Meeting Abstract
P2.146 Monday, Jan. 5 Central nervous system responses to stimulation of the mesothoracic cyclopean ear of the praying mantis, Pseudocreobotra ocellata TORVUND, M.*; YAGER, D.D.; Univ. of Maryland, College Park ddyager@umd.edu
Most praying mantises detect ultrasound using a single ear in the ventral midline of the metathorax. This provides early warning of a bat attack and triggers an effective evasive response. A few mantis lineages have evolved a second, serially homologous, mesothoracic auditory system tuned to 2-4 kHz sounds. Based on extracellular recordings using 2.5 kHz stimuli at 15-25 dB over threshold, information from the mesothoracic ear ascends via at least two interneurons with high conduction velocities and arrives in the cephalic ganglia 17-24 ms after stimulus onset. A rapid pathway is indicated by activity in three or more interneurons descending from the cephalic ganglia only 25-30 ms after the stimulus, which suggests minimal intermediate processing. These descending responses habituate strongly. A slower pathway is indicated by a weakly habituating descending interneuron with very large spikes in the extracellular record and latencies of 50-70 ms. The tuning curves for the descending units are identical in shape to the ascending units’ curves, but the thresholds are 15-20 dB higher (means of 68 dB SPL vs. 50 dB SPL at 2.5 kHz). In addition, at least three axons descend from the mesothorax into the abdomen. Average latencies at 15-25 dB over threshold recorded between the 2nd and 3rd abdominal ganglia ranged from 14-20 ms. There was no indication of long-latency activity descending from the head into the abdomen. Thus, information about 2-4 kHz sounds is widely and very rapidly distributed throughout the CNS and a separate slower processing pathway probably exists as well. This is a pattern commonly seen in arthropod escape systems where behavioral latencies are typically 40-80 ms. Nonetheless, attempts to elicit behavioral responses to diverse 2-4 kHz stimuli in a broad range of contexts were not successful. The behavioral role of mantis mesothoracic hearing remains unknown.
