342
namely the otoliths or otoconia (Platt and Popper 1981a ). Despite the partly extensive (gross) morphological studies, details about the arrangement of sensory hair
cells expressed in the ciliary bundle orientation patterns remained uninvestigated
until Popper’s discovery that particularly oriented ciliary bundles are arranged in
groups on the maculae of the lake whitefi sh Coregonus clupeaformis (Popper 1976 ).
Follow-up studies revealed that teleost fi shes exhibit a considerable variety of orientation patterns on the macula of the saccule and partly on the macula of the lagena,
but less so on the macula of the utricle and almost none on the cristae.
Since Retzius’ study (Retzius 1881 ), detailed documentation of the inner ear morphology tremendously increased over the past 40 years. The result is solid knowledge
about the range of inner ear diversity within bony fi shes. In contrast, our understanding
of fi sh hearing abilities other than hearing bandwidth and auditory thresholds is still
fragmentary. This is in part due to methodological shortcomings that, at present, hinder
an unambiguous differentiation of the amount of inner ear stimulation through particle
motion and pressure at different frequencies (Popper and Fay 2011 ; Ladich and Fay
2013 ). This makes it diffi cult to assign certain modifi cations of the inner ear or different
inner ear morphology in closely related taxa to specifi c physiological functions.
Moreover, even less is known about the potential selective pressures and constraints
acting on inner ear evolution of bony fi shes. This leaves unanswered the central question
of why this exceptional diversity of ears in bony fi shes, especially in teleosts, exists.
Many aspects of inner ear diversity could be discussed. In this review, however, we
concentrate on the sensory epithelia because they are the sensory “unit” of the inner
ear that is probably most intimately tied to auditory tasks. The purpose of our review
is therefore twofold. The fi rst is a recent overview of inner ear diversity in bony fi shes
with a focus on sensory epithelia, especially on maculae (macula sacculi and macula
lagenae); the latter display most of the variability among the inner ear’s sensory epithelia (e.g., Platt and Popper 1981a ; Popper and Schilt 2008 ). Second, we discuss the
assumption that inner ear diversity is linked to the presence of ancillary auditory structures and examine which underlying factors may have affected inner ear evolution.
We ask whether the orientation pattern diversity reveals differences in auditory tasks
in bony fi shes, and we discuss how this diversity may have evolved in bony fi shes
(Platt and Popper 1981a ; Popper and Coombs 1982 ; Ladich and Popper 2004 ).
2 Diversity in Inner Ears
Though there is no “one” ear among bony fi shes, a basic ear structure can be identifi ed: an upper inner ear consisting of three semicircular canals and the utricle, and a
lower inner ear comprising the saccule and the lagena (Fig. 1 ) (Popper 2011 ; Popper
Fig. 1 (continued) especially in the saccule and lagena. Some species, however, like Eutrigla gurnardus ( e ) are characterized by distinctly large semicircular canals. All ears are shown in medial
view. Illustrations were modifi ed from Ladich and Popper ( 2001 , 2004 ), Lu and Popper ( 1998 ),
Retzius ( 1881 ), and Schulz-Mirbach et al. ( 2011 ). a anterior, cc common canal, d dorsal, sc semicircular canal. Copyright 1998 (1C) and 2001 (1D), with kind permission from Elsevier
T. Schulz-Mirbach and F. Ladich
namely the otoliths or otoconia (Platt and Popper 1981a ). Despite the partly extensive (gross) morphological studies, details about the arrangement of sensory hair
cells expressed in the ciliary bundle orientation patterns remained uninvestigated
until Popper’s discovery that particularly oriented ciliary bundles are arranged in
groups on the maculae of the lake whitefi sh Coregonus clupeaformis (Popper 1976 ).
Follow-up studies revealed that teleost fi shes exhibit a considerable variety of orientation patterns on the macula of the saccule and partly on the macula of the lagena,
but less so on the macula of the utricle and almost none on the cristae.
Since Retzius’ study (Retzius 1881 ), detailed documentation of the inner ear morphology tremendously increased over the past 40 years. The result is solid knowledge
about the range of inner ear diversity within bony fi shes. In contrast, our understanding
of fi sh hearing abilities other than hearing bandwidth and auditory thresholds is still
fragmentary. This is in part due to methodological shortcomings that, at present, hinder
an unambiguous differentiation of the amount of inner ear stimulation through particle
motion and pressure at different frequencies (Popper and Fay 2011 ; Ladich and Fay
2013 ). This makes it diffi cult to assign certain modifi cations of the inner ear or different
inner ear morphology in closely related taxa to specifi c physiological functions.
Moreover, even less is known about the potential selective pressures and constraints
acting on inner ear evolution of bony fi shes. This leaves unanswered the central question
of why this exceptional diversity of ears in bony fi shes, especially in teleosts, exists.
Many aspects of inner ear diversity could be discussed. In this review, however, we
concentrate on the sensory epithelia because they are the sensory “unit” of the inner
ear that is probably most intimately tied to auditory tasks. The purpose of our review
is therefore twofold. The fi rst is a recent overview of inner ear diversity in bony fi shes
with a focus on sensory epithelia, especially on maculae (macula sacculi and macula
lagenae); the latter display most of the variability among the inner ear’s sensory epithelia (e.g., Platt and Popper 1981a ; Popper and Schilt 2008 ). Second, we discuss the
assumption that inner ear diversity is linked to the presence of ancillary auditory structures and examine which underlying factors may have affected inner ear evolution.
We ask whether the orientation pattern diversity reveals differences in auditory tasks
in bony fi shes, and we discuss how this diversity may have evolved in bony fi shes
(Platt and Popper 1981a ; Popper and Coombs 1982 ; Ladich and Popper 2004 ).
2 Diversity in Inner Ears
Though there is no “one” ear among bony fi shes, a basic ear structure can be identifi ed: an upper inner ear consisting of three semicircular canals and the utricle, and a
lower inner ear comprising the saccule and the lagena (Fig. 1 ) (Popper 2011 ; Popper
Fig. 1 (continued) especially in the saccule and lagena. Some species, however, like Eutrigla gurnardus ( e ) are characterized by distinctly large semicircular canals. All ears are shown in medial
view. Illustrations were modifi ed from Ladich and Popper ( 2001 , 2004 ), Lu and Popper ( 1998 ),
Retzius ( 1881 ), and Schulz-Mirbach et al. ( 2011 ). a anterior, cc common canal, d dorsal, sc semicircular canal. Copyright 1998 (1C) and 2001 (1D), with kind permission from Elsevier
T. Schulz-Mirbach and F. Ladich