Abstract 55, Date 1:00 pm, Tuesday, February 19, 2008 (48 hours) Session O2: Poster
Mostly Malleus: Low-Frequency Specialization in the Golden Mole Middle Ear
*Peter Narins, Urban Willi
Golden moles, found exclusively in sub-Saharan Africa, are nocturnal, surface-foraging omnivores with rudimentary vision. Several species possess massively hypertrophied mallei that presumably confer low-frequency, substrate-vibration sensitivity through inertial bone conduction. When foraging, the Namib Desert golden mole, Eremitalpa granti namibensis moves between sand mounds containing most of the living biomass in the Namib Desert. Foraging trails are punctuated with characteristic sand disturbances called ìhead dips”, discrete locations where the animal is thought to obtain a seismic ìfix” on the next mound to be visited. Geophone recordings from the mounds reveal spectral peaks centered at ca. 300 Hz, ca. 15 dB greater in amplitude than those from the flats. Moreover, the mallei of the golden moles in the genera Chrysochloris and Eremitalpa are massively hypertrophied. In fact, out of the 117 species for which data are available, these golden moles are among those with the greatest ossicular mass relative to body size. Laser Doppler vibrometric measurements of the malleus head in response to seismic stimuli in Chrysochloris reveals peak sensitivity to frequencies below 300 Hz. Moreover, the orientation of the rotatory axis of the malleus is frequency-dependent. Functionally, these animals appear to be low-frequency specialists, and it is likely that golden moles hear through substrate conduction. Supported by NIH grant DC00222 to PMN.&[nl]&[nl]