Meeting Abstract

P2.60  Friday, Jan. 4  Why is the cyclopean ear of the praying mantis in a midline chamber? YAGER, D.D.**; SCHLUMPF, C.; KOYUNCU, I.H.; Univ. of Maryland, College Park; Univ. of Maryland, College Park; Univ. of Maryland, College Park ddyager@umd.edu

Most praying mantids have a single ear in the ventral midline of the metathorax between the coxae. A deep, partially closed auditory chamber contains two tympana facing each other. In Hierodula grandis, methacrylate casts reveal an irregularly shaped chamber 1.9 mm long with a volume of 1.1 microliters. Neurophysiological audiograms show best frequencies of 30-35 kHz with a secondary sensitivity peak at 60-80 kHz. To determine the contribution of the chamber to mantis hearing, we determined sensitivity and tuning before and after opening the chamber. Other experiments controlled for the cutting of one tympanal nerve that necessarily accompanied the ablation. We also compared the effects of filling the chamber with helium and with nitrogen. The ablation studies showed that the chamber contributes 2-10 dB of sensitivity to the auditory system. The increase sensitivity was maximal at 60-70 kHz, intermediate at 20-30 kHz and minimal at 40-50 kHz. Helium in the chamber caused no change around the best frequency. However, sensitivity decreased as stimulus frequency increased above 50 kHz, which could indicate a selective sensitivity peak shift to > 100 kHz. Evolutionarily and ontogenetically the mantis ear derives from structures lateral to the midline. The reason for the transposition of the precursors to a midline chamber became obvious through high-speed video micrography. Coxal movement massively deforms the cuticle lateral to the midline. Minimal deformation occurs in the midline, however, providing a relatively immobile site for the tympana. The ear is further stabilized by thickened cuticle, especially at the rostral end of the chamber. Thus, the midline auditory chamber provides both acoustic and protective mechanical benefits.