Cockroach homologs of praying mantis peripheral auditory system components

This study identifies the cuticular metatho- racic structures in earless cockroaches that are the ho- mologs to the peripheral auditory components in their sister taxon, praying mantids, and defines the nature of the cuticular transition from earless to eared in the Dic- tyoptera. The single, midline ear of mantids comprises an auditory chamber with complex walls that contain the tympana and chordotonal transduction elements. The cor- responding area in cockroaches, between the furcaster- num and coxae, has many socketed hairs arranged in discrete fields and the Nerve 7 chordotonal organ, the homolog of the mantis tympanal organ. The Nerve 7 chor- dotonal organ attaches at the apex of the lateral ventro- pleurite (LVp), which has the same shape and general structure as an auditory chamber wall. High-speed video shows that when the coxa moves toward the midline, the LVp rotates medially to stimulate socketed hairs, and also moves like a triangular hinge giving the chordotonal or- gan maximal in- out stimulation. Formation of the mantis auditory chamber from the LVp and adjacent structures would involve only enlargement, a shift toward the mid- line, and a mild rotation. Almost all proprioceptive func- tion would be lost, which may constitute the major cost of building and maintaining the mantis ear. Isolation from leg movement dictates the position of the mantis ear in the midline and the rigid frame, formed by the cuticular knobs, which protects the chordotonal organs. J. Morphol. 000:000 - 000, 2005. © 2005 Wiley-Liss, Inc.