Data from: Dynamic disease management in Trachymyrmex fungus-growing ants (Attini: Formicidae)

Multipartner mutualisms have potentially complex dynamics, with compensatory responses when one partner is lost or relegated to a minor role. Fungus-growing ants (Attini) are mutualistic associates of basidiomycete fungi and antibiotic-producing actinomycete bacteria; the former are attacked by specialized fungi (Escovopsis) and diverse generalist microbes. Ants deploy biochemical defenses from bacteria and metapleural glands (MGs) and express different behaviors to control contaminants. We studied four Trachymyrmex species that differed in relative abundance of actinomycetes to understand interactions among antimicrobial tactics that are contingent on the nature of infection. MG grooming rate and actinomycete abundance were negatively correlated. The two species with high MG grooming rates or abundant actinomycetes made relatively little use of behavioral defenses. Conversely, the two species with relatively modest biochemical defenses relied heavily on behavior. Trade-offs suggest that related species can evolutionarily diverge to rely on different defense mechanisms against the same threat. Neither bacterial symbionts nor MG secretions thus appear to be essential for mounting defenses against the specialized pathogen Escovopsis, but reduced investment in one of these defense modes tends to increase investment in the other.

多伙伴共生体系（multipartner mutualisms）具备潜在的复杂动态特征，当其中某一共生伙伴缺失或退居次要功能地位时，体系会触发补偿响应。培养真菌的蚂蚁（切叶蚁族Attini）是担子菌（basidiomycete fungi）与产抗生素放线菌（antibiotic-producing actinomycete bacteria）的互利共生伙伴；这类真菌宿主会受到专性寄生真菌（Escovopsis属真菌）以及多种广谱微生物的侵染。蚂蚁可依托放线菌与后胸侧板腺（metapleural glands，MGs）产生的生化防御手段，并通过差异化行为策略来管控环境污染物。本研究选取了放线菌相对丰度存在显著差异的4种特拉希蜜蚁属（Trachymyrmex）蚂蚁，旨在探究依赖于感染类型的抗菌策略之间的相互作用关系。研究结果显示，后胸侧板腺清理速率与放线菌丰度呈显著负相关。其中，具备高后胸侧板腺清理速率或高丰度放线菌的两个物种，对行为防御的投入相对较少；与之相反，生化防御能力相对薄弱的两个物种，则高度依赖行为防御手段。这种防御策略的权衡效应表明，近缘物种可通过演化分异，针对同一类威胁采用截然不同的防御机制。由此可见，细菌共生体与后胸侧板腺分泌物均非针对专性病原菌Escovopsis属真菌发起防御的必需条件，但降低其中一类防御模式的资源投入，往往会提升另一类防御模式的投资强度。