76
hearing sensitivity in Chaetodon species. Butterfl yfi shes are diurnally active in the
clear waters of coral reefs and exhibit numerous forms of complex social and mating behaviors that include monogamous pairing, haremic mating systems, solitary
behavior, and aggregation or schooling (Reese 1975 ; Hourigan 1989 ; Yabuta and
Berumen 2014 ). A recent fi eld study shows that while visual signals are used for
recognition of conspecifi cs and other behaviors in these colorful fi shes (see Sect. 1 ),
chemical cues are also required for the discrimination of mates from non-mates
(Boyle and Tricas 2014 ). In this section, we fi rst review the basic features of underwater acoustic fi elds and how they are likely encoded by the fi sh auditory and lateral
line systems. We then interpret in more detail how the butterfl yfi sh ear and lateral
line systems likely encode their biologically relevant acoustic signals that they produce during social interactions.
4.1 The Acoustic Field: Hydrodynamic Particle Motion
and Sound Pressure Stimuli
The acoustic fi eld of an underwater sound includes a hydrodynamic fl ow component
in close proximity to the source that can accelerate the body of a nearby receiver and
directly stimulate the inner ear (Kalmijn 1988 ; Braun and Grande 2008 ). During the
Hydrodynamic Tail Slap
Likelihood
Parsimony
C. ornatissimus
C. auriga
C. multicinctus
C. unimaculatus
C. kleinii
F. flavissimus
F. longirostris
H. polylepis
Hen. chrysostomus
Head Bob Sound
Likelihood
Parsimony
a
b
C. ornatissimus
C. auriga
C. multicinctus
C. unimaculatus
C. kleinii
F. flavissimus
F. longirostris
H. polylepis
Hen. chrysostomus
Fig. 8 Ancestral state reconstruction of two acoustic behaviors used during social interactions in
butterfl yfi shes. ( a ) The head bob acoustic behavior occurs in both Chaetodon and Forcipiger with
an equivocal likelihood for it as the ancestral state ( left ), and the possible independent evolution
among clades in the parsimony model ( right ). ( b ) The tail slap behavior is so far observed during
social interactions only by Chaetodon species and produces a very low frequency acoustic stimulus that is directed towards the receiver fi sh. It is not yet documented in the bannerfi sh clade and
both the likelihood ( left ) and parsimony ( right ) models are equivocal on the presence of this trait
in the common ancestor. The darkened portion of the circles indicates the probability that the trait
is present at each node. C Chaetodon , F. Forcipiger , H. Hemitaurichthys , Hen. Heniochus . From
Tricas and Boyle ( 2015a )
T.C. Tricas and J.F. Webb
hearing sensitivity in Chaetodon species. Butterfl yfi shes are diurnally active in the
clear waters of coral reefs and exhibit numerous forms of complex social and mating behaviors that include monogamous pairing, haremic mating systems, solitary
behavior, and aggregation or schooling (Reese 1975 ; Hourigan 1989 ; Yabuta and
Berumen 2014 ). A recent fi eld study shows that while visual signals are used for
recognition of conspecifi cs and other behaviors in these colorful fi shes (see Sect. 1 ),
chemical cues are also required for the discrimination of mates from non-mates
(Boyle and Tricas 2014 ). In this section, we fi rst review the basic features of underwater acoustic fi elds and how they are likely encoded by the fi sh auditory and lateral
line systems. We then interpret in more detail how the butterfl yfi sh ear and lateral
line systems likely encode their biologically relevant acoustic signals that they produce during social interactions.
4.1 The Acoustic Field: Hydrodynamic Particle Motion
and Sound Pressure Stimuli
The acoustic fi eld of an underwater sound includes a hydrodynamic fl ow component
in close proximity to the source that can accelerate the body of a nearby receiver and
directly stimulate the inner ear (Kalmijn 1988 ; Braun and Grande 2008 ). During the
Hydrodynamic Tail Slap
Likelihood
Parsimony
C. ornatissimus
C. auriga
C. multicinctus
C. unimaculatus
C. kleinii
F. flavissimus
F. longirostris
H. polylepis
Hen. chrysostomus
Head Bob Sound
Likelihood
Parsimony
a
b
C. ornatissimus
C. auriga
C. multicinctus
C. unimaculatus
C. kleinii
F. flavissimus
F. longirostris
H. polylepis
Hen. chrysostomus
Fig. 8 Ancestral state reconstruction of two acoustic behaviors used during social interactions in
butterfl yfi shes. ( a ) The head bob acoustic behavior occurs in both Chaetodon and Forcipiger with
an equivocal likelihood for it as the ancestral state ( left ), and the possible independent evolution
among clades in the parsimony model ( right ). ( b ) The tail slap behavior is so far observed during
social interactions only by Chaetodon species and produces a very low frequency acoustic stimulus that is directed towards the receiver fi sh. It is not yet documented in the bannerfi sh clade and
both the likelihood ( left ) and parsimony ( right ) models are equivocal on the presence of this trait
in the common ancestor. The darkened portion of the circles indicates the probability that the trait
is present at each node. C Chaetodon , F. Forcipiger , H. Hemitaurichthys , Hen. Heniochus . From
Tricas and Boyle ( 2015a )
T.C. Tricas and J.F. Webb