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

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Army ants are the top arthropod predators in tropical ecosystems. Besides their pivotal role as predators, a diverse fauna of animals, ranging from ant birds to arthropod symbionts, depends on the presence of army ants. For instance, several hundred species are obligate associates of the swarm-raiding army ant Eciton burchellii. The faunistic diversity of army ant guests entails major deficiencies in species identifications, mainly because the taxonomy of symbiont groups has remained untouched for decades. Notable among these groups are one of the most abundant and charismatic taxa: rove beetles of the genus Vatesus Sharp, 1876. The genus consists of 26 species. Their taxonomy has remained untouched since the latest revisions in the 1950s and 1960s. By modern standards, historical Vatesus species descriptions lack sufficient detail to capture phenotypic variation so that species identifications of Vatesus are problematic. Crucially, genitalia descriptions, which provide essential characters for beetle taxonomy, are missing for all but two species. The shaky taxonomy thus creates a serious impediment to any kind of research on these beetles. In the last years, I have compiled an extraordinary collection of Vatesus beetles, consisting of more than 1,600 specimens and at least 10 distinct species. Additionally, numerous museums have additionally accrued a huge number of specimens. Collectively, these collection efforts sum up to several thousand specimens covering a broad geographic area. Based on these remarkable collections and support of museums, it is my goal to achieve a modern systematic revision of Vatesus. The revision will be based on a multidisciplinary approach by combining the analyses of morphological characters and genetic loci (COI, wg, CAD). Clustering of genetic data will unveil possible candidate species. Representatives of each candidate species and all holotypes will then be scanned using synchrotron-generated X-ray microtomography (SRµCT), allowing for qualitative and quantitative analyses of beetles’ external and internal morphology. Importantly, using SRµCT I will analyze male and female genitalia without the need of specimen dissections, i.e. type material stays intact. Molecular and morphological data will be analyzed synergistically with the goal of robustly uncovering species boundaries and defining them based on anatomy. This integrative approach will provide a rigorous analysis of phenotypic and genetic variation of Vatesus beetles, which will result in detailed species descriptions that match the highest modern standards. Finally, I will create an easily usable dichotomous species key of Vatesus beetles by providing visual illustrations exemplifying the differences of presented characters via drawings, high-quality focus-stacked 2-D images, and 3-D models. A solid taxonomy and an easily usable species key will provide the foundation for any kind of future research on these enigmatic social insect symbionts.