131
increase their activity and approach a speaker broadcasting male courtship signals.
Playback studies with cyprinids (Notropis sp.), sunfish (Lepomis sp.), Hawaiian
squirrelfish (Myripristus berndti), and bicolor damselfish (Eupomacentrus partitus)
showed greater attraction to the sounds of conspecifics than to those of heterospecifics (Delco 1960; Gerald 1971; Myrberg and Spires 1972; Popper et al. 1973). Winn
(1972) showed that reproductive female oyster toadfish (Opsanus tau) will exhibit
phonotaxis to the playback of the male’s “boatwhistle” signal. Similar to its Atlantic
relative, the plainfin midshipman fish (Porichthys notatus) is also known to exhibit
similar phonotaxis responses. Ibara et al. (1983) and McKibben and Bass (1998)
showed that gravid female midshipman (full of eggs) will exhibit robust phonotaxis
to the playback of pre-recorded advertisement calls or pure tones (80–115 Hz) that
were similar to the fundamental frequencies of natural advertisement calls or
“hums.” The frequency preferences based on female phonotaxis were found to be
linearly related to water temperature that increased approximately 5 Hz/°C and was
about 100 Hz at 16 °C (Brantley and Bass 1994; McKibben and Bass 1998).
McKibben and Bass (1998) used one-choice tests to determine call recognition and
two-choice tests to evaluate signal preferences based on differences in harmonics,
fundamental frequency, amplitude, frequency modulation, and beat stimuli. The
results from their study and another (McKibben and Bass 2001) are perhaps the best
and clearest evidence that fishes are able to locate sound sources in three- dimensional
space. Until recently it was unclear what sound cues and search strategies midshipman used to locate sound sources. For example, do female midshipman locate
sources by “climbing up” the intensity gradient (klinotaxis), or approach the source
using a strategy analogous to the “light compass reaction” (Fraenkel and Gunn
1961) where the local particle motion vectors play the role of the sun to which the
fish maintains a constant orientation angle to reach the source similar to Kalmijn’s
guided approach hypothesis (Kalmijn 1997), or do females already “know” where
the source is and have already determined the source location at the initial time of
release? These were just some of the questions that have persisted after the initial
observations of phonotaxis by female midshipman.
Recently Zeddies et al. (2010, 2012) performed new phonotaxis experiments
using the plainfin midshipman to investigate how these fish locate sound sources in
relatively simple and complex sound fields. The experiments were performed in the
same testing arena used previously by McKibben and Bass (1998, 2001). In the first
set of experiments, Zeddies et al. (2010) investigated how female midshipman
localized a sound source in the relatively simple geometry of a monopole sound
field. A US Navy J9 sound projector was used to generate a monopole sound field
in a large outdoor tank at the UC Bodega Marine Laboratory that allowed the
researchers to observe female phonotaxis behavior in a controlled environment
where the sound field could be easily measured. The projector was suspended from
a beam and positioned in the center of the tank where it broadcasted an acoustic
stimulus of a 90 Hz tone, which was similar to the fundamental frequency of the
male advertisement call. During the playback experiments, an opaque plastic tarp
was positioned in front, but not touching, the sound projector to remove any visual
cues that could potential affect the sound source localization behavior of midshipDirectional Hearing and Sound Source Localization in Fishes
increase their activity and approach a speaker broadcasting male courtship signals.
Playback studies with cyprinids (Notropis sp.), sunfish (Lepomis sp.), Hawaiian
squirrelfish (Myripristus berndti), and bicolor damselfish (Eupomacentrus partitus)
showed greater attraction to the sounds of conspecifics than to those of heterospecifics (Delco 1960; Gerald 1971; Myrberg and Spires 1972; Popper et al. 1973). Winn
(1972) showed that reproductive female oyster toadfish (Opsanus tau) will exhibit
phonotaxis to the playback of the male’s “boatwhistle” signal. Similar to its Atlantic
relative, the plainfin midshipman fish (Porichthys notatus) is also known to exhibit
similar phonotaxis responses. Ibara et al. (1983) and McKibben and Bass (1998)
showed that gravid female midshipman (full of eggs) will exhibit robust phonotaxis
to the playback of pre-recorded advertisement calls or pure tones (80–115 Hz) that
were similar to the fundamental frequencies of natural advertisement calls or
“hums.” The frequency preferences based on female phonotaxis were found to be
linearly related to water temperature that increased approximately 5 Hz/°C and was
about 100 Hz at 16 °C (Brantley and Bass 1994; McKibben and Bass 1998).
McKibben and Bass (1998) used one-choice tests to determine call recognition and
two-choice tests to evaluate signal preferences based on differences in harmonics,
fundamental frequency, amplitude, frequency modulation, and beat stimuli. The
results from their study and another (McKibben and Bass 2001) are perhaps the best
and clearest evidence that fishes are able to locate sound sources in three- dimensional
space. Until recently it was unclear what sound cues and search strategies midshipman used to locate sound sources. For example, do female midshipman locate
sources by “climbing up” the intensity gradient (klinotaxis), or approach the source
using a strategy analogous to the “light compass reaction” (Fraenkel and Gunn
1961) where the local particle motion vectors play the role of the sun to which the
fish maintains a constant orientation angle to reach the source similar to Kalmijn’s
guided approach hypothesis (Kalmijn 1997), or do females already “know” where
the source is and have already determined the source location at the initial time of
release? These were just some of the questions that have persisted after the initial
observations of phonotaxis by female midshipman.
Recently Zeddies et al. (2010, 2012) performed new phonotaxis experiments
using the plainfin midshipman to investigate how these fish locate sound sources in
relatively simple and complex sound fields. The experiments were performed in the
same testing arena used previously by McKibben and Bass (1998, 2001). In the first
set of experiments, Zeddies et al. (2010) investigated how female midshipman
localized a sound source in the relatively simple geometry of a monopole sound
field. A US Navy J9 sound projector was used to generate a monopole sound field
in a large outdoor tank at the UC Bodega Marine Laboratory that allowed the
researchers to observe female phonotaxis behavior in a controlled environment
where the sound field could be easily measured. The projector was suspended from
a beam and positioned in the center of the tank where it broadcasted an acoustic
stimulus of a 90 Hz tone, which was similar to the fundamental frequency of the
male advertisement call. During the playback experiments, an opaque plastic tarp
was positioned in front, but not touching, the sound projector to remove any visual
cues that could potential affect the sound source localization behavior of midshipDirectional Hearing and Sound Source Localization in Fishes