Development of hearing in the big brown bat
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ORIGINAL PAPER
Development of hearing in the big brown bat Doreen Möckel1 · Thomas Groulx1 · Paul A. Faure1 Received: 9 July 2020 / Revised: 24 September 2020 / Accepted: 23 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract We studied the development of hearing in newborn pups of the big brown bat, Eptesicus fuscus. In the majority of pups, the opening of both outer auditory canals occurred on or before postnatal day (PND) 7, but in some, it extended to PND 11. Using repeated auditory brainstem response (ABR) recordings, we tracked the progressive development and maturation of auditory sensitivity in 22 E. fuscus pups every 3 days, from PND 10 to PND 31, with additional recordings in a subset of bats at 2 months, 3 months and 1 year of life. There was a profound increase in auditory sensitivity across development for frequencies between 4 and 100 kHz, with the largest threshold shifts occurring early in development between PND 10 and 19. Prior to PND 13–16 and when pups were still non-volant, most bats were unable to hear frequencies above 48 kHz; however, sensitivity to these higher ultrasonic frequencies increased with age. Notably, this change occurred near the age when young bats started learning how to fly and echolocate. Keywords Audiogram · Auditory brainstem response · Eptesicus fuscus · External ear canal · Pup auditory maturation Abbreviations ABR Auditory brainstem response PND Postnatal day
Introduction Bats (Order Chiroptera) are the second largest and only group of mammals to have evolved powered flight. All bats are nocturnal and most echolocate. Bats have exceptional hearing which they use for passive orientation, alerting functions, and social communication. Echolocating bats also use their hearing for active orientation and foraging (Fenton et al. 2016). Hearing by bats has typically been studied with behavioral testing procedures or more invasive physiological methods and terminal procedures. A relatively non-invasive tool to examine hearing in human and non-human animals is the auditory brainstem response (ABR). By placing contact or subdermal electrodes near the auditory bullae at the base of the head and repeatedly presenting sounds and averaging the recorded signal, * Paul A. Faure [email protected] 1
Department of Psychology, Neuroscience & Behaviour, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4K1, Canada
the ABR emerges as a time-locked signal (Shaw 1988). A typical ABR waveform consists of several peaks (I–V) that are understood to represent the synchronous and summed responses of ascending auditory neurons between the cochlea and upper brainstem (Melcher and Kiang 1996). Several studies have used ABRs to measure hearing in adult bats, including Myotis lucifugus (Grinnell 1963), Plecotus townsendii (Grinnell 1963), Rousettus aegyptiacus (Belknap and Suthers 1982), Noctilio leporinus (Wenstrup 1984), Eptesicus fuscus (Simmons et al. 1990; Burkard and Moss 1994), Lasiurus borealis (Obrist and Wenstrup 1998), Pipistrellus abramus
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