99
2 Diversity of Sound Types with Phylogenetic
Considerations
The acoustic repertoires of darters, gobies, and sculpins are constructed from pulsed
units with dominant frequencies below 200 Hz (Fig. 1 , Tables 1 and 3 ). The variety
of sound structures that have been classifi ed are generated from variation in the
temporal spacing of pulse repetition. At one end of the continuum, pulses are produced with long, irregular inter-pulse intervals where each “knock” or “pulse” is
clearly distinguishable to the human ear (e.g., Cottus carolinae ). Pulses may also be
strung closer together into coherent pulse train bursts with regular repetition rates
(i.e., “drumming”, “purrs”, or “grunt” sounds) (e.g., Etheostoma corona ). In the
repertoires of some sculpins, some gobies, and all of the currently tested darters,
pulses may resolve to tonal structures at a high repetition rate. For the purposes of
comparison, we classify the fi rst two sound types (single pulses and structured pulse
trains) as “pulsatile” and the third as “tonal”. In gobies, sounds that possess both
tonal and drumming components within the same burst have been classifi ed as
“complex” (Lugli et al. 1997 ). Darters exhibit similar continuities between pulse
trains and tonal sounds (e.g., Fig. 1 a, b).
2.1 Darters
All of the soniferous darters tested to date have repertoires that include both pulsatile and tonal sounds, which have been classifi ed into three sound structures: isolated pulsatile “knocks”, pulse train “purrs”, and harmonic “drums” (Fig. 1a, b ).
Drums typically exhibit a rise and fall of the frequency contour structure (Johnston
and Johnson 2000 ; Speares and Johnston 2011 ), although additional infl ection
points are possible. A particularly high degree of frequency modulation is evident
in Etheostoma fl abellare (Fig. 1a ) (previously unpublished data). Darters can exhibit
considerable variation in the drum duration and degree of frequency modulation
within the same individuals.
Despite a signifi cant survey across darter phylogeny, sound production has only
been found in the Catonotus clade, suggesting that it may be a derived condition in
this group. Within Catonotus , sound production appears to be absent in the barcheek
group ( Etheostoma smithi and Etheostoma virgatum , CEJ unpublished data).
Outside Catonotus , a number of darters have been tested and found to be silent during spawning. These species can be distinguished from Catonotus in utilizing eggburying and egg-attaching spawning modes, where eggs are abandoned after
spawning: Percina palmaris , Etheostoma luteovictum (egg-buriers), Etheostoma
parvipinne , Etheostoma prolarie , Etheostoma blennius , Etheostoma simoterum ,
and Etheostoma duryi , (egg attachers, CEJ unpublished data) (Page 1985 ). Such an
association between territoriality and sound production is interesting given that
communication commonly occurs in territorial contexts in other taxa (Bradbury and
Convergent Aspects of Acoustic Communication in Darters, Sculpins, and Gobies
2 Diversity of Sound Types with Phylogenetic
Considerations
The acoustic repertoires of darters, gobies, and sculpins are constructed from pulsed
units with dominant frequencies below 200 Hz (Fig. 1 , Tables 1 and 3 ). The variety
of sound structures that have been classifi ed are generated from variation in the
temporal spacing of pulse repetition. At one end of the continuum, pulses are produced with long, irregular inter-pulse intervals where each “knock” or “pulse” is
clearly distinguishable to the human ear (e.g., Cottus carolinae ). Pulses may also be
strung closer together into coherent pulse train bursts with regular repetition rates
(i.e., “drumming”, “purrs”, or “grunt” sounds) (e.g., Etheostoma corona ). In the
repertoires of some sculpins, some gobies, and all of the currently tested darters,
pulses may resolve to tonal structures at a high repetition rate. For the purposes of
comparison, we classify the fi rst two sound types (single pulses and structured pulse
trains) as “pulsatile” and the third as “tonal”. In gobies, sounds that possess both
tonal and drumming components within the same burst have been classifi ed as
“complex” (Lugli et al. 1997 ). Darters exhibit similar continuities between pulse
trains and tonal sounds (e.g., Fig. 1 a, b).
2.1 Darters
All of the soniferous darters tested to date have repertoires that include both pulsatile and tonal sounds, which have been classifi ed into three sound structures: isolated pulsatile “knocks”, pulse train “purrs”, and harmonic “drums” (Fig. 1a, b ).
Drums typically exhibit a rise and fall of the frequency contour structure (Johnston
and Johnson 2000 ; Speares and Johnston 2011 ), although additional infl ection
points are possible. A particularly high degree of frequency modulation is evident
in Etheostoma fl abellare (Fig. 1a ) (previously unpublished data). Darters can exhibit
considerable variation in the drum duration and degree of frequency modulation
within the same individuals.
Despite a signifi cant survey across darter phylogeny, sound production has only
been found in the Catonotus clade, suggesting that it may be a derived condition in
this group. Within Catonotus , sound production appears to be absent in the barcheek
group ( Etheostoma smithi and Etheostoma virgatum , CEJ unpublished data).
Outside Catonotus , a number of darters have been tested and found to be silent during spawning. These species can be distinguished from Catonotus in utilizing eggburying and egg-attaching spawning modes, where eggs are abandoned after
spawning: Percina palmaris , Etheostoma luteovictum (egg-buriers), Etheostoma
parvipinne , Etheostoma prolarie , Etheostoma blennius , Etheostoma simoterum ,
and Etheostoma duryi , (egg attachers, CEJ unpublished data) (Page 1985 ). Such an
association between territoriality and sound production is interesting given that
communication commonly occurs in territorial contexts in other taxa (Bradbury and
Convergent Aspects of Acoustic Communication in Darters, Sculpins, and Gobies