Hynek Burda (2006): Ear and eye in subterranean mole-rats, Fukomys
anselli (Bathyergidae) and Spalax ehrenbergi (Spalacidae): progressive
specialisation or regressive degeneration? Animal Biology, 56(4),
475-486
Abstract: The hearing and visual ecology of mole-rats, Spalax
ehrenbergi (Spalacidae) from Israel and Fukomys (formerly Cryptomys)
anselli (Bathyergidae) from Zambia, two rodent taxa that have
independently adapted to subterranean life, are reviewed and compared
with epigeic counterparts, the laboratory rat and the guinea pig. In
burrows, airborne sounds of low frequencies (200-800 Hz) are least
attenuated and even accentuated over short distances. In both mole-rat
species the frequency range of the best hearing is shifted to match
the frequencies best propagated in tunnels: hearing sensitivity in the
lower frequency range (<16 kHz) has been conserved or further
improved. Compared to the rat, the hearing range (covering about eight
octaves) in mole-rats is not restricted but only shifted towards lower
frequencies.
Morphologies of the middle and inner ears of mole-rats and the guinea
pig are similar in some aspects and suggest tuning to low
frequencies. The middle ear morphology of mole-rats does not seem to
explain the lower high-frequency limit of hearing. Middle ear is not
reduced or degenerated. On the contrary, the incus and the stapedial
footplate are markedly enlarged, resulting in reduced
sensitivity. These features can be considered an adaptation to
compensate for local sound amplification in burrows. The cochlea and
its components are highly specialised for sensitive perception and
high resolution of low frequencies.
Despite living in the same optic environment, Spalax and Fukomys show
different degrees of regression and specialisation of the visual
system. The eye in Spalax is severely regressed and shortwave-opsin
cones are missing. Spalax is blind but the retina has retained its
role for photoperiodic perception. Fukomys has small, yet
morphologically normal, eyes, with a retina rich in 'blue' cones. It
has retained basic visual capabilities; however, the role of light as
a zeitgeber is not conclusive.
Key words: convergence; Cryptomys anselli; ear; eye; Fukomys anselli;
hearing; Spalax ehrenbergi; subterranean rodent; vision.
DOI: 10.1163/157075606778967847
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University of Vienna, Dept. of Behavioral Biology
Sonja Amoser
PhD Student, Research Associate
Althanstrasse 14
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