380
5 Inner Ear Diversity in the Light of Phylogeny
Modifi cations of inner ears and/or ancillary auditory structures might be to some
extent linked to phylogenetic constraints or may represent a phylogenetic “legacy.”
Including a phylogenetic perspective is thus an important prerequisite to test any
evolutionary hypothesis regarding the evolution of the auditory periphery and audition (e.g., Braun et al. 2012 ; Deng et al. 2013 ). A recent study by Deng et al. ( 2013 )
on the inner ear morphology of melamphaid fi shes demonstrated the importance of
such an approach. The melamphaid Scopelogadus mizolepis bispinosus has a
simple- shaped round saccular otolith lacking the spur-like structure characterizing
Melamphaes and Poromitra . Without phylogenetic background, it is tempting to
speculate that the round saccular otolith in Scopelogadus represents the plesiomorphic condition. When saccular morphology is plotted on a phylogeny (based on the
mitochondrial COI gene) that identifi es Melamphaes and Scopelogadus to be more
closely related to each other than to Poromitra , the round otolith without spur could
equally be interpreted as a derived character, i.e. the spur was secondarily lost in
Scopelogadus (Deng et al. 2013 ).
A promising model to study inner ear evolution based on a phylogenetic hypothesis is the speciose family Cichlidae, whose phylogenetic relationships have been
intensively studied (Sparks and Smith 2004 ; Azuma et al. 2008 ; Sparks 2008 ;
McMahan et al. 2013 ). Future studies on inner ear morphology with focus on the
macula shape and ciliary bundle orientations within the cichlid genus Paretroplus ,
but also of the whole cichlid subfamily Ptychochrominae, would be highly interesting (Fig. 7 ) because a rather robust phylogeny exists for them (Sparks 2004 ; Sparks
and Smith 2004 ; McMahan et al. 2013 ). The Ptychochrominae display different
swim bladder morphologies ranging from bladders without anterior extensions
( Katria ) via short extensions to extensions that abut the posterior skull ( Paratilapia )
(Sparks 2008 ; Schulz-Mirbach et al. 2012 ). In combination with extensive ecoacoustical data from the habitats of these species (see Braun et al. 2012 ), this may help
enlighten the evolution of the maculae and orientation patterns in this subfamily and
the amount of coevolution between inner ear morphology, ancillary auditory structures and hearing abilities.
6 What Factors May Have Infl uenced the Evolution
of the Auditory Periphery?
Driving factors in the evolution of the auditory periphery (here: inner ears and ancillary auditory structures) in fi shes are clearly those linked to audition. Fishes may
gain information from the auditory scene in their habitat that is crucial for survival
(e.g., avoidance of predators) or their reproductive success (e.g., detection of vocalizing mates). Abiotic (waves, water turbulences, etc.) and biotic (predators, prey,
conspecifi cs) sound sources, i.e. the acoustical environment, should thus play an
T. Schulz-Mirbach and F. Ladich
5 Inner Ear Diversity in the Light of Phylogeny
Modifi cations of inner ears and/or ancillary auditory structures might be to some
extent linked to phylogenetic constraints or may represent a phylogenetic “legacy.”
Including a phylogenetic perspective is thus an important prerequisite to test any
evolutionary hypothesis regarding the evolution of the auditory periphery and audition (e.g., Braun et al. 2012 ; Deng et al. 2013 ). A recent study by Deng et al. ( 2013 )
on the inner ear morphology of melamphaid fi shes demonstrated the importance of
such an approach. The melamphaid Scopelogadus mizolepis bispinosus has a
simple- shaped round saccular otolith lacking the spur-like structure characterizing
Melamphaes and Poromitra . Without phylogenetic background, it is tempting to
speculate that the round saccular otolith in Scopelogadus represents the plesiomorphic condition. When saccular morphology is plotted on a phylogeny (based on the
mitochondrial COI gene) that identifi es Melamphaes and Scopelogadus to be more
closely related to each other than to Poromitra , the round otolith without spur could
equally be interpreted as a derived character, i.e. the spur was secondarily lost in
Scopelogadus (Deng et al. 2013 ).
A promising model to study inner ear evolution based on a phylogenetic hypothesis is the speciose family Cichlidae, whose phylogenetic relationships have been
intensively studied (Sparks and Smith 2004 ; Azuma et al. 2008 ; Sparks 2008 ;
McMahan et al. 2013 ). Future studies on inner ear morphology with focus on the
macula shape and ciliary bundle orientations within the cichlid genus Paretroplus ,
but also of the whole cichlid subfamily Ptychochrominae, would be highly interesting (Fig. 7 ) because a rather robust phylogeny exists for them (Sparks 2004 ; Sparks
and Smith 2004 ; McMahan et al. 2013 ). The Ptychochrominae display different
swim bladder morphologies ranging from bladders without anterior extensions
( Katria ) via short extensions to extensions that abut the posterior skull ( Paratilapia )
(Sparks 2008 ; Schulz-Mirbach et al. 2012 ). In combination with extensive ecoacoustical data from the habitats of these species (see Braun et al. 2012 ), this may help
enlighten the evolution of the maculae and orientation patterns in this subfamily and
the amount of coevolution between inner ear morphology, ancillary auditory structures and hearing abilities.
6 What Factors May Have Infl uenced the Evolution
of the Auditory Periphery?
Driving factors in the evolution of the auditory periphery (here: inner ears and ancillary auditory structures) in fi shes are clearly those linked to audition. Fishes may
gain information from the auditory scene in their habitat that is crucial for survival
(e.g., avoidance of predators) or their reproductive success (e.g., detection of vocalizing mates). Abiotic (waves, water turbulences, etc.) and biotic (predators, prey,
conspecifi cs) sound sources, i.e. the acoustical environment, should thus play an
T. Schulz-Mirbach and F. Ladich