DEVELOPMENT OF HEARING AND VOCALIZATION IN A MARSUPIAL, THE NORTHERN QUOLL, DASYURUS-HALLUCATUS

The development of hearing was studied in the Northern Quoll, a noctur nal marsupial carnivore whose young are born into a pouch in an immatu re state after about 21 days in utero. Startle responses to noise burs ts of 105 dB sound pressure level first appeared at 60 days after arri val in the pouch, but only to occasional stimuli; forelimb rather than whole body twitches were evoked. The latter were elicited regularly a t 67 days onward. Auditory brainstem response (ABR) audiograms were me asured during the period when startle responses first appeared. At 68 days responses were elicited between 1 and 16 kHz with thresholds in e xcess of 55 dB. At 81-88 days responses occurred over the adult range at lower thresholds than observed in the adult. The waveform of the AB R increased in complexity and decreased in latency during development. Pouch-young emitted acoustically well-defined isolation calls when se parated from their mothers. Fourier analysis of these calls revealed p eak energy at 8-11 kHz irrespective of the sex of the pouch-young. The isolation call first became evident at about 35 days, when the young were deliberately removed from the nipple, and ceased being emitted be yond about 80 days, some 5 or so days after the eyes open, when the yo ung leave the pouch for substantial amounts of time. The spectrum of t he call was similar at all ages within this 45 day period, and its pea k frequency correlated closely with the best frequency in the adult qu oll's ABR audiogram. At approximately 80 days of age the calls develop ed major low frequency components, similar to those measured in adult vocalizations, and the contributions of frequencies between 8-11 kHz w aned in importance.The results indicate that the onset of hearing in q uells occurs at a relatively early time in the course of their develop ment, but prior to this time the pouch-young emit characteristic isola tion calls easily detectable by the mother. (C) 1996 Wiley-Liss, Inc.