Better than fish on land? Hearing across metamorphosis in salamanders.
Early tetrapods faced an auditory challenge from the impedance mismatch between air and tissue in the transition from aquatic to terrestrial lifestyles during the Early Carboniferous (350 Ma). Consequently, tetrapods may have been deaf to airborne sounds for up to 100 Myr until tympanic middle ears evolved during the Triassic. The middle ear morphology of recent urodeles is similar to that of early 'lepospondyl' microsaur tetrapods, and experimental studies on their hearing capabilities are therefore useful to understand the evolutionary and functional drivers behind the shift from aquatic to aerial hearing in early tetrapods. Here, we combine imaging techniques with neurophysiological measurements to resolve how the change from aquatic larvae to terrestrial adult affects the ear morphology and sensory capabilities of salamanders. We show that air-induced pressure detection enhances underwater hearing sensitivity of salamanders at frequencies above 120 Hz, and that both terrestrial adults and fully aquatic juvenile salamanders can detect airborne sound. Collectively, these findings suggest that early atympanic tetrapods may have been pre-equipped to aerial hearing and are able to hear airborne sound better than fish on land. When selected for, this rudimentary hearing could have led to the evolution of tympanic middle ears.
['Christensen|Christian Bech|CB|', 'Lauridsen|Henrik|H|', 'Christensen-Dalsgaard|Jakob|J|', 'Pedersen|Michael|M|', 'Madsen|Peter Teglberg|PT|']
D000557:Ambystoma D000818:Animals D004432:Ear, Middle D005072:Evoked Potentials, Auditory D006309:Hearing D007814:Larva D008675:Metamorphosis, Biological
hearing early tetrapods urodeles evolution of aerial hearing vibration detection