A defensive body plan was pre-adaptive for termitophily in the rove beetle tribe Termitohospitini (Staphylinidae: Aleocharinae)

<jats:title>Abstract</jats:title><jats:p>Termitophily—the symbiosis of organisms with termite societies—has evolved a disproportionate number of times within the rove beetle subfamily Aleocharinae (Staphylinidae). Among aleocharine termitophiles, defensive (limuloid) and mimetic (physogastric & physothoracic) body forms have evolved convergently, but due to lack of a comprehensive aleocharine phylogeny, the context in which termitophily and associated adaptations evolve is unknown. We present the first example of a robust, morphology-based phylogenetic placement of an exclusively termitophilous tribe, the Termitohospitini. Termitohospitini is recovered to be nested within Myllaenini<jats:italic>sensu nov</jats:italic>, and sister to Myllaena (new synonymy). Furthermore, we also recovered the small tribe Masuriini nested within Myllaenini<jats:italic>sensu nov</jats:italic>(new status).</jats:p><jats:p>Reconstructing ecological transitions within this clade, we present evidence that the stem lineage of Myllaenini sensu nov invaded intertidal marine habitats, the common ancestor for Myllaena + Termitohospitini then transitioned to freshwater riparian habitats, with Termitohospitini alone subsequently shifting to termitophily. We conclude that: (1) Termitohospitini was ancestrally a limuloid-bodied riparian inhabitant; (2) a limuloid form may have been pre-adaptive for defense against host attack during the evolution of termitophily; (3) the strongly tapered abdomen of an ancestral limuloid body was a constraint on the evolution of physogastry, leading to the emergence of the unusual physothoracic body form observed in termitohospitines that likely integrates these obligate termitophiles to life inside termite colonies.</jats:p><jats:p>“one of the most astonishing spectacles in all natural history.” — Richard Dawkins</jats:p>