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Systematic revision of the army ant-symbiont beetle genus Vatesus Sharp, 1876 (Staphylinidae: Tachyporinae: Vatesini) based on a multidisciplinary approach

Subject Area Systematics and Morphology (Zoology)
Term from 2016 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 310785848
 
Final Report Year 2024

Final Report Abstract

Early naturalists such as Darwin and Bates were captivated by the hordes of army ants that roamed the forest floor in search of living prey. The evolutionary biologist Huxley aptly referred to them as the Huns and Tartars of the insect world. From a modern, ecological standpoint, army ants are essential components of tropical rainforests as they act as top invertebrate predators, likely exerting top-down control on prey populations. Further, army ants promote local biodiversity because a multitude of species seeks contact with them, including birds that feed on invertebrates flushed out by their raids, parasitic arthropods that consume their prey or their brood, and other arthropods that scavenge in their refuse deposits. While generations of researchers have studied army ant associated insects, systematic inventories at the community level were virtually absent. Over several years, we collected arthropod guests of all potential host army ants of the genus Eciton at one study site, La Selva Biological Station in Costa Rica. We determined species boundaries of army ant guests based on morphological characters and genetic analyses. With 117 beetle species, 11 fly species, one millipede species, and one silverfish species we uncovered an immense diversity of guests accumulating around army ant colonies. Among these, we formally described 12 new species and recognized many more undescribed species. We deposited hundreds of specimens at museum collections, facilitating future research on these remarkable creatures. Our findings further revealed that associations with army ants ranged from facultative leaf litter scavengers found in refuse deposits to symbiotic, host-dependent guests that live as inquilines within the colonies of a single host species. We demonstrated that several phenotypic traits facilitate social integration and minimize aggression towards these inquilines. For example, we observed a correlation between the guests’ body size and the level of host aggression received, with diminutive forms experiencing fewer attacks. In summary, our research unveiled a remarkable legion of invertebrate species seeking contact with army ants, and we uncovered several traits that enable successful host exploitation in symbiotic guests. However, like many inhabitants of tropical ecosystems, this legion faces threats due to severe human interference with the natural world. Given that army ants are sensitive to habitat degradation, their local extinction would undoubtedly trigger an extinction cascade affecting numerous specialized, host-specific species, including the diverse fauna of obligate guests. To safeguard army ants and their marvellous symbiotic fauna for future generations, it is imperative to intensify efforts to protect tropical rainforests.

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