Genital morphology and mating behaviour of Allostethus (Dermaptera), an earwig genus of enigmatic phylogenetic position

In the suborder Forficulina (order Dermaptera; earwigs), the families Apachyidae, Anisolabididae, and Labiduridae form a possibly paraphyletic assemblage Mesodermaptera, which is characterized by laterally paired penes that point in opposite directions (anterior and posterior) when in repose. A previous study of a labidurid species, Labidura riparia (Pallas, 1773), revealed that males predominantly use the right penis for insemination, although both penes are functional. This result suggests that labidurids may have retained handedness in penis use, leading eventually to the loss of the less frequently used left penis in the common ancestor of the Eudermaptera, estimated to be the sister clade of Labiduridae. However, Haas & Kukalovà-Peck (2001: European Journal of Entomology 98: 445 - 509) included another representative of Labiduridae, Allostethus indicum (Burmeister, 1838) (Allostethinae) in their extensive phylogenetic analysis, and found that hindwing structures of this species showed multiple plesiomorphic characteristics, making Labiduridae (sensu lato) a polyphyletic assemblage. The aim of the present study was to describe the genital structures and copulation of A. indicum in detail. The genital morphologies of a congener and other labidurid genera (Nala, Labidura, Forcipula) were also examined for comparison. Male A. indicum predominantly used (or were ready to use) the right penis for insemination, as in L. riparia. However, the possible female genital structure responsible for this handedness differed between the two species: the base of the spermatheca showed a striking spiral in L. riparia, while the spermatheca opened to an asymmetrically arranged vagina in Allostethus. Female Allostethus also possessed a pair of elongated thin tubes, which have to date been reported only for the basal groups of earwigs, as well as the vagina and the internally branched spermatheca. The developmental origin of an ovipositor-like sutucture also differs between Allostethus and the other labidurids examined, lending support to the polyphyly of Labiduridae sensu lato.