378
of otophysans and mormyrids (Fig. 4a, d, e ), the opposing pattern of anabantiform
fi shes (Fig. 4b ) or “unique” patterns (see Antimora ; Fig. 5b ) that cannot be assigned
to one of the fi ve patterns (Table 2 ). It is conceivable that the inner ear in such species and ancillary auditory structures coevolved to some degree to guarantee fi netuning between these two units to improve audition.
In some cases, however, ancillary structures and modifi ed orientation patterns—
deviating from the standard or dual patterns—are present but without distinctly
improved hearing compared to species that lack these accessory structures. The
Clown knifefi sh Chitala chitala , for example, does not show an expanded hearing
bandwidth or higher auditory sensitivities (Coombs and Popper 1982 ), and the sciaenid species Micropogonias undulates and Cynoscion nebulosus show a slightly
expanded bandwidth but similar auditory sensitivities as species without anterior
swim bladder extensions (Horodysky et al. 2008 ). Moreover, ancillary auditory
structures and improved auditory abilities do not necessarily correlate with modifi ed (more complex) orientation patterns on the maculae, as demonstrated for the
Hawaiian ladyfi sh Elops hawaiensis (Elopidae) (Popper 1981 ) and the cichlid
Etroplus maculatus : they have “standard” patterns on all three macula types (when
analyzing artifi cially fl attened maculae; compare Fig. 7a to Fig. 6a ) (SchulzMirbach et al. 2014 ). A distinct 3D curvature bringing the ciliary bundles in new
spatial orientation without modifi cations of the orientation patterns in 2D is present
in E. maculatus . The anterior arm of its macula lagenae and the lacinia of the macula utriculi are strongly curved. The wider range of directions of ciliary bundles
based on the 3D curvature—a condition also found in the macula sacculi of the silver perch Bairdiella chrysoura (Sciaenidae)—might translate into a wider range of
directional stimuli being detectible, and thus may play a role in localizing sound
sources (Schulz- Mirbach et al. 2014 ). Finally, species such as the cod Gadus
morhua were shown to be pressure sensitive without any obvious morphological
modifi cations of the auditory periphery (see Hawkins 1993 ); cod lacks swim bladder extensions and possesses a dual pattern on the macula sacculi. The cichlid
Hemichromis guttatus seems to be another example of a species lacking morphological specializations while displaying an expanded hearing bandwidth comparable to that of E. maculatus .
Generally, more experimental data about hearing in fi shes will be necessary
before defi nitively answering questions of how inner ear morphology is linked to
physiology (see Popper and Fay 2011 ). So far, most knowledge refers to auditory
thresholds and hearing bandwidth in a variety of species (see Fay 1988 ; Ladich and
Fay 2013 ). Data on frequency discrimination, tuning, and detection of directional
stimuli are limited to only a few species such as Porichthys notatus , goldfi sh and
Opsanus tau . They hardly cover the full range of inner ear diversity (Fay and EddsWalton 1997 ; Edds-Walton et al. 1999 ; Sisneros 2007 ; Smith et al. 2011 ; Zeddies
et al. 2012 ) and thus do not allow drawing conclusions about the correlation between
orientation pattern diversity and these auditory parameters. Hence, more sophisticated comparative physiological measurements are needed for a deeper understandT. Schulz-Mirbach and F. Ladich
of otophysans and mormyrids (Fig. 4a, d, e ), the opposing pattern of anabantiform
fi shes (Fig. 4b ) or “unique” patterns (see Antimora ; Fig. 5b ) that cannot be assigned
to one of the fi ve patterns (Table 2 ). It is conceivable that the inner ear in such species and ancillary auditory structures coevolved to some degree to guarantee fi netuning between these two units to improve audition.
In some cases, however, ancillary structures and modifi ed orientation patterns—
deviating from the standard or dual patterns—are present but without distinctly
improved hearing compared to species that lack these accessory structures. The
Clown knifefi sh Chitala chitala , for example, does not show an expanded hearing
bandwidth or higher auditory sensitivities (Coombs and Popper 1982 ), and the sciaenid species Micropogonias undulates and Cynoscion nebulosus show a slightly
expanded bandwidth but similar auditory sensitivities as species without anterior
swim bladder extensions (Horodysky et al. 2008 ). Moreover, ancillary auditory
structures and improved auditory abilities do not necessarily correlate with modifi ed (more complex) orientation patterns on the maculae, as demonstrated for the
Hawaiian ladyfi sh Elops hawaiensis (Elopidae) (Popper 1981 ) and the cichlid
Etroplus maculatus : they have “standard” patterns on all three macula types (when
analyzing artifi cially fl attened maculae; compare Fig. 7a to Fig. 6a ) (SchulzMirbach et al. 2014 ). A distinct 3D curvature bringing the ciliary bundles in new
spatial orientation without modifi cations of the orientation patterns in 2D is present
in E. maculatus . The anterior arm of its macula lagenae and the lacinia of the macula utriculi are strongly curved. The wider range of directions of ciliary bundles
based on the 3D curvature—a condition also found in the macula sacculi of the silver perch Bairdiella chrysoura (Sciaenidae)—might translate into a wider range of
directional stimuli being detectible, and thus may play a role in localizing sound
sources (Schulz- Mirbach et al. 2014 ). Finally, species such as the cod Gadus
morhua were shown to be pressure sensitive without any obvious morphological
modifi cations of the auditory periphery (see Hawkins 1993 ); cod lacks swim bladder extensions and possesses a dual pattern on the macula sacculi. The cichlid
Hemichromis guttatus seems to be another example of a species lacking morphological specializations while displaying an expanded hearing bandwidth comparable to that of E. maculatus .
Generally, more experimental data about hearing in fi shes will be necessary
before defi nitively answering questions of how inner ear morphology is linked to
physiology (see Popper and Fay 2011 ). So far, most knowledge refers to auditory
thresholds and hearing bandwidth in a variety of species (see Fay 1988 ; Ladich and
Fay 2013 ). Data on frequency discrimination, tuning, and detection of directional
stimuli are limited to only a few species such as Porichthys notatus , goldfi sh and
Opsanus tau . They hardly cover the full range of inner ear diversity (Fay and EddsWalton 1997 ; Edds-Walton et al. 1999 ; Sisneros 2007 ; Smith et al. 2011 ; Zeddies
et al. 2012 ) and thus do not allow drawing conclusions about the correlation between
orientation pattern diversity and these auditory parameters. Hence, more sophisticated comparative physiological measurements are needed for a deeper understandT. Schulz-Mirbach and F. Ladich