139
Calcite is also known to constitute the endogenous statoconia of the spined dogfi sh,
Squalus acanthias (Vilstrup 1951 ). Moreover, it was reported that the Zebrafi sh
otolith “switches from an aragonite polymorph to calcite polymorph with the
knockout of a single 613-amino acid protein ‘Startmaker’, named for the bizarre
and irregular type of otolith formed when the amino acid sequence of the protein is
changed,” (Berry 2004 ; see also Sollner et al. 2003 ). Fish with these altered otoliths
showed disorientation in fl owing water.
Surprisingly, also calcium oxalates can be involved in otolith development
of some mammals. Recently, Dror et al. ( 2010 ) reported for the fi rst time that
“calcium oxalate stones are formed in the mouse inner ear of a genetic model for
hearing loss and vestibular dysfunction in humans. A missense mutation within the
Slc26a4 gene abolishes the transport activity of its encoded protein, pendrin. As a
consequence, dramatic changes in mineral composition, size, and shape occur
within the utricle and saccule in a differential manner. Although abnormal giant
carbonate minerals reside in the utricle at all ages, in the saccule, a gradual change
in mineral composition leads to a formation of calcium oxalate in adult mice,”
(Dror et al. 2010 ).
Intriguingly, some fi sh possess magnetic microparticles in their otoliths as
well. For example, the saltwater ray has the inner ear gravity receptors that
contain mix phases of black coloured magnetic particles with white crystalline
otoconia. These are suggested to be some kind of the “ multidomains of magnetiteilmenite, ” (O’Leary et al. 1981 ). Also, the ventral region of sacculus of the
Fiddler Ray, or guitar fi sh (order Rhinobatiformes) contains magnetite particles
localized within the otolithic mass. As reported by Vilches-Troya et al. ( 1984 ):
“the exogenous magnetite particles differed from the endogenous otoconia both in
their capacity of orienting to magnetic fi elds, and their difference in mass due to
the higher atomic weight of iron. In addition to the normal gravistatic function of
the sacculus, two additional receptor functions are hypothesized based upon the
differences between the endogenous and exogenous otoconia,” (Vilches-Troya
et al. 1984 ).
These authors suggested that geomagnetic orientation of these animals is determined by a geomagnetic fi eld that could induce magnetite displacements detectable
by the hair cells. “Alternatively, the greater atomic weights of magnetite, relative to
that of otoconia, could result in gravitational and linear acceleration, which differed
in different regions of the macula,” (Vilches-Troya et al. 1984 ).
However, more surprisingly is the fact that some elasmobranchs, presumably those
having a wide ductus endolymphaticus, may use sea-sand as statoconia, a unique
feature within vertebrates (see for review Mills et al. 2011 ). Thus, Retzius ( 1881 )
observed irregular grains in the labyrinth of Acanthias , and Stewart ( 1903–1906 )
seems to have been the fi rst to identify these particles as sand. Exogenous statoconia
are also known to occur in different sharks and ray species. While some authors state
that the statoconia of these species consist of nothing but sand, others have found both
sand and endogenous statoconia and only endogenous statoconia in the same species.
This discrepancy may be due partly to varying proportions of the two constituents in
different species (Carlström 1963 ). “The otolithic apparatus of the dogfi sh can also
3.3 Otoconia and Otoliths
Calcite is also known to constitute the endogenous statoconia of the spined dogfi sh,
Squalus acanthias (Vilstrup 1951 ). Moreover, it was reported that the Zebrafi sh
otolith “switches from an aragonite polymorph to calcite polymorph with the
knockout of a single 613-amino acid protein ‘Startmaker’, named for the bizarre
and irregular type of otolith formed when the amino acid sequence of the protein is
changed,” (Berry 2004 ; see also Sollner et al. 2003 ). Fish with these altered otoliths
showed disorientation in fl owing water.
Surprisingly, also calcium oxalates can be involved in otolith development
of some mammals. Recently, Dror et al. ( 2010 ) reported for the fi rst time that
“calcium oxalate stones are formed in the mouse inner ear of a genetic model for
hearing loss and vestibular dysfunction in humans. A missense mutation within the
Slc26a4 gene abolishes the transport activity of its encoded protein, pendrin. As a
consequence, dramatic changes in mineral composition, size, and shape occur
within the utricle and saccule in a differential manner. Although abnormal giant
carbonate minerals reside in the utricle at all ages, in the saccule, a gradual change
in mineral composition leads to a formation of calcium oxalate in adult mice,”
(Dror et al. 2010 ).
Intriguingly, some fi sh possess magnetic microparticles in their otoliths as
well. For example, the saltwater ray has the inner ear gravity receptors that
contain mix phases of black coloured magnetic particles with white crystalline
otoconia. These are suggested to be some kind of the “ multidomains of magnetiteilmenite, ” (O’Leary et al. 1981 ). Also, the ventral region of sacculus of the
Fiddler Ray, or guitar fi sh (order Rhinobatiformes) contains magnetite particles
localized within the otolithic mass. As reported by Vilches-Troya et al. ( 1984 ):
“the exogenous magnetite particles differed from the endogenous otoconia both in
their capacity of orienting to magnetic fi elds, and their difference in mass due to
the higher atomic weight of iron. In addition to the normal gravistatic function of
the sacculus, two additional receptor functions are hypothesized based upon the
differences between the endogenous and exogenous otoconia,” (Vilches-Troya
et al. 1984 ).
These authors suggested that geomagnetic orientation of these animals is determined by a geomagnetic fi eld that could induce magnetite displacements detectable
by the hair cells. “Alternatively, the greater atomic weights of magnetite, relative to
that of otoconia, could result in gravitational and linear acceleration, which differed
in different regions of the macula,” (Vilches-Troya et al. 1984 ).
However, more surprisingly is the fact that some elasmobranchs, presumably those
having a wide ductus endolymphaticus, may use sea-sand as statoconia, a unique
feature within vertebrates (see for review Mills et al. 2011 ). Thus, Retzius ( 1881 )
observed irregular grains in the labyrinth of Acanthias , and Stewart ( 1903–1906 )
seems to have been the fi rst to identify these particles as sand. Exogenous statoconia
are also known to occur in different sharks and ray species. While some authors state
that the statoconia of these species consist of nothing but sand, others have found both
sand and endogenous statoconia and only endogenous statoconia in the same species.
This discrepancy may be due partly to varying proportions of the two constituents in
different species (Carlström 1963 ). “The otolithic apparatus of the dogfi sh can also
3.3 Otoconia and Otoliths