title: Better than fish on land? Hearing across metamorphosis in salamanders.
abstract: 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.
authors: Zoophysiology, Department of Bioscience, Aarhus University, Building 1131, C. F. Moellers Allé 3, Aarhus C 8000, Denmark christian.bech@biology.au.dk.
authors: Christian Bech
authors: CB
authors: Christensen
authors: Comparative Medicine Lab, Aarhus University Hospital Skejby, Aarhus N 8200, Denmark.
authors: Henrik
authors: H
authors: Lauridsen
authors: Department of Biology, University of Southern Denmark, Campusvej 55, Odense M 5230, Denmark.
authors: Jakob
authors: J
authors: Christensen-Dalsgaard
authors: Comparative Medicine Lab, Aarhus University Hospital Skejby, Aarhus N 8200, Denmark.
authors: Michael
authors: M
authors: Pedersen
authors: Zoophysiology, Department of Bioscience, Aarhus University, Building 1131, C. F. Moellers Allé 3, Aarhus C 8000, Denmark.
authors: Peter Teglberg
authors: PT
authors: Madsen
mesh_terms: D000557:Ambystoma / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology*; D000818:Animals; D004432:Ear, Middle / Q000033:anatomy & histology / Q000502:physiology; D005072:Evoked Potentials, Auditory; D006309:Hearing / Q000502:physiology; D007814:Larva / Q000033:anatomy & histology / Q000502:physiology; D008675:Metamorphosis, Biological
keywords: early tetrapods; evolution of aerial hearing; hearing; urodeles; vibration detection
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