The Tibiotarsal Articulation and Intertibiotarsal Leg Sclerite in Dictyoptera (Insecta)

Abstract

AbstractThe skeletal morphology of the transition area between the tibia and the tarsus is described for Dictyoptera, with a focus on Blaberus craniifer (Blattodea) and Sphodromantis viridis (Mantodea), but with 8 mantodean and 39 blattodean species (including 3 termite species) examined altogether. We emphasise the occurrence in most dictyopterans of a small sclerite located on the anteroventral side of the leg, between the margins of the tibia and the tarsus facing each other, the intertibiotarsal sclerite (abbreviated as itts: tibio-tarsal band/ligament sensu D. Neff and co-workers). The itts region is shown on SEM micrographs for a representative subset of our taxon sample. Comparison with selected outgroup species and data from the literature indicates that sclerite itts is autapomorphic for Dictyoptera and further confirms the monophyly of the group. Details of sclerite itts yield characters for phylogenetic work in Dictyoptera, such as a dorsal extension of the sclerite limited to a subset of our mantodean sample. In Cryptocercidae cockroaches and in termites sclerite itts is vestigial or absent, respectively. This could be interpreted as supporting termites to be the sister group of all remaining Dictyoptera, followed by Cryptocercidae. In the light of recent phylogenetic work, however, this rather appears to be a reductive apomorphy, which then further supports Cryptocercidae to be the sister group of termites. Functional aspects of the tibiotarsal articulation in Dictyoptera are also addressed, with a focus on the roles of and interdependence among the dorsal tibiotarsal articulation, the itts sclerite, and the tendons originating from the proximal rim of the tarsus (bearing the tarsal muscles); on this issue a functional model is presented. Most importantly, the effects of the tarsal muscles are being modulated with the status of itts (expanded or bent underneath).