Picometre scale mechanics in the cicada ear

Female cicadas use sound to select their mate from a chorus of singing males. Cicadas have tympanal ears, with both the ear's tympanal membrane, and constituent tympanal ridge, acting as acousto-mechanical transducers and frequency filters. Within the ear the tympanal ridge is mechanically connected to a large number of mechanosensory neurons via a cuticular extension known as the tympanal apodeme. Using microscanning laser Doppler vibrometry, the in vivo vibrations of the tympanal apodeme of female Cicadatra atra have been measured for the first time as they respond to the motion of the tympanal membrane driven by sound. These precise measurements reveal that the tympanal membrane's nanometre motion is over a magnitude greater than that of the tympanal apodeme at the point where the neurons attach. Further, the tympanal apodeme acts as an additional mechanical frequency filter, enhancing the frequency filtering of the tympanal ridge, to narrow the frequency band of vibration at the mechanoreceptor neurons solely to that of the male calling song. This study thus enhances our understanding of the mechanical links between the external ear of the cicada and its sensory cells. Poster Session held on Tuesday 30th June 2009 at the Annual Meeting of the Society for Experimental Biology, 28th June-1st July, Glasgow, UK.