man that only generate a few highly stereotyped and redundant call types
(Fig. 2.10). The tone-like hum has a prominent fundamental frequency and
several harmonics that are unchanging throughout the duration of the call,
which can last on the order of minutes to over one hour (Bass et al. 1999).
Increased hum duration, together with its temporal and spectral simplicity,
should increase detection (see McKibben and Bass 1998 for underwater
playbacks that examine the influence of duration on responsiveness).
Similarly, many teleosts, including midshipman (Fig. 2.10), generate long,
repetitive trains of stereotyped, pulse-like grunts or growls that should also
lead to increased detection. These signals, like those of other teleosts, are
also fairly broadband at frequencies above any predicted cutoff frequency.
Increased detection could be achieved by increasing the high-frequency
content of a signal and thereby shifting the signal’s spectrum farther away
from the cutoff frequency at any one depth. This can be accomplished by
moving to warmer water. The fundamental frequency of individual vocalizations increases with increasing temperature (e.g., Fine 1978; Torricelli et
al. 1990; Brantley and Bass 1994; Crawford et al. 1997). The mechanism
underlying this trait is an elegant example of how the abiotic environment
can directly affect acoustic signaling via its influence on the neural control
of sound production. As ambient water temperature increases, there is an
increase in the discharge frequency of a vocal pacemaker circuit in the brain
that controls the contraction rate of sonic muscles, which in turn establish
a sound’s fundamental frequency (Bass and Baker 1991). Although temperature affects the calls of other poikilothermic animals, including anuran
amphibians, the effect here is mainly on call-repetition rate (see Gerhardt
1983; Zelick et al. 1999).
A decrease in cutoff frequency could be attained by moving to deeper
water or by vocalizing at times of the day when water depth is greatest. For
example, midshipman fish build nests in the intertidal zone and exhibit a
peak in the occurrence of courtship and associated vocal behaviors after
sunset (Ibara et al. 1983; Brantley and Bass 1994; Bass et al. 1999) when the
high tides are greater in depth. Water depth, however, does not seem to
place any limitations on mate calling because individual males will generate hums in 80-liter aquaria (Ibara et al. 1983; Brantley and Bass 1994).
Might sound transmission and detection be influenced by the nest that
an individual chooses? For example, the composition of the nest’s substrate
material itself might affect the cutoff frequency. Intertidal species such as
midshipman build nests under shelters with rocky-gravel bottoms (Bass
1996). In comparison with a softer, mud-like substrate, a more rigid substrate should contribute to a decrease in the cutoff frequency (Rogers and
Cox 1988). These nests are also often clustered, which should enhance
detection of a nearby neighbor’s vocal signals (see Fig. 2.9 and Bass 1996).
Barimo and Fine (1998) mapped out the sound field for toadfish
(Opsanus tau) nesting in terra cotta drainage tiles on a flat, sandy substrate
at depths of 1–2 m.The sound field is bilaterally symmetrical around an indi52
A.H. Bass and C.W. Clark
(Fig. 2.10). The tone-like hum has a prominent fundamental frequency and
several harmonics that are unchanging throughout the duration of the call,
which can last on the order of minutes to over one hour (Bass et al. 1999).
Increased hum duration, together with its temporal and spectral simplicity,
should increase detection (see McKibben and Bass 1998 for underwater
playbacks that examine the influence of duration on responsiveness).
Similarly, many teleosts, including midshipman (Fig. 2.10), generate long,
repetitive trains of stereotyped, pulse-like grunts or growls that should also
lead to increased detection. These signals, like those of other teleosts, are
also fairly broadband at frequencies above any predicted cutoff frequency.
Increased detection could be achieved by increasing the high-frequency
content of a signal and thereby shifting the signal’s spectrum farther away
from the cutoff frequency at any one depth. This can be accomplished by
moving to warmer water. The fundamental frequency of individual vocalizations increases with increasing temperature (e.g., Fine 1978; Torricelli et
al. 1990; Brantley and Bass 1994; Crawford et al. 1997). The mechanism
underlying this trait is an elegant example of how the abiotic environment
can directly affect acoustic signaling via its influence on the neural control
of sound production. As ambient water temperature increases, there is an
increase in the discharge frequency of a vocal pacemaker circuit in the brain
that controls the contraction rate of sonic muscles, which in turn establish
a sound’s fundamental frequency (Bass and Baker 1991). Although temperature affects the calls of other poikilothermic animals, including anuran
amphibians, the effect here is mainly on call-repetition rate (see Gerhardt
1983; Zelick et al. 1999).
A decrease in cutoff frequency could be attained by moving to deeper
water or by vocalizing at times of the day when water depth is greatest. For
example, midshipman fish build nests in the intertidal zone and exhibit a
peak in the occurrence of courtship and associated vocal behaviors after
sunset (Ibara et al. 1983; Brantley and Bass 1994; Bass et al. 1999) when the
high tides are greater in depth. Water depth, however, does not seem to
place any limitations on mate calling because individual males will generate hums in 80-liter aquaria (Ibara et al. 1983; Brantley and Bass 1994).
Might sound transmission and detection be influenced by the nest that
an individual chooses? For example, the composition of the nest’s substrate
material itself might affect the cutoff frequency. Intertidal species such as
midshipman build nests under shelters with rocky-gravel bottoms (Bass
1996). In comparison with a softer, mud-like substrate, a more rigid substrate should contribute to a decrease in the cutoff frequency (Rogers and
Cox 1988). These nests are also often clustered, which should enhance
detection of a nearby neighbor’s vocal signals (see Fig. 2.9 and Bass 1996).
Barimo and Fine (1998) mapped out the sound field for toadfish
(Opsanus tau) nesting in terra cotta drainage tiles on a flat, sandy substrate
at depths of 1–2 m.The sound field is bilaterally symmetrical around an indi52
A.H. Bass and C.W. Clark