An Eocene insect could hear conspecific ultrasounds and bat echolocation

Area of Science:

• Evolutionary biology
• Bioacoustics
• Paleontology

Background:

• Hearing has evolved independently multiple times, with insect ears like those of katydids (Orthoptera: Tettigoniidae) playing key roles in communication and predator detection.
• Katydid ears possess unique outer, middle, and inner ear components analogous to mammalian ears, featuring tympana in the forelegs that receive sound via pinnae and an ear canal (EC).
• While the biophysics and function of katydid ears are increasingly understood, their evolutionary origins remain unclear.

Purpose of the Study:

• To investigate the evolutionary history and emergence of the unique katydid ear structure.
• To determine the acoustic communication frequencies and hearing capabilities of an ancient katydid species.

Main Methods:

• Microcomputed tomography (μCT) scanning was used to reconstruct the outer ear and wing geometries of a well-preserved katydid fossil from Baltic amber (approx. 44 million years old).
• Numerical and theoretical modeling of the fossilized wings was employed to analyze acoustic properties.
• Biophysical modeling of the ear's geometry was performed to assess its tuning and sensitivity.

Main Results:

• The study identified a peak communication frequency of 31.62 (± 2.27) kHz for the fossilized katydid species.
• The reconstructed ear was found to be biophysically tuned to this communication frequency and capable of detecting higher-frequency ultrasounds (>80 kHz).
• These findings suggest the katydid ear's advanced features, including broadband ultrasonic sensitivity, were present in the Eocene.

Conclusions:

• The unique, complex ear structure of katydids, with biophysical properties analogous to mammalian ears, emerged during the Eocene epoch.
• The fossil evidence demonstrates that these insects possessed sophisticated hearing capabilities for both communication and predator detection millions of years ago.
• This study provides crucial insights into the early evolution of auditory systems in insects and their ecological roles.