Feb 12 2020
According to a new study, the ear canals of bush-crickets have evolved to performs functions similar to the ears of mammals to modulate sound pressure and amplify sound. The study outcomes could help researchers develop improved acoustic sensors for human use.
Pictured is a diagram of the bush-cricket Copiphora gorgonensis, which are found in the Colombian rainforest, showing how the sound pressure changes inside its “ear canal.” Image Credit: Dr Thorin Jonsson.
Bush-crickets are insects that survive by relying on acoustic communication. The males sing to attract faraway females. Very small “ears” found in their forelegs function similar to human ears, which have an inner, middle, and outer ear. Several species have transparent “skins,” allowing researchers to measure ear processes.
An international group of mathematicians and sensory biologists discovered that the horn-shaped outer ear of the insects, known as the acoustic trachea tube, traps sound similar to the ear canals of mammals by amplifying and modifying the pressure waves. These waves are subsequently passed to the eardrum surface to enable directional hearing in the insect.
So far, the mechanism that causes such variations in sound pressure levels that has an impact on directional hearing has been obscure. The study outcomes could completely transform the way auditory devices determine the origin or location of a detected sound, thereby helping the design of complex wireless acoustic sensor networks for monitoring and surveillance purposes.
The researchers performed the study on a species known as Copiphora gorgonensis, native to the Colombian rainforest. Three-dimensional X-ray imaging was employed to image the structure of the bush-cricket’s ears. Mathematical analysis was also used to identify how the sound worked within the acoustic tube.
The study was part of a €1.9million European Research Council-funded project headed by Professor Fernando Montealegre-Zapata, an entomologist who specializes in sensory biology and biophysics at the University of Lincoln, United Kingdom. It was performed in collaboration with the University of Bristol, and University of Graz in Austria.
The study was carried out by Dr Emine Celiker, a Research Fellow in numerical modelling in the School of Life Sciences at the University of Lincoln. According to her, “The research is the first step in using combined experimental and mathematical techniques to determine the mechanism crickets use to hear their species’ songs.”
Our findings provide a strong indication that the bush-cricket ear processes sound in the same way a mammal’s does, making its study vital for the development of new auditory sensors. We were able to take recordings of the auditory process using laser doppler vibrometry which measures the vibrations of soundwaves on the surface of the ear canal.
Dr Emine Celiker, Research Fellow in Numerical Modelling, School of Life Sciences, University of Lincoln
Celiker continued, “By applying mathematical modelling of the ears combined with real-life experiments, we also found that the ear canal filters out sound frequencies relevant to the species’ survival, selectively amplifying only frequencies that are behaviourally relevant for the animals—like their mating song or the high-frequency calls of predatory bats.”
Traditionally it is well known that horns increase the volume of sound, and for bush-cricket hearing it has been suspected that this is also the case due to the geometry of its acoustic tube. We verified this after a thorough investigation of the processes involved in the sound amplification. The findings have huge potential to be applied in enhancing acoustic sensors such listening devices.
Dr Emine Celiker, Research Fellow in Numerical Modelling, School of Life Sciences, University of Lincoln
The study outcomes have been reported in Biophysical Journal.