Transcript quarry

Functional Morphology of the
Middle Ear of Ctenomys talarum
(Rodentia: Octodontidae)
E.C., Schleich, C., Bush (2004) Functional Morphology of the
Middle Ear of Ctenomys talarum (Rodentia:
Octodontidae. J of Mamm, 82: 290-295.
Ctenomys talarum
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Solitary subterranean rodent
Significant features:
-enlarged middle-ear cavity
-round and larger eardrum without pars
flaccida
-no connection between malleus and
tympanic bone
-partial fusion of malleus with incus
-nearly flat stapedial footplate
-Absence of stapedial artery
Continued…
-reduced tensor tympani
-absence of stapedial muscle
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120 and 160 g in body mass for females and
males respectively
Vocalizations are moderate to low in frequency
which common when living in underground
environments.
Observations
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The physical environment exerts strong effects on
design of animal displays, but the influence of
receiver properties on their evolution distinguishes
displays from other traits.
In mammals, hearing properties of the auditory
organ are related strongly to middle-ear
morphology.
According to the optimality principle, physical
characteristics of vocalizations should reflect
adaptation to the physical environment, body size,
or hearing ability.
The Middle Ear
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(1) Malleus ;
(2) Malleus ligament ;
(3) Incus ;
(4) Incus ligament;
(5) Stapes muscle (stapedius);
(6) Stapes footplate;
(7) Eardrum;
(8) Eustachian tube;
(9) Malleus muscle (tensor tympani);
(10) Nerve (chorda tympani) sectioned
Hypothesis
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C. talarum and other
subterranean species
should have anatomical
features that optimize
low-frequency hearing.
Materials and Methods
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Eight adult males and 14 adult females captured
in Mar de Cobo using plastic live traps set at
fresh surface mounds
In lab animals were killed by cervical dislocation
Naso-occipital length and greatest zygomatic
width measured with digital calipers (0.01 mm)
Bullar length, width, and depth measured
With ocular micrometer (0.06 mm) length and
diameter of auditory meatus, diameter of
eardrum, length of head of malleus, length of
lever arm of malleus, length of incus etc.
Results
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Enlarged middle-ear cavity
Round and large eardrum without pars flaccida
Lack of connection between malleus and
tympanic bone
Partial fusion of malleus with incus
Nearly flat stapedial footplate
Reduced (tensor tympani) or absent (stapedial)
middle-ear muscles
Reduced Pinna which accounts for poor soundlocalization capacities of subterranean forms
Comparison Species
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Geomys bursarius- medium to small sized,
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Spalax ehrenbergi - blind mole rat
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Heterocephalus glaber- naked mole-rat
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Clyomys and Octodon
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Cryptomys hottentotus- common mole-rat
dark brown gophers
Comparison
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Reduced size of pinna shared with Spalax
ehrenbergi and Heterocephalus glaber
Round eardrum wit no evident pars flaccida
occurs in C. talarum, S. ehrenbergi, G. bursarius,
and Cryptomys hottentotus
Middle ear cavity of C. talarum enlarged in
comparison with some surface dwellers of
Caviomorpha, although approximating the size
of the middle ear of Geomys bursarius
Walls of middle-ear cavity of C. talarum,
Clyomys, and Octodon are cancellous bone
covered with compact bone
Conclusion
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The middle ear of C. talarum has anatomical
features that are probably adaptations to keep
of enhance low-frequency sounds transductions.
These modifications agree with the dominant
low-frequency vocalizations of C. talarum and
with the best transmission frequency in
subterranean environments.
Modifications also found in several species
of unrelated subterranean rodents.