285
propagating pressure wave (Popper and Fay 1993 ). The lateral line is sensitive to
hydrodynamic fl ow within short distances from the source (nearfi eld), but is relatively insensitive to pressure (farfi eld) (Montgomery et al. 1995 ; Webb et al. 2008 ).
Therefore, it is likely that the acoustic stimulation of the lateral line of teleosts will
transpire in close proximity to the source. The near fi eld dominates the acoustic
fi eld up to a distance of λ /2 π from the source (Bass and Clarke 2002 ), and should
extend at least 1–3 m from the nests based on the fundamental frequencies of the
boatwhistle, which would place the female fi sh well within the range of the acoustic
fi eld that would provide lateral line stimulation. The utricle may be able to detect
vocalizations outside of the near fi eld, providing the toadfi sh with both a long and
short range acoustic detection system.
4.2 Self-generated Movement
Body movements, including normal ventilation, stimulate both the utricle and the
anterior lateral line, and it is unclear the effects this has on sound sensitivity. While
rhythmic movements may be fi ltered in higher order processing centers (Montgomery
and Bodznick 1994 ), the ability to hear and/or fi nd the sound source may be compromised by nonrhythmic or spontaneous movement. During predation strikes, the
anterior lateral line was saturated in toadfi sh and unlikely to be able to integrate
additional prey information (Palmer et al. 2005 ). However, the toadfi sh is an ambush
predator that launches ballistic strikes, and its large mouth provides suffi cient margin for error that sensory feedback during the strike is probably unnecessary.
Male toadfi sh also remain relatively stationary during advertisement calling and
alternate calls to avoid overlap. However, they remain sensitive to conspecifi c signals which allows them to generate disruptive grunts during competitors’ boatwhistles (Mensinger 2014 ). However, there is no evidence that they can detect these
grunts, as the caller’s auditory system is either saturated by boatwhistle generation
or efferently modulated to avoid potentially damaging sound production. Thus, their
quiescent nature during acoustical advertisement generates little movement and
allows toadfi sh to maintain hearing sensitivity during inter call intervals.
The situation is more complicated for mobile females as they need to localize the
males and swim to the nest. Swimming can cause maximal excitation of utricle and
lateral line afferents and degrade the ability to pin point sound sources during these
forays. Although in situ observations of female fi sh approaching males from a distance are complicated by the poor environmental visibility, one would predict that if
the utricle is important in localizing sound, that the females may need to alternate
swimming with stationary pauses to assist in locating the sound. This intermittent
swimming strategy which has been observed in captivity may allow the fi sh to sample the acoustic fi eld during stops using both the saccule and utricle and help localize the sound source.
However, not all movement may degrade acoustic sensitivity. The superfi cial
neuromasts in the toadfi sh are surrounded by paired fi nger like projections and
Multimodal Sensory Input in the Utricle and Lateral Line of the Toadfi sh, Opsanus…
propagating pressure wave (Popper and Fay 1993 ). The lateral line is sensitive to
hydrodynamic fl ow within short distances from the source (nearfi eld), but is relatively insensitive to pressure (farfi eld) (Montgomery et al. 1995 ; Webb et al. 2008 ).
Therefore, it is likely that the acoustic stimulation of the lateral line of teleosts will
transpire in close proximity to the source. The near fi eld dominates the acoustic
fi eld up to a distance of λ /2 π from the source (Bass and Clarke 2002 ), and should
extend at least 1–3 m from the nests based on the fundamental frequencies of the
boatwhistle, which would place the female fi sh well within the range of the acoustic
fi eld that would provide lateral line stimulation. The utricle may be able to detect
vocalizations outside of the near fi eld, providing the toadfi sh with both a long and
short range acoustic detection system.
4.2 Self-generated Movement
Body movements, including normal ventilation, stimulate both the utricle and the
anterior lateral line, and it is unclear the effects this has on sound sensitivity. While
rhythmic movements may be fi ltered in higher order processing centers (Montgomery
and Bodznick 1994 ), the ability to hear and/or fi nd the sound source may be compromised by nonrhythmic or spontaneous movement. During predation strikes, the
anterior lateral line was saturated in toadfi sh and unlikely to be able to integrate
additional prey information (Palmer et al. 2005 ). However, the toadfi sh is an ambush
predator that launches ballistic strikes, and its large mouth provides suffi cient margin for error that sensory feedback during the strike is probably unnecessary.
Male toadfi sh also remain relatively stationary during advertisement calling and
alternate calls to avoid overlap. However, they remain sensitive to conspecifi c signals which allows them to generate disruptive grunts during competitors’ boatwhistles (Mensinger 2014 ). However, there is no evidence that they can detect these
grunts, as the caller’s auditory system is either saturated by boatwhistle generation
or efferently modulated to avoid potentially damaging sound production. Thus, their
quiescent nature during acoustical advertisement generates little movement and
allows toadfi sh to maintain hearing sensitivity during inter call intervals.
The situation is more complicated for mobile females as they need to localize the
males and swim to the nest. Swimming can cause maximal excitation of utricle and
lateral line afferents and degrade the ability to pin point sound sources during these
forays. Although in situ observations of female fi sh approaching males from a distance are complicated by the poor environmental visibility, one would predict that if
the utricle is important in localizing sound, that the females may need to alternate
swimming with stationary pauses to assist in locating the sound. This intermittent
swimming strategy which has been observed in captivity may allow the fi sh to sample the acoustic fi eld during stops using both the saccule and utricle and help localize the sound source.
However, not all movement may degrade acoustic sensitivity. The superfi cial
neuromasts in the toadfi sh are surrounded by paired fi nger like projections and
Multimodal Sensory Input in the Utricle and Lateral Line of the Toadfi sh, Opsanus…