383
ture of the macula and the orientation patterns of ciliary bundles (Ramcharitar
et al. 2001 ; Schulz-Mirbach et al. 2014 ). The ontogenetic development of the
ear, ancillary auditory structures and audition of such (closely related) species is
an additional promising fi eld of study.
2. Development and application of physiological/experimental measurements with
respect to hearing abilities other than bandwidth and sensitivity and of inner ear
physiology in general. Moreover, more studies on closely related species (differing in ancillary auditory structures) are needed to relate inner ear morphology to
(1) directional responses of different hair cell orientations (e.g., Lu and Popper
2001 ), (2) the ability of sound source localization, and (3) potential tonotopic
frequency selectivity (e.g., Smith et al. 2011 ). It is important that these comparative studies also incorporate a phylogenetic approach to disentangle which inner
ear characters and certain auditory abilities are plesiomorphic and which are
more apomorphic.
3. The genetic background especially regarding the formation of differently oriented ciliary bundle groups on the maculae (Sienknecht 2013 ; Sienknecht et al.
2014 ) and the genetic control of the development of inner ears and ancillary
auditory structures which may exert constraints on inner ear variability.
4. Evaluating the amount of coevolution of sound production and inner ear morphology in vocal species as indicated by seasonal plasticity in the number of
sensory hair cells in females of the plainfi n midshipman or large saccular otoliths
in some ophidiiform species or Nezumia aequalis (Parmentier et al. 2001 ; Deng
2009 ; Sisneros 2009 ; Coffi n et al. 2012 ; Kéver et al. 2014 ).
5. The role of natural ambient noise on the evolution of hearing abilities and inner
ear morphology by (1) measuring ambient noise levels in the fi eld and testing
whether hearing abilities of species living in the respective habitats can be correlated with these ambient noise levels (Amoser and Ladich 2005 ; Ladich 2014a )
and (2) evaluating the contribution of inner ears/inner ear components to auditory tasks like auditory scene analysis or short range vs. long range sound
detection.
6. “Comparative” modeling (Finneran and Hastings 2000 ; Rodgers and Rogers
2011 ; Krysl et al. 2012 ) of the movement of inner ear components and accessory
structures based on 3D models of species with and without ancillary auditory
structures. Cichlids may provide a suitable model for such investigations. A better understanding of the mechanical interactions of inner ear components and
ancillary auditory structures may provide the basis for testing adaptive vs. nonadaptive evolutionary hypotheses.
7. In vivo measurements of the movement of the different parts of the auditory
periphery, i.e. of the otolith relative to the macula, the transmission of oscillation
of gas-fi lled bladders to the surrounding tissue, skull bone, perilymphatic spaces,
or the endolymph. This would be indispensable for a better functional morphological understanding (Sand and Michelsen 1978 ; Finneran and Hastings 2000 ;
Chen et al. 2011 ).
Diversity of Inner Ears in Fishes: Possible Contribution Towards Hearing…
ture of the macula and the orientation patterns of ciliary bundles (Ramcharitar
et al. 2001 ; Schulz-Mirbach et al. 2014 ). The ontogenetic development of the
ear, ancillary auditory structures and audition of such (closely related) species is
an additional promising fi eld of study.
2. Development and application of physiological/experimental measurements with
respect to hearing abilities other than bandwidth and sensitivity and of inner ear
physiology in general. Moreover, more studies on closely related species (differing in ancillary auditory structures) are needed to relate inner ear morphology to
(1) directional responses of different hair cell orientations (e.g., Lu and Popper
2001 ), (2) the ability of sound source localization, and (3) potential tonotopic
frequency selectivity (e.g., Smith et al. 2011 ). It is important that these comparative studies also incorporate a phylogenetic approach to disentangle which inner
ear characters and certain auditory abilities are plesiomorphic and which are
more apomorphic.
3. The genetic background especially regarding the formation of differently oriented ciliary bundle groups on the maculae (Sienknecht 2013 ; Sienknecht et al.
2014 ) and the genetic control of the development of inner ears and ancillary
auditory structures which may exert constraints on inner ear variability.
4. Evaluating the amount of coevolution of sound production and inner ear morphology in vocal species as indicated by seasonal plasticity in the number of
sensory hair cells in females of the plainfi n midshipman or large saccular otoliths
in some ophidiiform species or Nezumia aequalis (Parmentier et al. 2001 ; Deng
2009 ; Sisneros 2009 ; Coffi n et al. 2012 ; Kéver et al. 2014 ).
5. The role of natural ambient noise on the evolution of hearing abilities and inner
ear morphology by (1) measuring ambient noise levels in the fi eld and testing
whether hearing abilities of species living in the respective habitats can be correlated with these ambient noise levels (Amoser and Ladich 2005 ; Ladich 2014a )
and (2) evaluating the contribution of inner ears/inner ear components to auditory tasks like auditory scene analysis or short range vs. long range sound
detection.
6. “Comparative” modeling (Finneran and Hastings 2000 ; Rodgers and Rogers
2011 ; Krysl et al. 2012 ) of the movement of inner ear components and accessory
structures based on 3D models of species with and without ancillary auditory
structures. Cichlids may provide a suitable model for such investigations. A better understanding of the mechanical interactions of inner ear components and
ancillary auditory structures may provide the basis for testing adaptive vs. nonadaptive evolutionary hypotheses.
7. In vivo measurements of the movement of the different parts of the auditory
periphery, i.e. of the otolith relative to the macula, the transmission of oscillation
of gas-fi lled bladders to the surrounding tissue, skull bone, perilymphatic spaces,
or the endolymph. This would be indispensable for a better functional morphological understanding (Sand and Michelsen 1978 ; Finneran and Hastings 2000 ;
Chen et al. 2011 ).
Diversity of Inner Ears in Fishes: Possible Contribution Towards Hearing…