Auditory fovea in the ear of a duetting katydid shows male-specific adaptation to the female call.

Convergent evolution has led to surprising functional and mechanistic similarities between the vertebrate cochlea and some katydid ears [1,2]. Here we report on an 'auditory fovea' (Figure 1A) in the duetting katydid Ancylecha fenestrata (Tettigoniidae). The auditory fovea is a specialized inner-ear region with a disproportionate number of receptor cells tuned to a narrow frequency range, and has been described in the cochlea of some vertebrates, such as bats and mole rats [3,4]. In tonotopically organized ears, the location in the hearing organ of the optimal neuronal response to a tone changes gradually with the frequency of the stimulation tone. However, in the ears of A. fenestrata, the sensory cells in the auditory fovea are tuned to the dominant frequency of the female call; this area of the hearing organ is extensively expanded in males to provide an overrepresentation of this behaviorally important auditory input. Vertebrates developed an auditory fovea for improved prey or predator detection. In A. fenestrata, however, the foveal region facilitates acoustic pair finding, and the sexual dimorphism of sound-producing and hearing organs reflects the asymmetry in the mutual communication system between the sexes (Figures 1B, S1).