78
about 70–85 dB re: 1 μm s
−2 (Fig. 9b ), which is similar to that reported for a marine
damselfi sh ( Chromis ) and goby ( Gobius ) that lack auditory specializations for
sound pressure sensitivity (Wysocki et al. 2009 ).
Comparison of butterfl yfi sh audiograms also shows evidence for sensitivity to
sound pressure and the resultant enhanced hearing capabilities in Chaetodon . The
maximum response frequency of 1000 Hz for some F. fl avissimus (which lacks
swim bladder horns) is considerably less than the 1700–2000 Hz maximum observed
for Chaetodon species (which have swim bladder horns and an LC, Fig. 9 ). An
extended upper frequency range of hearing is common for pressure sensitive fi shes
(see Ladich and Fay 2013 ). Recent comparative AEP experiments on cichlid genera
show that species with anterior swim bladder horns have improved auditory sensitivities of 20–40 dB (SPLs) at frequencies of 0.5 to 1 kHz (Schulz-Mirbach et al.
2012 ), which is higher than the improvement in hearing sensitivity for Chaetodon
(10–15 dB) compared to Forcipger. In addition, the frequency of lowest hearing
thresholds (best frequency) in species sensitive to sound pressure is predicted to be
greater than 100–200 Hz (Ladich and Fay 2013 ) and this is best seen at 600 Hz for
C. multicinctus (Figs. 9 and 10c ). Experimental displacement of gas from the swim
bladder horns (by the injection of gel) in both C. multicinctus (LC variant Ind1) and
C. auriga (LC variant Dir1) decreased auditory sensitivity (increased thresholds) in
the low pass 200–600 Hz frequency range and variably among species at higher
frequencies (Fig. 10c, d ). Removal of gas from the swim bladder horns and body in
Chaetodon species increases their hearing thresholds much closer to that of
Foripiger (Fig. 10b–d ). Combined, these fi ndings support the hypothesis that all
butterfl yfi shes are primarily sensitive to hydrodynamic particle acceleration and
that hearing sensitivity and frequency range are enhanced by the transduction of
sound pressure stimuli mediated by the swim bladder horns in Chaetodon species
with either Direct or Indirect LC’s.
Enhanced frequency sensitivity in Chaetodon may facilitate acoustic communication. The frequency band of best sensitivity to sound pressure stimuli at 200–600 Hz
overlaps the frequency spectrum of the body motion pulse in C. multicinctus and C.
ornatissiumus , the head bob-jaw protrusion pulse of C. unimaculatus , and the jaw
protrusion pulse sound of C. kleinii (Fig. 6 , Table 2 , Tricas and Boyle 2015b ). This
match provides evidence that the swim bladder horns can enhance the perception of
biologically relevant acoustic signals used in social interactions. However, enhanced
Fig. 9 (continued)measured as total sound pressure level (SPL) are similar among Chaetodon species with lower thresholds and an extended response range to 1700 Hz for all species and to
2000 Hz for C. ornatissimus . ( b ) Thresholds measured as particle acceleration level (PAL) show
similar curve shapes to SPL audiograms. The accelerometer was not calibrated at 2000 Hz, thus
that data point is lacking for C. ornatissimus. N = sample size of fi sh tested at each frequency.
Fractions indicate the proportion of tested fi sh that showed a response. Audiograms are means and
SE for thresholds for all fi sh tested at a given frequency in that study in order to increase sample
size, increase frequency resolution and to reduce variation for overlaying of the comparative
audiogram plots. From Tricas and Boyle ( 2015b )
T.C. Tricas and J.F. Webb
about 70–85 dB re: 1 μm s
−2 (Fig. 9b ), which is similar to that reported for a marine
damselfi sh ( Chromis ) and goby ( Gobius ) that lack auditory specializations for
sound pressure sensitivity (Wysocki et al. 2009 ).
Comparison of butterfl yfi sh audiograms also shows evidence for sensitivity to
sound pressure and the resultant enhanced hearing capabilities in Chaetodon . The
maximum response frequency of 1000 Hz for some F. fl avissimus (which lacks
swim bladder horns) is considerably less than the 1700–2000 Hz maximum observed
for Chaetodon species (which have swim bladder horns and an LC, Fig. 9 ). An
extended upper frequency range of hearing is common for pressure sensitive fi shes
(see Ladich and Fay 2013 ). Recent comparative AEP experiments on cichlid genera
show that species with anterior swim bladder horns have improved auditory sensitivities of 20–40 dB (SPLs) at frequencies of 0.5 to 1 kHz (Schulz-Mirbach et al.
2012 ), which is higher than the improvement in hearing sensitivity for Chaetodon
(10–15 dB) compared to Forcipger. In addition, the frequency of lowest hearing
thresholds (best frequency) in species sensitive to sound pressure is predicted to be
greater than 100–200 Hz (Ladich and Fay 2013 ) and this is best seen at 600 Hz for
C. multicinctus (Figs. 9 and 10c ). Experimental displacement of gas from the swim
bladder horns (by the injection of gel) in both C. multicinctus (LC variant Ind1) and
C. auriga (LC variant Dir1) decreased auditory sensitivity (increased thresholds) in
the low pass 200–600 Hz frequency range and variably among species at higher
frequencies (Fig. 10c, d ). Removal of gas from the swim bladder horns and body in
Chaetodon species increases their hearing thresholds much closer to that of
Foripiger (Fig. 10b–d ). Combined, these fi ndings support the hypothesis that all
butterfl yfi shes are primarily sensitive to hydrodynamic particle acceleration and
that hearing sensitivity and frequency range are enhanced by the transduction of
sound pressure stimuli mediated by the swim bladder horns in Chaetodon species
with either Direct or Indirect LC’s.
Enhanced frequency sensitivity in Chaetodon may facilitate acoustic communication. The frequency band of best sensitivity to sound pressure stimuli at 200–600 Hz
overlaps the frequency spectrum of the body motion pulse in C. multicinctus and C.
ornatissiumus , the head bob-jaw protrusion pulse of C. unimaculatus , and the jaw
protrusion pulse sound of C. kleinii (Fig. 6 , Table 2 , Tricas and Boyle 2015b ). This
match provides evidence that the swim bladder horns can enhance the perception of
biologically relevant acoustic signals used in social interactions. However, enhanced
Fig. 9 (continued)measured as total sound pressure level (SPL) are similar among Chaetodon species with lower thresholds and an extended response range to 1700 Hz for all species and to
2000 Hz for C. ornatissimus . ( b ) Thresholds measured as particle acceleration level (PAL) show
similar curve shapes to SPL audiograms. The accelerometer was not calibrated at 2000 Hz, thus
that data point is lacking for C. ornatissimus. N = sample size of fi sh tested at each frequency.
Fractions indicate the proportion of tested fi sh that showed a response. Audiograms are means and
SE for thresholds for all fi sh tested at a given frequency in that study in order to increase sample
size, increase frequency resolution and to reduce variation for overlaying of the comparative
audiogram plots. From Tricas and Boyle ( 2015b )
T.C. Tricas and J.F. Webb