65
(Woods 2006 ; Woods et al. 2006 ; Webb et al. 2006 ). The swim bladder is bounded
dorsally by the vertebral column, laterally by the ribs, and ventrally by the peritoneum that lines the abdominal cavity. This confi guration limits the overall shape and
volume of the swim bladder as indicated by the obvious indentations in the volume
of air created by the ribs (Webb et al. 2006 ; Fig. 1c ). Neither extrinsic nor intrinsic
sonic muscles are found in association with the swim bladder, so the swim bladder
likely functions as a sound resonator, which is stimulated by the physical motion of
other adjacent sound production mechanisms (Sect. 3 below).
Variation in the morphology of the swim bladder may have implications for both
bioacoustic reception and sound production. The gross morphology of the swim
bladder varies among Chaetodon species (such variation within a genus is unusual
and thus notable), and is correlated with LC type (Direct, Indirect; with a few minor
exceptions; Webb 1998 ; Webb and Smith 2000 ; Smith et al. 2003 ; Fig. 4 ). Chaetodon
species with a Direct LC (e.g., C. auriga , C. octofasciatus ) have a swim bladder
with a distinct “kink” in its long axis, such that the anterior half of the swim bladder
and swim bladder horns is relatively horizontal, whereas the posterior half of the
swim bladder is more vertical in orientation. The thick tunica externa is composed
of multiple layers of collagen and is somewhat thicker dorsally than it is ventrally
(Woods 2006 ). The ventral surface of the swim bladder is covered by a thin peritoneum (lining of the abdominal cavity) that wraps tightly around the swim bladder’s
posterior end (a “free” swim bladder; Smith et al. 2003 ). The thickness of the lateral
wall of the swim bladder horns decreases quite dramatically near the medial opening in the supracleithrum (Woods 2006 ), which may allow pressure-induced movement of the tissue covering the opening resulting in movements of fl uids in the
canal. Sound production by Chaetodon species with a direct LC is so far quantifi ed
only in C. auriga (very low frequency pulse sounds; Sect. 3 ). In addition, the
enhanced auditory sensitivity of C. auriga appears to depend more on the swim
bladder horns rather than on the body of the swim bladder (Sect. 4 ).
In contrast, Chaetodon species with an Indirect LC (e.g., C. multicinctus , C.
unimaculatus , C. kleinii , C. ornatissimus ), and species in non- Chaetodon genera
( Forcipiger , Heniochus and Hemitaurichthys ) have a swim bladder that is more
smoothly contoured (lacking a “kink”). The tunica externa in these species is much
thinner overall (and translucent) when compared to that in species with a direct
LC. It is thinner dorsally than it is ventrally, but its thickness does not vary along the
length of the swim bladder or along the horns as in species with a Direct LC (Woods
2006 ). In contrast to species with Direct LC, a thick, opaque peritoneum covers the
ventral surface of the swim bladder and attaches laterally to the ribs (an “attached”
swim bladder; Smith et al. 2003 ; Webb et al. 2006 ). In several Chaetodon species
with an indirect LC, as well as several non- Chaetodon species, sound production
includes both low and high frequency pulsed sounds with a stronger contribution of
the body of the swim bladder for auditory sensitivity (see Sects. 3 and 4 below).
The swim bladder of teleost fi shes is also quite important for the control of buoyancy, which makes the study of its adaptive evolution rather complex. The euphysoclistic swim bladder of chaetodontids (and other “advanced” teleosts) regulates its
air volume physiologically (by active secretion and passive resorption of gases).
Acoustic Communication in Butterfl yfi shes…
(Woods 2006 ; Woods et al. 2006 ; Webb et al. 2006 ). The swim bladder is bounded
dorsally by the vertebral column, laterally by the ribs, and ventrally by the peritoneum that lines the abdominal cavity. This confi guration limits the overall shape and
volume of the swim bladder as indicated by the obvious indentations in the volume
of air created by the ribs (Webb et al. 2006 ; Fig. 1c ). Neither extrinsic nor intrinsic
sonic muscles are found in association with the swim bladder, so the swim bladder
likely functions as a sound resonator, which is stimulated by the physical motion of
other adjacent sound production mechanisms (Sect. 3 below).
Variation in the morphology of the swim bladder may have implications for both
bioacoustic reception and sound production. The gross morphology of the swim
bladder varies among Chaetodon species (such variation within a genus is unusual
and thus notable), and is correlated with LC type (Direct, Indirect; with a few minor
exceptions; Webb 1998 ; Webb and Smith 2000 ; Smith et al. 2003 ; Fig. 4 ). Chaetodon
species with a Direct LC (e.g., C. auriga , C. octofasciatus ) have a swim bladder
with a distinct “kink” in its long axis, such that the anterior half of the swim bladder
and swim bladder horns is relatively horizontal, whereas the posterior half of the
swim bladder is more vertical in orientation. The thick tunica externa is composed
of multiple layers of collagen and is somewhat thicker dorsally than it is ventrally
(Woods 2006 ). The ventral surface of the swim bladder is covered by a thin peritoneum (lining of the abdominal cavity) that wraps tightly around the swim bladder’s
posterior end (a “free” swim bladder; Smith et al. 2003 ). The thickness of the lateral
wall of the swim bladder horns decreases quite dramatically near the medial opening in the supracleithrum (Woods 2006 ), which may allow pressure-induced movement of the tissue covering the opening resulting in movements of fl uids in the
canal. Sound production by Chaetodon species with a direct LC is so far quantifi ed
only in C. auriga (very low frequency pulse sounds; Sect. 3 ). In addition, the
enhanced auditory sensitivity of C. auriga appears to depend more on the swim
bladder horns rather than on the body of the swim bladder (Sect. 4 ).
In contrast, Chaetodon species with an Indirect LC (e.g., C. multicinctus , C.
unimaculatus , C. kleinii , C. ornatissimus ), and species in non- Chaetodon genera
( Forcipiger , Heniochus and Hemitaurichthys ) have a swim bladder that is more
smoothly contoured (lacking a “kink”). The tunica externa in these species is much
thinner overall (and translucent) when compared to that in species with a direct
LC. It is thinner dorsally than it is ventrally, but its thickness does not vary along the
length of the swim bladder or along the horns as in species with a Direct LC (Woods
2006 ). In contrast to species with Direct LC, a thick, opaque peritoneum covers the
ventral surface of the swim bladder and attaches laterally to the ribs (an “attached”
swim bladder; Smith et al. 2003 ; Webb et al. 2006 ). In several Chaetodon species
with an indirect LC, as well as several non- Chaetodon species, sound production
includes both low and high frequency pulsed sounds with a stronger contribution of
the body of the swim bladder for auditory sensitivity (see Sects. 3 and 4 below).
The swim bladder of teleost fi shes is also quite important for the control of buoyancy, which makes the study of its adaptive evolution rather complex. The euphysoclistic swim bladder of chaetodontids (and other “advanced” teleosts) regulates its
air volume physiologically (by active secretion and passive resorption of gases).
Acoustic Communication in Butterfl yfi shes…