| Abstract #375, Date 2/15/99, Session K6, Poster (B122) |
| DPOAE from the cochlea of the tenrec, Echinops telfairii |
| *B.M. Faulstich (Zoologisches Institut der LMU); S. Radtke-Schuller (Anatomische Anstalt der LMU); M. Koessl (Zoologisches Institut der LMU) |
The Madagascar tenrec, Echinops telfairii, is an insectivore with little differentiation from the ancestral form. It has a hearing range from about 5 to 50 kHz and has been suspected to use echolocation for orientation in its environment. To gain insight into the variation of function and the correlated evolutionary development of the cochlea in mammals, cochlear function in the tenrec has been assessed using distortion product otoacoustic emissions (DPOAE). A distortion threshold curve, iso-suppression tuning curves (STC) of the 2f1-f2 DPOAE and the optimum primary ratio (f2/f1) were determined. Additionally, the group delay of the 2f1-f2 DPOAE, reflecting the time constants involved in the generation and transmission of DPOAE, was calculated. The distortion threshold curve showed a broad minimum between 10 and 35 kHz and steep flanks. While the low frequency flank was very constant over time and between individuals, the high frequency flank showed greater variation. This may be due to influences of the animal's hibernation pattern. STCs displayed the typical mammalian shape and reflected low to moderate tuning sharpness. Similar to an observation in the opossum, Monodelphis domestica, the shape of STCs for high f2 frequencies may reflect the limit of cochlear frequency representation around 35 kHz. The group delay of the 2f1-f2 DPOAE showed a continous decrease with increasing primary frequency and lay in the range from 0.17 to 2.23 ms. This is comparable to the situation in the Mongolian gerbil. The findings indicate that cochlear function in the Tenrec appears to be similar to that found in presumably more modern mammals with neither primitive features nor specializations. |