Better Never than Late? Convergent Loss of Late-Forming Ears in Toads

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Journal/Book Title/Conference

Society for Integrative and Comparative Biology Meeting


Portland, OR

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Anurans have outer and middle ear structures to transmit airborne sound from the environment to their inner ear sensory cells. Yet, many bufonid (true toad) species have independently evolved earlessness, the lack of middle and outer ear structures, despite the importance of acoustic communication in most toad mating systems. Our work aims to determine why middle and outer ear structures are so evolutionarily labile in the Bufonidae family by comparing hearing and morphological data of eared and earless bufonid species within a phylogenetic context. We show that the middle and outer ear structures form very late in the development of toads and take many months past metamorphosis to become fully functional. Adult earless species are typically less sensitive to acoustic stimuli at high frequencies and more sensitive to low frequency vibrations compared to eared toads. The skulls of earless species neither lack other skull bones nor are less ossified than skulls of eared species. We conclude that extratympanic hearing pathways buffer the hearing consequences of tympanic ear loss, and we discuss roles for heterochrony and directional selection in shaping the evolutionary lability of ear structures.

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