A cochlear organ for frequency selectivity was thought to be unique to the hearing of mammals until a similar mechanism for frequency analysis was discovered in the ears of bushcrickets in South American rainforests two years ago.
Scientists are under the impression that the discovery of this previously unidentified hearing organ be the beginning of a path leading to technological advancements in bio-inspired acoustic sensors, including hearing aids and medical imaging devices.
The new research project, funded by the Leverhulme Trust, has the aim to develop a deeper understanding of the evolution of ultrasonic hearing in bushcrickets, specifically how they developed the cochlear-like systems in response to changing evolutionary pressures over millions of years.
Project leader Dr Fernando Montealegre-Z, of the School of Life Sciences, University of Lincoln, UK, led the team who discovered the mysterious hearing organ in bushcrickets.
He explained, “We will study these hearing systems and their variation in many species of bushcrickets. There are around 7,000 living species of these insects, but what we know about cochlear mechanisms has been investigated in only two or three. Therefore we expect to find enormous amount of variation across species. Through data from fossils and existing species, we aim to unveil major changes in sensory ecological niches and in the auditory ecology of species which have evolved from a single ancestral species.”
Bushcrickets are among the first terrestrial animals to have evolved acoustic communication. The sound that is emitted from crickets is produced by the stridulatory organ, which is a large vein running along the bottom of one wing covered in “teeth”, which is rubbed against a plectrum on the other wing. The ears, located on the cricket’s forelegs, are used in mating and predator avoidance.
Almost 70 per cent of the living species, measured with ultrasound-sensitive equipment, produce acoustic signals in the ultrasonic range. However, their ancestors communicated at much lower frequencies. Modern bushcrickets emerged about 55-60 million years ago. Since bats emerged at around the same time, the group think that bushcrickets possibly evolved ultrasonic communication and elaborate hearing mechanisms in response to acoustic predators, such as echolocating bats.
For the first time, the group will reconstruct changes in both shape and function of fossil bushcrickets’ auditory and stridulatory organs throughout the recorded history of this group, from the Triassic onwards. This allows them to obtain a greater understanding of the selective pressures that forced the evolution of cochlear systems in mammals and insects.
The work will allow the reconstruction of a series of biophysical models that will stimulate and predict tympanal vibrations and wing resonances in extinct bushcrickets, as well as the acoustic reconstruction of the bushcricket community that lived in the long-gone forests of the Triassic and Jurassic eras.
Dr Montealegre-Z said, “Findings will help to comprehend the multiple origins and diversity of auditory mechanisms in mammals and insects. Results will also open up our understanding of the acoustic ecology of extinct environments where other auditory animals lived, and not only provide insights into the lives of singing insects, but that of their prey and predators. Studying fossil insects advances our general understanding of both behavioral and physical ecologies of the forests of the distant past.
“The research encompasses several disciplines including paleontology, biophysics, physiology and engineering. The integration of these disciplines is original and innovative and will open up new opportunities to enhance the current knowledge of sensory mechanisms in living organisms, including humans.”
Contributing Source: University of Lincoln
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