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.

培菌蚁族（Attini）已演化出与担子菌（basidiomycete fungus）的专性依赖关系，它们将该真菌作为食物进行栽培。鲜为人知的是，诸多菌蚁物种还会利用这种栽培真菌覆盖自身的卵、幼虫及蛹。
这种护幼覆盖行为的适应性功能意义至今仍未得到充分阐明。针对该行为，有一项假说认为：当数千只姊妹工蚁紧密群居，且幼虫与蛹无法像蜜蜂、胡蜂那样通过巢室获得保护，同时自身又处于静止状态时，这种覆盖行为属于病原体防护体系的一部分。
我们针对切叶蚁（Acromyrmex echinatior）的护幼覆盖行为开展了行为学观察，并对蛹体上的菌丝覆盖层进行了实验性移除处理，随后将蛹体暴露于虫生真菌（entomopathogenic fungus）布氏绿僵菌（Metarhizium brunneum）中，以此验证该覆盖层在病原体抗性中是否发挥作用。
我们的研究结果显示，工蚁主动进行的菌丝护幼覆盖是一种具有行为可塑性的性状，其表现会随时间、生命阶段及蚁群品级的不同而发生变化。相较于实验性移除了菌丝覆盖层或天然未被菌丝覆盖的蛹体，带有真菌覆盖层的蛹体，其分生孢子（conidia）出现速率以及产生病原孢子的蛹体表面占比均有所降低。携带菌丝的感染蛹体存活率高于未携带覆盖层的感染蛹体，但这一结果取决于成年姊妹工蚁与蛹体互动的时间节点。最后，相较于带有菌丝的感染蛹体，工蚁会对未携带菌丝的感染蛹体更频繁地进行后胸腺（metapleural gland）梳理行为。
我们的研究结果表明，菌丝护幼覆盖或许在抑制病原体生长及后续病害传播方面发挥着重要作用，从而为蚁群的防御体系增添了一层全新的保护机制。