Abstract
Little is known about the ontogeny of lingual echolocation. We examined the echolocation development of Rousettus aegyptiacus, the Egyptian fruit bat, which uses rapid tongue movements to produce hyper-short clicks and steer the beam's direction. We recorded from day 0 to day 35 postbirth and assessed hearing and beam-steering abilities. On day 0, R. aegyptiacus pups emit isolation calls and hyper-short clicks in response to acoustic stimuli, demonstrating hearing. Auditory brainstem response recordings show that pups are sensitive to pure tones of the main hearing range of adult Rousettus and to brief clicks. Newborn pups produced clicks in the adult paired pattern and were able to use their tongues to steer the sonar beam. As they aged, pups produced click pairs faster, converging with adult intervals by age of first flights (7–8 weeks). In contrast with laryngeal bats, Rousettus echolocation frequency and duration are stable through to day 35, but shift by the time pups begin to fly, possibly owing to tongue-diet maturation effects. Furthermore, frequency and duration shift in the opposite direction of mammalian laryngeal vocalizations. Rousettus lingual echolocation thus appears to be a highly functional sensory system from birth and follows a different ontogeny from that of laryngeal bats.
Highlights
Bat echolocation is highly adaptive, requiring extensive motor control to dynamically adjust spectrotemporal properties and beam shape to navigate sensorybehavioural challenges [1,2,3,4,5,6]
We examined the ontogeny of echolocation clicks in the Egyptian fruit bat, Rousettus aegyptiacus
We assessed the ontogeny of lingual echolocation in Egyptian fruit bats by analysing click frequency, duration and temporal emission patterns recorded from pups once a week from day 0 to day 35 postbirth
Summary
Bat echolocation is highly adaptive, requiring extensive motor control to dynamically adjust spectrotemporal properties and beam shape to navigate sensorybehavioural challenges [1,2,3,4,5,6]. Rousettus aegyptiacus adults produce clicks in pairs, rapidly shifting the beam direction of each click within the pair without head movements This beam steering is achieved by very rapid tongue movements which drive the beam direction in a left– right–right–left alternating pattern. In this specialized strategy, Egyptian fruit bats accurately point the maximum derivative of their beam towards objects of interest to improve its localization [28,36,37]. We assessed the ontogeny of lingual echolocation in Egyptian fruit bats by analysing click frequency, duration and temporal emission patterns recorded from pups once a week from day 0 to day 35 postbirth. We expected that beam-steering abilities require experience to perform and will not be present in young pups
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