382
and Malicki 2007 ). Certain mutations that would result in new, modifi ed and possibly “more optimized” ear morphologies may negatively affect other structures for
survival and thus could not be realized in a living animal. This, in turn, would mean
that again only a limited number of ear modifi cations are possible.
Finally, sensory trade-offs may be important when fi shes inhabit extreme habitats such as the deep-sea, characterized by perpetual darkness and food scarcity.
Depending on the mode of life, i.e. as scavenger, predator on large (e.g., other
fi shes) or small prey (e.g., plankton), different senses like olfaction and gustation in
a scavenger, enlarged eyes, or improved audition may compensate for the lack of
visual input. In macrourid species, Deng ( 2009 ) found smaller maculae in the species still primarily relying on vision, whereas the only vocal species studied showed
a large macula sacculi and saccular otolith. These fi ndings could be interpreted as
sensory trade-offs in which one sense is improved at the cost of another due to
energy limitation (Deng 2009 ).
7 Conclusions and Outlook
Inner ear diversity of bony fi shes may partly be linked to the presence of ancillary
auditory structures; but phylogenetic relationships or adaptation to extreme ecological conditions as found in deep-sea habitats or the ecoacoustical environment may
also have contributed to this diversity. Selective forces or constraints acting on inner
ear evolution are still poorly understood. This paucity of knowledge is evident when
trying to explain the potential functional role and evolution of the different orientation patterns on the macula sacculi. Although it is very likely that this diversity of
orientation patterns serves in audition, we have insuffi cient data to infer which auditory functions (e.g., sound localization) are facilitated by which pattern type. It is
also possible that the same or similar auditory tasks are enabled by different pattern
types. Certain pattern types or variation in ciliary bundle morphology may also be
linked to (1) different ecological conditions such as high water pressures in the deep
sea or the ability to detect faint noise in a quiet water body or (2) to solve different
tasks in sound communication (short-range vs. long-range communication or sound
detection). Despite the diversity of the auditory periphery, the currently available
data point to only a limited number of morphological modifi cations that result in
hearing enhancement; this is refl ected in the “only” fi ve orientation patterns on the
macula sacculi, of which the vertical, the opposing and modifi cations of the alternating patterns can be assigned to improved audition. Different selective pressures
may have favored either the “vertical pattern” or certain patterns combining horizontal and vertical orientation groups.
Future research should focus on:
1. Evaluating the differences in ear morphology of (closely related) species with
and without ancillary auditory structures, especially with regard to shape, curvaT. Schulz-Mirbach and F. Ladich
and Malicki 2007 ). Certain mutations that would result in new, modifi ed and possibly “more optimized” ear morphologies may negatively affect other structures for
survival and thus could not be realized in a living animal. This, in turn, would mean
that again only a limited number of ear modifi cations are possible.
Finally, sensory trade-offs may be important when fi shes inhabit extreme habitats such as the deep-sea, characterized by perpetual darkness and food scarcity.
Depending on the mode of life, i.e. as scavenger, predator on large (e.g., other
fi shes) or small prey (e.g., plankton), different senses like olfaction and gustation in
a scavenger, enlarged eyes, or improved audition may compensate for the lack of
visual input. In macrourid species, Deng ( 2009 ) found smaller maculae in the species still primarily relying on vision, whereas the only vocal species studied showed
a large macula sacculi and saccular otolith. These fi ndings could be interpreted as
sensory trade-offs in which one sense is improved at the cost of another due to
energy limitation (Deng 2009 ).
7 Conclusions and Outlook
Inner ear diversity of bony fi shes may partly be linked to the presence of ancillary
auditory structures; but phylogenetic relationships or adaptation to extreme ecological conditions as found in deep-sea habitats or the ecoacoustical environment may
also have contributed to this diversity. Selective forces or constraints acting on inner
ear evolution are still poorly understood. This paucity of knowledge is evident when
trying to explain the potential functional role and evolution of the different orientation patterns on the macula sacculi. Although it is very likely that this diversity of
orientation patterns serves in audition, we have insuffi cient data to infer which auditory functions (e.g., sound localization) are facilitated by which pattern type. It is
also possible that the same or similar auditory tasks are enabled by different pattern
types. Certain pattern types or variation in ciliary bundle morphology may also be
linked to (1) different ecological conditions such as high water pressures in the deep
sea or the ability to detect faint noise in a quiet water body or (2) to solve different
tasks in sound communication (short-range vs. long-range communication or sound
detection). Despite the diversity of the auditory periphery, the currently available
data point to only a limited number of morphological modifi cations that result in
hearing enhancement; this is refl ected in the “only” fi ve orientation patterns on the
macula sacculi, of which the vertical, the opposing and modifi cations of the alternating patterns can be assigned to improved audition. Different selective pressures
may have favored either the “vertical pattern” or certain patterns combining horizontal and vertical orientation groups.
Future research should focus on:
1. Evaluating the differences in ear morphology of (closely related) species with
and without ancillary auditory structures, especially with regard to shape, curvaT. Schulz-Mirbach and F. Ladich