112
than courtship sounds (Torricelli et al. 1990 ). By contrast, “purr” and “knock” train
durations of Etheostoma oophylax and Cottus paulus , respectively, were longer in
courtship contexts than agonistic contexts ( E. oophylax : 55 ms longer, Speares and
Johnston 2011 ; C. paulus : 200 ms longer, Kierl and Johnston 2010 ).
Dominant frequencies of Padogobius bonelli courtship sounds were higher than
aggressive sounds, after controlling for effects of water temperature (Torricelli et al.
1990 ), whereas opposite associations have been found for darters. Dominant frequencies of Etheostoma nigripinne drums and knocks were lower in courtship contexts than aggressive contexts (Johnston and Johnson 2000 ). Similarly, the
Etheostoma oophylax purr fundamental frequency was lower in courtship relative to
aggressive contexts (38 vs. 96 Hz, Speares and Johnston 2011 ). Despite differences
in the direction of acoustic parameter variation across species, these fi ndings indicate that males modify acoustic output based on the social context. Male evaluation
of the social context in Padogobius bonelli is at least partially mediated by chemical
cues, where female odour cues are necessary to elicit sounds in response to playbacks of male conspecifi c sounds (Lugli et al. 2004 ). Chemical signals stimulating
courtship have been identifi ed in Bathygobius soporator (Tavolga 1956 ).
6.3 Species Identity
For related species in sympatry, determining species identity can be an important
discrimination task in the reproductive context. Species identity could be encoded by
acoustic signals (Myrberg et al. 1978 ; Spanier 1979 ; Crawford et al. 1997 ; Lobel
1998 ). Selected studies of gobies and sculpins have supported fi ndings from other
fi shes (i.e., Centrachidae, Mormyridae, Pomacentridae, and Cichlidae) (Kihslinger
and Klimley 2002 ; Amorim et al. 2008 ) that pulse rate is a reliable species identifi er.
Sympatric sand gobies Pomatoschistus minutus and Pomatoschistus pictus , and sculpins Cottus perifretum and Cottus rhenanus differ in pulse repetition rate (Pedroso
et al. 2013 ; Colleye et al. 2013 ). Both of these studies also found dominant frequency
to effectively distinguish the sympatric species. The link between pulse dominant
frequency and body size in sculpins makes this a poor species identity attribute,
whereas it could be a reliable indicator in sand gobies, since there are no such body
size-dominant frequency relationships in these species (Pedroso et al. 2013 ).
7 Future Directions
7.1 How Do Acoustic Signals Modulate Spawning Physiology?
The observation that certain sound types are restricted to when a female has entered
the nest (e.g., Pomatoschistus and Knipowitschia , Lugli et al. 1997 ), the low sound
intensity of many species, and observations of escalated sound output as spawning
draws near (Lugli et al. 1997 ) indicate that acoustic signals may not be selected
J.N. Zeyl et al.
than courtship sounds (Torricelli et al. 1990 ). By contrast, “purr” and “knock” train
durations of Etheostoma oophylax and Cottus paulus , respectively, were longer in
courtship contexts than agonistic contexts ( E. oophylax : 55 ms longer, Speares and
Johnston 2011 ; C. paulus : 200 ms longer, Kierl and Johnston 2010 ).
Dominant frequencies of Padogobius bonelli courtship sounds were higher than
aggressive sounds, after controlling for effects of water temperature (Torricelli et al.
1990 ), whereas opposite associations have been found for darters. Dominant frequencies of Etheostoma nigripinne drums and knocks were lower in courtship contexts than aggressive contexts (Johnston and Johnson 2000 ). Similarly, the
Etheostoma oophylax purr fundamental frequency was lower in courtship relative to
aggressive contexts (38 vs. 96 Hz, Speares and Johnston 2011 ). Despite differences
in the direction of acoustic parameter variation across species, these fi ndings indicate that males modify acoustic output based on the social context. Male evaluation
of the social context in Padogobius bonelli is at least partially mediated by chemical
cues, where female odour cues are necessary to elicit sounds in response to playbacks of male conspecifi c sounds (Lugli et al. 2004 ). Chemical signals stimulating
courtship have been identifi ed in Bathygobius soporator (Tavolga 1956 ).
6.3 Species Identity
For related species in sympatry, determining species identity can be an important
discrimination task in the reproductive context. Species identity could be encoded by
acoustic signals (Myrberg et al. 1978 ; Spanier 1979 ; Crawford et al. 1997 ; Lobel
1998 ). Selected studies of gobies and sculpins have supported fi ndings from other
fi shes (i.e., Centrachidae, Mormyridae, Pomacentridae, and Cichlidae) (Kihslinger
and Klimley 2002 ; Amorim et al. 2008 ) that pulse rate is a reliable species identifi er.
Sympatric sand gobies Pomatoschistus minutus and Pomatoschistus pictus , and sculpins Cottus perifretum and Cottus rhenanus differ in pulse repetition rate (Pedroso
et al. 2013 ; Colleye et al. 2013 ). Both of these studies also found dominant frequency
to effectively distinguish the sympatric species. The link between pulse dominant
frequency and body size in sculpins makes this a poor species identity attribute,
whereas it could be a reliable indicator in sand gobies, since there are no such body
size-dominant frequency relationships in these species (Pedroso et al. 2013 ).
7 Future Directions
7.1 How Do Acoustic Signals Modulate Spawning Physiology?
The observation that certain sound types are restricted to when a female has entered
the nest (e.g., Pomatoschistus and Knipowitschia , Lugli et al. 1997 ), the low sound
intensity of many species, and observations of escalated sound output as spawning
draws near (Lugli et al. 1997 ) indicate that acoustic signals may not be selected
J.N. Zeyl et al.