379
ing of modifi ed orientation patterns, of different arrangements of maculae in 2D and
3D and of changed otolith morphology. Methodological innovations are especially
important to improve auditory measurements to better disentangle the proportion of
particle motion and pressure information detected by the fi sh at certain frequencies
(Popper and Fay 2011 ; Ladich and Fay 2013 ). Despite the application of particle
motion sensors or a set of hydrophones to evaluate particle motion of the sound fi eld
“during” measurements (for an overview see Fay 1988 ; Ladich and Fay 2013 ), a
simple way for directly measuring particle motion and/or pressure detection in
fi shes is still lacking and is the main reason why clear evidence for the detection of
both acoustical components is restricted to just a few species (e.g., Gadus morhua ,
see Hawkins 1993 and Carribean Stegastes species, Pomacentridae, Myrberg and
Spires 1980 ).
Another aspect of inner ear diversity that is related to sensory epithelia is the
morphology of the apical surface of the supporting cells and ciliary bundle morphology, i.e. bundle length and width as well as the ratio of kinocilium length to the
longest stereovillus. Especially deep-sea fi shes display a great variability of ciliary
bundle morphology and supporting cells, with several species possessing exceptionally long ciliary bundles on certain portions of the maculae and/or special regions of
supporting cells interspersed into the macula or adjacent to dorsal or ventral macula
portions (see Table 2 and Fig. 5c ) (Popper 1980 ; Deng et al. 2011 , 2013 ). Soundexposure experiments on goldfi sh are suggestive of long bundles (formerly classifi ed as F3-type, see Popper and Platt 1983 ) primarily detecting low frequencies (100
Hz), whereas shorter bundles (formerly classifi ed as F1-type, see Popper and Platt
1983 ) in the anterior and middle portion of the macula seem to be sensitive to higher
frequencies (≥800 Hz) (Smith et al. 2011 ). Based on these studies it was assumed
that deep-sea fi shes are particularly sensitive to low frequencies or that long ciliary
bundles also represent an adaptation to high water pressures (e.g., Deng et al. 2011 ).
Studies in tetrapods on the relationship between ciliary bundle length and frequency
(e.g., Manley 2000 ; Arch et al. 2012 ) are in accordance with those in fi shes, i.e.
shorter bundles are more sensitive to higher frequencies. However, further studies
similar to the experiments with goldfi sh (Smith et al. 2011 ) are needed for other fi sh
species that lack ancillary auditory structures or any gas-fi lled bladders. Modeling
of the micromechanical behavior of different ciliary bundle types from the macula
utriculi of a red-eared turtle ( Trachemys ( Pseudemys ) scripta ) indicates that the
length ratio of the kinocilium (K) compared to the tallest stereovillus (S) infl uences
bundle stiffness and the magnitude of tensions of the tip links (=links connecting the
tips of stereovilli to each other) (Silber et al. 2004 ). Bundles in which the kinocilium
is only slightly longer than the tallest stereovillus are stiffer and tensions of tip links
are lower when the same force of defl ection is exerted than in bundles with a distinctly longer kinocilium compared to the tallest stereovillus. Ciliary bundles with a
large KS ratio were assumed to possess a wider operational range with respect to
bundle displacement but that they have lower sensitivities to bundle displacement
(Baird 1994 ).
Diversity of Inner Ears in Fishes: Possible Contribution Towards Hearing…
ing of modifi ed orientation patterns, of different arrangements of maculae in 2D and
3D and of changed otolith morphology. Methodological innovations are especially
important to improve auditory measurements to better disentangle the proportion of
particle motion and pressure information detected by the fi sh at certain frequencies
(Popper and Fay 2011 ; Ladich and Fay 2013 ). Despite the application of particle
motion sensors or a set of hydrophones to evaluate particle motion of the sound fi eld
“during” measurements (for an overview see Fay 1988 ; Ladich and Fay 2013 ), a
simple way for directly measuring particle motion and/or pressure detection in
fi shes is still lacking and is the main reason why clear evidence for the detection of
both acoustical components is restricted to just a few species (e.g., Gadus morhua ,
see Hawkins 1993 and Carribean Stegastes species, Pomacentridae, Myrberg and
Spires 1980 ).
Another aspect of inner ear diversity that is related to sensory epithelia is the
morphology of the apical surface of the supporting cells and ciliary bundle morphology, i.e. bundle length and width as well as the ratio of kinocilium length to the
longest stereovillus. Especially deep-sea fi shes display a great variability of ciliary
bundle morphology and supporting cells, with several species possessing exceptionally long ciliary bundles on certain portions of the maculae and/or special regions of
supporting cells interspersed into the macula or adjacent to dorsal or ventral macula
portions (see Table 2 and Fig. 5c ) (Popper 1980 ; Deng et al. 2011 , 2013 ). Soundexposure experiments on goldfi sh are suggestive of long bundles (formerly classifi ed as F3-type, see Popper and Platt 1983 ) primarily detecting low frequencies (100
Hz), whereas shorter bundles (formerly classifi ed as F1-type, see Popper and Platt
1983 ) in the anterior and middle portion of the macula seem to be sensitive to higher
frequencies (≥800 Hz) (Smith et al. 2011 ). Based on these studies it was assumed
that deep-sea fi shes are particularly sensitive to low frequencies or that long ciliary
bundles also represent an adaptation to high water pressures (e.g., Deng et al. 2011 ).
Studies in tetrapods on the relationship between ciliary bundle length and frequency
(e.g., Manley 2000 ; Arch et al. 2012 ) are in accordance with those in fi shes, i.e.
shorter bundles are more sensitive to higher frequencies. However, further studies
similar to the experiments with goldfi sh (Smith et al. 2011 ) are needed for other fi sh
species that lack ancillary auditory structures or any gas-fi lled bladders. Modeling
of the micromechanical behavior of different ciliary bundle types from the macula
utriculi of a red-eared turtle ( Trachemys ( Pseudemys ) scripta ) indicates that the
length ratio of the kinocilium (K) compared to the tallest stereovillus (S) infl uences
bundle stiffness and the magnitude of tensions of the tip links (=links connecting the
tips of stereovilli to each other) (Silber et al. 2004 ). Bundles in which the kinocilium
is only slightly longer than the tallest stereovillus are stiffer and tensions of tip links
are lower when the same force of defl ection is exerted than in bundles with a distinctly longer kinocilium compared to the tallest stereovillus. Ciliary bundles with a
large KS ratio were assumed to possess a wider operational range with respect to
bundle displacement but that they have lower sensitivities to bundle displacement
(Baird 1994 ).
Diversity of Inner Ears in Fishes: Possible Contribution Towards Hearing…