87
masking effects occur given their apparent low absolute hearing sensitivity (see
Sect. 3 ). Nonetheless, effective acoustic communication is degraded at large distances in a noisy reef environment and the signal to noise ratio is enhanced at the
short distances of separation found among individuals of most butterfl yfi sh species
(Tricas and Boyle 2015b ).
This analysis is founded on the interpretation of acoustic communication within
the butterfl yfi sh’s natural habitat. However, more studies of sensory ecology are
needed in which local ambient noise levels and frequency spectra are considered
across different time scales (diel, lunar, season, annual), among sub-habitats, and
with respect to natural acoustic signals and hearing capabilities of butterfl yfi shes in
order to determine the nature of the constraints on acoustic communication. For
example, higher signal-to-noise ratios at lower frequencies of <1–100 Hz are
expected to occur on leeward reefs, which normally experience low wind velocity
and wave conditions when compared to windward reefs, which are subject to stronger and continuous trade winds. Furthermore, recordings of ambient noise levels
made on reefs (e.g., Simpson et al. 2005 ; Radford et al. 2014 ; Tricas and Boyle
2015b ) have not yet distinguished between the hydrodynamic (surge/water turbulence) and sound pressure components of ambient sounds, which will also differ,
respectively, with habitat and depth. In addition, distinct spectral and intensity signatures are found in different coastal habitats, and it is suggested that these may
provide important navigational cues for larval reef fi shes (Kennedy et al. 2010 ;
Radford et al. 2014 ). However, it should be noted that the swim bladder horns of C.
ocellatus , which impart sound pressure sensitivity in adult Chaetodon , do not
develop until larvae have already moved into potential settlement areas. Thus, they
do not likely play a role in interpreting acoustic stimuil that may be inolved in fi nding suitable settlement sites (Webb et al. 2012 ).
7 Conclusions and Future Work
The study of the ecology and social behavior of butterfl yfi shes has provided an
exciting context for the discovery and interpretation of auditory anatomy, auditory
physiology, and the evolution of sound production and sensory systems. Some
important questions that should guide future research are detailed below.
1. Sound production and hearing, in addition to vision and chemoreception, are
important in the complex social behavior of butterfl yfi shes. The head bob acoustic
behavior appears to be a shared character of several species in the bannerfi sh and
Chaetodon clades, whereas the tail slap acoustic behavior appears to be a derived
character in Chaetodon . The occurrence of sound production and sound communication in butterfl yfi sh genera other than Chaetodon indicates that these capabilities evolved in the family prior to the evolutionary origin of Chaetodon and the
LC, which is a defi ning character of that genus. Furthermore, the evolution of
swim bladder horns and the laterophysic connection (LC) in Chaetodon was not
Acoustic Communication in Butterfl yfi shes…
masking effects occur given their apparent low absolute hearing sensitivity (see
Sect. 3 ). Nonetheless, effective acoustic communication is degraded at large distances in a noisy reef environment and the signal to noise ratio is enhanced at the
short distances of separation found among individuals of most butterfl yfi sh species
(Tricas and Boyle 2015b ).
This analysis is founded on the interpretation of acoustic communication within
the butterfl yfi sh’s natural habitat. However, more studies of sensory ecology are
needed in which local ambient noise levels and frequency spectra are considered
across different time scales (diel, lunar, season, annual), among sub-habitats, and
with respect to natural acoustic signals and hearing capabilities of butterfl yfi shes in
order to determine the nature of the constraints on acoustic communication. For
example, higher signal-to-noise ratios at lower frequencies of <1–100 Hz are
expected to occur on leeward reefs, which normally experience low wind velocity
and wave conditions when compared to windward reefs, which are subject to stronger and continuous trade winds. Furthermore, recordings of ambient noise levels
made on reefs (e.g., Simpson et al. 2005 ; Radford et al. 2014 ; Tricas and Boyle
2015b ) have not yet distinguished between the hydrodynamic (surge/water turbulence) and sound pressure components of ambient sounds, which will also differ,
respectively, with habitat and depth. In addition, distinct spectral and intensity signatures are found in different coastal habitats, and it is suggested that these may
provide important navigational cues for larval reef fi shes (Kennedy et al. 2010 ;
Radford et al. 2014 ). However, it should be noted that the swim bladder horns of C.
ocellatus , which impart sound pressure sensitivity in adult Chaetodon , do not
develop until larvae have already moved into potential settlement areas. Thus, they
do not likely play a role in interpreting acoustic stimuil that may be inolved in fi nding suitable settlement sites (Webb et al. 2012 ).
7 Conclusions and Future Work
The study of the ecology and social behavior of butterfl yfi shes has provided an
exciting context for the discovery and interpretation of auditory anatomy, auditory
physiology, and the evolution of sound production and sensory systems. Some
important questions that should guide future research are detailed below.
1. Sound production and hearing, in addition to vision and chemoreception, are
important in the complex social behavior of butterfl yfi shes. The head bob acoustic
behavior appears to be a shared character of several species in the bannerfi sh and
Chaetodon clades, whereas the tail slap acoustic behavior appears to be a derived
character in Chaetodon . The occurrence of sound production and sound communication in butterfl yfi sh genera other than Chaetodon indicates that these capabilities evolved in the family prior to the evolutionary origin of Chaetodon and the
LC, which is a defi ning character of that genus. Furthermore, the evolution of
swim bladder horns and the laterophysic connection (LC) in Chaetodon was not
Acoustic Communication in Butterfl yfi shes…