A grant of £250,000 from The Leverhulme Trust has been awarded to a team of scientists led by the University of Lincoln, UK, to study how a group of insects evolved incredible ultrasonic hearing abilities.
A cochlear organ for frequency selectivity was thought to be unique to hearing in mammals until a similar mechanism for frequency analysis was found in the ears of bushcrickets in South American rainforests two years ago.
Scientists believe the discovery of this previously unidentified hearing organ could pave the way for technological advancements in bio-inspired acoustic sensors, including medical imaging devices and hearing aids.
The new research project, funded by The Leverhulme Trust, aims to develop an integrated understanding of the evolution of ultrasonic hearing in bushcrickets; specifically how they developed cochlear-like systems in response to changing evolutionary pressures over millions of years.
Project lead Dr Fernando Montealegre-Z, from the School of Life Sciences, University of Lincoln, UK, led the team who discovered the previously unidentified 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 emitted by crickets is produced by the stridulatory organ, a large vein running along the bottom of one wing, covered with “teeth”, which is rubbed against a plectrum on the other wing. The ears, located on their forelegs, are used in mating and predator avoidance.
Nearly 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 some 55-60 million years ago. Since bats arose at about the same time, the group hypothesise that bushcrickets might have evolved ultrasonic communication and elaborate hearing organs in response to acoustic predators, such as echolocating bats.
For the first time, the group will reconstruct changes in shape and function of fossil bushcrickets’ auditory and stridulatory organs throughout the recorded history of this group, from the Triassic onwards. This will enable them to understand the selective pressures that drove the evolution of cochlear systems in mammals and insects.
The work will enable the construction of a series of biophysical models that will simulate and predict tympanal vibrations and wing resonances in extinct bushcrickets, plus 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 behavioural 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.”