An incredibly advanced hearing system which enables a group of insects to listen to the same sound twice with each ear, helping them to locate the sound’s origin with pinpoint accuracy, has been discovered by scientists at the University of Lincoln, UK.
The new Leverhulme-funded research set out to explore how Copiphora gorgonensis – a bush-cricket native to Colombia, South America – is able to hear sound signals from potential mates and to detect the sound source.
Unlike vertebrates, bush-crickets’ ears are located in their forelegs. Each front leg exhibits a single ear below the knee with two eardrums (also known as tympanic membranes), which are backed by a narrow cylindrical tube (the acoustic trachea) running along the leg internally and opening out on the side of the insect’s body.
The researchers found that a single sound actually arrives at the bush-crickets’ ears twice, at different times and with different amplitudes, using the external and internal paths. The eardrums in each leg receive sound from the external side, and internally via the tracheal tube, making this type of ear a ‘pressure difference receiver’. This dramatically improves their ability to locate the sound source.
This significant new discovery helps to explain how these nocturnal insects use their advanced hearing systems to successfully locate their mating partners in the dark.
Dr Fernando Montealegre-Z from the University of Lincoln’s School of Life Sciences led the study. He explained: “Our research used advanced technologies to show how these bush-crickets receive sound signals in a way that enables them to detect their original source. We showed that the sound arrives at each tympanal membrane twice; externally at the normal speed of sound in air and then again internally via the acoustic trachea inside the animal, at a slightly slower speed. Curiously, the sound travelling inside the tracheal tubes is also amplified because the tube has the effect of an acoustic horn, a bit like an ear trumpet. Taken together, this means this tympanal membrane is receiving the signal twice – the first time at normal sound speed and with no amplification, and the second time slower but louder.
The full story is here, and once again, I’m thinking of how often we got such a boring and not so great system.