete fungus that they cultivate as their food. Less well known is that the crop fungus is also used by many attine species to cover their eggs, larvae and pupae.
The adaptive functional significance of this brood covering is poorly understood. One hypothesis to account for this behaviour is that it is part of the pathogen protection portfolio when many thousands of sister workers live in close proximity and larvae and pupae are not protected by cells, as in bees and wasps, and are immobile.
We performed behavioural observations on brood covering in the leaf-cutting ant Acromyrmex echinatior and we experimentally manipulated mycelial cover on pupae and exposed them to the entomopathogenic fungus Metarhizium brunneum to test for a role in pathogen resistance.
Our results show that active mycelial brood covering by workers is a behaviourally plastic trait that varies temporally, and across life stages and castes. The presence of a fungal cover on the pupae reduced the rate at which conidia appeared and the percentage of pupal surface that produced pathogen spores, compared to pupae that had fungal cover experimentally removed or naturally had no mycelial cover. Infected pupae with mycelium had higher survival rates than infected pupae without the cover, although this depended upon the time at which adult sister workers were allowed to interact with pupae. Finally, workers employed higher rates of metapleural gland grooming to infected pupae without mycelium than to infected pupae with mycelium.
Our results imply that mycelial brood covering may play a significant role in suppressing the growth and subsequent spread of disease, thus adding a novel layer of protection to their defence portfolio.

培育真菌的蚂蚁（切叶蚁亚科Attini）已演化出与一种担子菌（basidiomycete fungus）的专性共生关系——它们将该真菌作为食物进行栽培。鲜为人知的是，多数切叶蚁物种还会利用该栽培真菌覆盖自身的卵、幼虫与蛹态个体。
该抚育覆盖行为的适应性功能意义迄今仍未得到充分阐释。有假说提出，当数千只姊妹工蚁紧密聚居时，且幼虫与蛹既不像蜂类、胡蜂那样受巢室保护，自身又无法移动，那么这种覆盖行为便属于病原体防护体系的组成部分。
我们针对切叶蚁物种棘颚切叶蚁（Acromyrmex echinatior）的抚育覆盖行为开展了行为学观察，并对蛹体表面的菌丝覆盖层进行实验操控，将处理后的蛹体暴露于虫生真菌（entomopathogenic fungus）布氏绿僵菌（Metarhizium brunneum）环境中，以此验证该菌丝覆盖层在病原体抗性中所起到的作用。
研究结果显示，工蚁主动为抚育对象覆盖菌丝的行为属于一种行为可塑性性状，其表达会随时间进程、昆虫生命阶段以及蚁类品级发生变化。相较于实验去除菌丝覆盖层或天然无菌丝覆盖的蛹体，带有真菌覆盖层的蛹体，其分生孢子（conidia）出现率以及产生病原体孢子的蛹体表面积占比均有所降低。感染布氏绿僵菌的蛹体若带有菌丝覆盖层，其存活率高于无覆盖层的感染蛹体，但该效应受限于允许姊妹工蚁与蛹体互动的时间节点。最后，相较于带有菌丝覆盖层的感染蛹体，工蚁会对无菌丝覆盖的感染蛹体实施更高频率的后胸侧板腺（metapleural gland）清洁行为。
本研究结果表明，菌丝抚育覆盖行为或许在抑制病原体生长及后续疾病传播方面发挥着重要作用，从而为蚁类的防御体系新增了一层保护机制。