The multidimensional nutritional niche of fungus-cultivar provisioning in free-ranging colonies of a neotropical leafcutter ant

Foraging trails of leafcutter colonies are iconic scenes in the Neotropics, with ants collecting freshly-cut plant fragments to provision a fungal food crop. We hypothesized that the fungus-cultivar’s requirements for macronutrients and minerals govern the foraging niche breadth of Atta colombica leafcutter ants. Analyses of plant fragments carried by foragers showed how nutrients from fruits, flowers, and leaves combine to maximize cultivar performance. While the most commonly foraged leaves delivered excess protein relative to the cultivar’s needs, in vitro experiments showed that the minerals P, Al, and Fe may expand the leafcutter foraging niche by enhancing the cultivar’s tolerance to protein-biased substrates. A suite of other minerals reduces cultivar performance in ways that may render plant fragments with optimal macronutrient blends unsuitable for provisioning. Our approach highlights how the nutritional challenges of provisioning a mutualist can govern the multidimensional realized niche available to a generalist insect herbivore.

切叶蚁群落的觅食路径是新热带区（Neotropics）的标志性景观：工蚁采集新鲜切割的植物碎屑，为其培育的食用真菌菌株提供营养储备。本研究假设，其所培育真菌菌株对大量营养素与矿物质的需求，决定了哥伦比亚切叶蚁（Atta colombica）的觅食生态位宽度。针对觅食工蚁携带的植物碎屑的分析显示，果实、花与叶片中的营养物质如何协同作用，以最大化真菌菌株的生长效能。尽管最常被采集的叶片相对于真菌菌株的需求存在蛋白质过剩的情况，但体外（in vitro）实验表明，磷（P）、铝（Al）与铁（Fe）等矿物质可通过提升真菌菌株对蛋白质过量基质的耐受性，拓宽切叶蚁的觅食生态位。另有一系列矿物质会降低真菌菌株的生长效能，使得具备最佳大量营养素配比的植物碎屑不再适合作为储备饲喂物。本研究方法揭示了，为互利共生伙伴提供营养所面临的挑战，如何调控这类广食性植食性昆虫可利用的多维实际生态位。