Data from: Hold your breath beetle – mites!

Respiratory gas exchange in insects occurs via a branching tracheal system. The entrances to the air-filled tracheae are the spiracles, which are gate-like structures in the exoskeleton. The open or closed state of spiracles defines the three possible gas exchange patterns of insects. In resting insects, spiracles may open and close over time in a repeatable fashion that results in a discontinuous gas exchange (DGE) pattern characterized by periods of zero organism-to-environment gas exchange. Several adaptive hypotheses have been proposed to explain why insects engage in DGE, but none have attracted overwhelming support. We provide support for a previously untested hypothesis that posits that DGE minimises the risk of infestation of the tracheal system by mites and other agents. Here, we analyse the respiratory patterns of 15 species of ground beetle (Carabidae), of which more than 40% of individuals harboured external mites. Compared with mite-free individuals, infested one’s engaged significantly more often in DGE. Mite-free individuals predominantly employed a cyclic or continuous gas exchange pattern, which did not include complete spiracle closure. Complete spiracle closure may prevent parasites from invading, clogging, or transferring pathogens to the tracheal system or from foraging on tissue not protected by thick chitinous layers.昆虫的呼吸气体交换通过分支状的气管系统（tracheal system）完成。充气管的入口为气门（spiracles），即外骨骼（exoskeleton）上的门状结构。气门的开闭状态决定了昆虫三种可能的气体交换模式。在静息状态的昆虫中，气门会以可重复的节律反复开闭，由此产生不连续气体交换（DGE）模式，其特征为机体与环境间存在零气体交换的时段。目前已有多种适应性假说试图解释昆虫为何会采取不连续气体交换模式，但尚无一种假说获得广泛认可。本研究为此前未被验证的假说提供了支持：该假说认为不连续气体交换可降低螨类及其他生物侵染气管系统的风险。本研究分析了15种地甲（步甲科，Carabidae）的呼吸模式，其中超过40%的个体携带有外部螨类。与无螨个体相比，被侵染个体更频繁地表现出不连续气体交换模式。无螨个体主要采用循环式或连续式气体交换模式，该模式不存在气门完全关闭的阶段。气门完全关闭可阻止寄生虫侵染、堵塞气管系统，或向其传播病原体，同时也可避免寄生虫在未被厚几丁质层保护的组织上取食。