61
2 Anatomy Associated with the Reception
of Acoustic Stimuli
Butterfl yfi shes have a well-developed lateral line canal system on the head and
trunk and have an ear that is typical of those teleost fi shes that lack otophysic connections (a swim bladder-ear connection). The laterophysic connection, a unique
feature of the genus Chaetodon , demonstrates a considerable degree of variation
among species, and the morphology of the swim bladder is correlated with that of
the laterophysic connection.
2.1 The Laterophysic Connection
The “laterophysic connection” (LC), the association of anterior swim bladder horns
with an opening in the lateral line canal contained within the supracleithral bone,
was named to draw attention to its apparent structural and putative functional similarity to otophysic connections found in other fi shes. Webb ( 1998 ) suggested that
the LC is the site of transduction of pressure oscillations generated by sound pressure
waves in the air-fi lled swim bladder and swim bladder horns into fl uid movements
in the lateral line canal in the supracleithral bone, which are capable of stimulating
canal neuromasts just rostral and caudal to the LC. It was hypothesized that the
presence of an LC in Chaetodon would thus make the lateral line system, in addition
to the inner ear (by virtue of the proximity of the swim bladder horns to the otic
capsule), sensitive to sound pressure, thus expanding its functional repertoire. It
was further suggested that novel interactions of lateral line and auditory input would
enhance the interpretation of acoustic stimuli (Webb 1998 ; Webb et al. 2006 ), and
the reception of acoustic communication stimuli produced by Chaetodon in their
natural coral reef habitats (Tricas et al. 2006 ; see Sect. 3 ).
LC morphology varies interspecifi cally but, like the external body features of
butterfl yfi shes, is not sexually dimorphic (Webb and Smith 2000 ). Two LC types are
found among Chaetodon species (Figs. 3 and 4 ): (1) a Direct LC, characterized by
direct contact of the lateral wall of the cylindrical anterior swim bladder horns with
the medial opening in the supracleithrum, and (2) an Indirect LC, defi ned by the
presence of muscle or kidney tissue between the lateral wall of the anterior swim
bladder horn and the medial opening in the supracleithrum (Webb and Smith 2000 ).
Two variants on a direct LC (Dir1 and Dir2) and four variants on an indirect LC
(Ind1–Ind4) were found among 22 Chaetodon species in the 11 Chaetodon subgenera
(Smith et al. 2003 ; Webb et al. 2006 , Figs. 3 and 4 ; Table 1 ). These variants are
defi ned by the type(s) of tissues found between the swim bladder horns and the
supracleithrum (presence or absence of mucoid connective tissue in the medial
opening), the length and diameter of the swim bladder horns (long [~1.5–3.5 mm]
vs. short [<1 mm] horns, wide [~1–3 mm] vs. narrow [<1 mm] horns; Fig. 4 ), and
the presence or absence of an external constriction ( ductus communicans ) of the
Acoustic Communication in Butterfl yfi shes…
2 Anatomy Associated with the Reception
of Acoustic Stimuli
Butterfl yfi shes have a well-developed lateral line canal system on the head and
trunk and have an ear that is typical of those teleost fi shes that lack otophysic connections (a swim bladder-ear connection). The laterophysic connection, a unique
feature of the genus Chaetodon , demonstrates a considerable degree of variation
among species, and the morphology of the swim bladder is correlated with that of
the laterophysic connection.
2.1 The Laterophysic Connection
The “laterophysic connection” (LC), the association of anterior swim bladder horns
with an opening in the lateral line canal contained within the supracleithral bone,
was named to draw attention to its apparent structural and putative functional similarity to otophysic connections found in other fi shes. Webb ( 1998 ) suggested that
the LC is the site of transduction of pressure oscillations generated by sound pressure
waves in the air-fi lled swim bladder and swim bladder horns into fl uid movements
in the lateral line canal in the supracleithral bone, which are capable of stimulating
canal neuromasts just rostral and caudal to the LC. It was hypothesized that the
presence of an LC in Chaetodon would thus make the lateral line system, in addition
to the inner ear (by virtue of the proximity of the swim bladder horns to the otic
capsule), sensitive to sound pressure, thus expanding its functional repertoire. It
was further suggested that novel interactions of lateral line and auditory input would
enhance the interpretation of acoustic stimuli (Webb 1998 ; Webb et al. 2006 ), and
the reception of acoustic communication stimuli produced by Chaetodon in their
natural coral reef habitats (Tricas et al. 2006 ; see Sect. 3 ).
LC morphology varies interspecifi cally but, like the external body features of
butterfl yfi shes, is not sexually dimorphic (Webb and Smith 2000 ). Two LC types are
found among Chaetodon species (Figs. 3 and 4 ): (1) a Direct LC, characterized by
direct contact of the lateral wall of the cylindrical anterior swim bladder horns with
the medial opening in the supracleithrum, and (2) an Indirect LC, defi ned by the
presence of muscle or kidney tissue between the lateral wall of the anterior swim
bladder horn and the medial opening in the supracleithrum (Webb and Smith 2000 ).
Two variants on a direct LC (Dir1 and Dir2) and four variants on an indirect LC
(Ind1–Ind4) were found among 22 Chaetodon species in the 11 Chaetodon subgenera
(Smith et al. 2003 ; Webb et al. 2006 , Figs. 3 and 4 ; Table 1 ). These variants are
defi ned by the type(s) of tissues found between the swim bladder horns and the
supracleithrum (presence or absence of mucoid connective tissue in the medial
opening), the length and diameter of the swim bladder horns (long [~1.5–3.5 mm]
vs. short [<1 mm] horns, wide [~1–3 mm] vs. narrow [<1 mm] horns; Fig. 4 ), and
the presence or absence of an external constriction ( ductus communicans ) of the
Acoustic Communication in Butterfl yfi shes…