A new study on an extinct katydid preserved in amber has shed light on the ancient acoustic communication of insects and their predators.
The research, published in the journal Palaeontology, revealed that katydids have been using ultrasounds for millions of years to avoid being detected by bats and other eavesdroppers.
The Sound of Silence
LILLIAN SUWANRUMPHA/AFP via Getty Images
The fossil insect, named Archaboilus musicus, belongs to the family Tettigoniidae, also known as katydids or bush crickets. It was found in a piece of Burmese amber that dates back to the mid-Cretaceous period, about 100 million years ago.
The amber also contains a feather, suggesting that the insect lived in a forest environment.
The researchers, led by Dr. Fernando Montealegre-Zapata from the University of Lincoln, UK, used micro-CT scanning and 3D reconstruction to examine the morphology and anatomy of the fossil.
They found that the insect had a complex stridulatory apparatus, consisting of a file and a scraper on its forewings, that enabled it to produce sounds by rubbing them together.
The researchers also reconstructed the acoustic signal of the insect by measuring the dimensions and spacing of the teeth on the file.
They found that the insect produced a pure-tone song with a frequency of about 6.4 kHz, which is within the range of human hearing.
However, the song also had a strong ultrasonic component, with harmonics reaching up to 50 kHz, which is beyond the hearing range of most mammals, but within the echolocation range of bats.
The researchers suggested that the insect used its ultrasonic song as a form of acoustic camouflage, to avoid being detected by bats and other predators that use sound to locate their prey.
They also proposed that the insect used its pure-tone song as a mating signal, to attract females of the same species.
The study provides the first direct evidence of ultrasound production in fossil insects, and showed that katydids have been using this strategy for a long time in their evolutionary history.
The researchers also compared the fossil insect with its living relatives, and found that it belongs to an ancient lineage that diverged from the modern katydids about 200 million years ago.
The researchers argued that the evolution of ultrasound production in katydids was driven by the coevolutionary arms race between insects and bats, which emerged in the late Jurassic period, about 160 million years ago.
Bats are known to be the main predators of katydids, and they use echolocation to hunt them in the dark. Katydids, in turn, have developed various adaptations to evade bat predation, such as ultrasound detection, evasive flight, and acoustic camouflage.
The researchers concluded that the fossil insect in amber reveals the evolutionary battles of ancient Europe, when insects and bats were engaged in a sonic warfare that shaped their diversity and survival.
They also suggested that the fossil insect represents a new genus and species of katydid, and name it Archaboilus musicus, meaning "ancient beautiful singer".
