Ninety million years of chasing mites by ant-like stone beetles

Abstract

Among insects, the largest group of the Animal Kingdom, rove beetles (Staphylinidae) have undergone an enormous adaptive radiation that resulted in over 62,000 extant species showing diverse body forms, structures and feeding specializations combining predaceous, mycophagous, saprophagous and phytophagous habits in one family. The morphology of extinct and extant species is well studied, but the evolutionary history of such a broad range of adaptations is scarcely documented in the fossil record, and therefore poorly understood. One of the most puzzling specializations is that of predaceous ant-like stone beetles (Scydmaeninae), a staphylinid subfamily whose members choose not a soft-bodied prey, but the most heavily sclerotized, well-protected armoured mites. Scydmaenines have evolved a unique prey capturing apparatus with adhesive suckers to capture their prey, and the feeding process is remarkably long, often exceeding 30h. The mouthparts with paired suckers cannot be used to catch any other kind of prey, and therefore finding such a device in extinct taxa implies specialized acarophagy. For the first time, we demonstrate that this very narrow specialization has ancient origins, and the Mesozoic (Turonian) Hyperstenichnus vendeanus Jałoszyński & Perrichot, gen. et sp. nov. from Vendean (French) amber was already an advanced, specialized mite killer. Surprisingly, the mouthpart modifications of the new species are more advanced than those in its extant relatives, suggesting that its (possibly too) narrowly specialized lineage has gone extinct. A long stasis of morphological structures is well known among Staphylinidae, and now also antiquity of narrow feeding specializations in rove beetles can be postulated, with unique habits remaining unchanged for over 90millionyears.