P2.133 Thursday, Jan. 5 Comparative study of large axons in the abdominal connectives of mantids (Mantodea) and cockroaches (Blattodea) TRIBLEHORN, Jeffrey D*; PAOLINI, Marissa L; YAGER, David D; FREDERICK-HUDSON, Katy H; College of Charleston; College of Charleston; University of Maryland, College Park; University of Missouri, Columbia firstname.lastname@example.org
Insect nervous systems lack myelinated axons and must increase axon diameter for faster action potential propagation. In abdominal connectives, large diameter axons are typically associated with the wind-sensitive cercal system that mediates escape and flight behaviors. These large axons carry information from the rear of the animal to the thoracic motor centers. Since not all insects fly or exhibit escape responses, large diameter axons likely vary based on these behaviors across species. We compared: 1) the nine largest axons in the abdominal connectives in five cockroach species and twenty mantis species; 2) the four largest axons in the dorsal and ventral intermediate tracts (DIT and VIT) due to their behavioral relevance: the VIT initiates escape responses while the DIT mediates continued escape running and flight maintenance and 3) morphological characters related to the cercal system. Initial results suggest cockroaches that exhibit escape responses possess similar, potentially adaptive, characteristics that are not present in non-escaping cockroach species. In mantids, sexual dimorphism in flight is reflected in the DIT. In Parasphendale affinis, DIT neurons occupy more connective space in flying males than in non-flying females, but the DIT dimorphism does not exist in Hierodula grandis where both sexes fly. Our data set includes several morphological and neural characteristics that can be mapped onto existing cockroach and mantis phylogenies to trace the evolutionary development of large diameter axons in these groups. Funding: NIH National Center for Research Resources Grant P20 RR-016461 and HHMI.