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.

多伙伴互惠共生体系具有潜在的复杂动态特性，当某一共伴缺失或退居次要地位时，体系会产生补偿性响应。真菌种植蚁（切叶蚁族Attini）是担子菌（basidiomycete fungi）与产抗生素放线菌（antibiotic-producing actinomycete bacteria）的互惠共生伙伴；其培育的担子菌会受到专性寄生真菌（Escovopsis）以及多种广谱微生物的侵染。蚂蚁可借助放线菌与后胸侧板腺（metapleural glands, MGs）启动生化防御，并通过多样化的行为策略管控污染物。本研究以4种放线菌相对丰度存在差异的曲颚切叶蚁属（Trachymyrmex）物种为研究对象，以探究依赖于感染类型的各类抗菌策略间的相互作用机制。研究发现，后胸侧板腺梳理率与放线菌丰度呈负相关。两类后胸侧板腺梳理率较高或放线菌丰度较高的切叶蚁物种，对行为防御的投入相对较少；反之，两类生化防御投入相对有限的物种，则高度依赖行为防御策略。这种防御策略间的权衡关系表明，近缘物种可通过演化分化，针对同一威胁采用不同的防御机制。由此可见，细菌共生体与后胸侧板腺分泌物均非抵御专性寄生病原菌Escovopsis的必要防御手段，但降低其中一种防御模式的资源投入，往往会提升另一种防御模式的投入。