192
multimodal mechanosensory response driven by both the ear and the lateral line
system. With this in mind, it is interesting to re-examine the body of literature of
cavefi sh mechanosensation. Most of our knowledge of cavefi sh lateral line systems
comes from studies of the Mexican cavefi sh Astyanax mexicanus , and this species
has made important contributions to understanding lateral line systems in general
(Montgomery et al. 2001 ). The cave forms of Astyanax not only have many more
neuromasts than their surface counterparts (Montgomery et al. 2001 ; Windsor et al.
2008 ; Yoshizawa et al. 2010 ) but also have enhanced behavioral sensitivity in feeding and navigation tasks (Sharma et al. 2009 ; Yoshizawa et al. 2010 ). Astyanax has
also evolved a form of active sensing in which they use a kick and glide swimming
style to generate a relatively stable, dipole-like fl ow signal during the glide phase of
the swimming cycle (Sharma et al. 2009 ; Patton et al. 2010 ). With this strategy
Astyanax use the distortions of nearby obstacles in the self-generated fl ow fi eld and
spend more time gliding when investigating a new object (Patton et al. 2010 ). Cave
amblyopsid species, the second most studied cavefi shes, also have more superfi cial
neuromasts that are larger with longer cupulae that their surface relatives, which
allow the detection of moving prey at a greater distance compared their surface relatives (Poulson 1963 ; Niemiller and Poulson 2010 ). Thus, the mechanosensory neuromasts have also undergone adaptive evolution, and, in conjunction with auditory
hair cells, allow enhanced non-visual detection of prey, predators, and obstacles in
their natural environment.
3 Infl uence of Arthur Popper and Richard Fay on Cavefi sh
Bioacoustics
While Arthur Popper obviously infl uenced this specifi c research topic by being the
fi rst to study hearing in cavefi sh (Popper 1970 ), the infl uence of both Popper and
Fay goes well beyond any individual research papers. The entire question of for
what, precisely, fi sh are using their sense of hearing (i.e., what fi sh are listening to)
remains largely unsolved, and Popper and Fay have repeatedly pushed the fi eld to
properly address this question (Popper and Fay 1973 , 1993 , 1997 ; Fay and Popper
2012 ). Their hypothesis of the ear evolving in response to “auditory scene analysis,” while largely untested, was a central reason for us to test the acoustic soundscape of the cave and surface environments in our work and formed the
underpinnings of much of what we were trying to assess. In addition, their longstanding interest in the evolution of fi sh hearing greatly infl uenced all three of us
to use the cave- and surface-dwelling species as a natural experiment to test
hypotheses fi rst laid out in the seminal papers of these two senior bioacousticians
(Fay and Popper 2012 ). Both have also served a personal mentoring role for two of
the authors of this current work, as they have done for the vast majority of researchers in this fi eld.
D. Soares et al.
multimodal mechanosensory response driven by both the ear and the lateral line
system. With this in mind, it is interesting to re-examine the body of literature of
cavefi sh mechanosensation. Most of our knowledge of cavefi sh lateral line systems
comes from studies of the Mexican cavefi sh Astyanax mexicanus , and this species
has made important contributions to understanding lateral line systems in general
(Montgomery et al. 2001 ). The cave forms of Astyanax not only have many more
neuromasts than their surface counterparts (Montgomery et al. 2001 ; Windsor et al.
2008 ; Yoshizawa et al. 2010 ) but also have enhanced behavioral sensitivity in feeding and navigation tasks (Sharma et al. 2009 ; Yoshizawa et al. 2010 ). Astyanax has
also evolved a form of active sensing in which they use a kick and glide swimming
style to generate a relatively stable, dipole-like fl ow signal during the glide phase of
the swimming cycle (Sharma et al. 2009 ; Patton et al. 2010 ). With this strategy
Astyanax use the distortions of nearby obstacles in the self-generated fl ow fi eld and
spend more time gliding when investigating a new object (Patton et al. 2010 ). Cave
amblyopsid species, the second most studied cavefi shes, also have more superfi cial
neuromasts that are larger with longer cupulae that their surface relatives, which
allow the detection of moving prey at a greater distance compared their surface relatives (Poulson 1963 ; Niemiller and Poulson 2010 ). Thus, the mechanosensory neuromasts have also undergone adaptive evolution, and, in conjunction with auditory
hair cells, allow enhanced non-visual detection of prey, predators, and obstacles in
their natural environment.
3 Infl uence of Arthur Popper and Richard Fay on Cavefi sh
Bioacoustics
While Arthur Popper obviously infl uenced this specifi c research topic by being the
fi rst to study hearing in cavefi sh (Popper 1970 ), the infl uence of both Popper and
Fay goes well beyond any individual research papers. The entire question of for
what, precisely, fi sh are using their sense of hearing (i.e., what fi sh are listening to)
remains largely unsolved, and Popper and Fay have repeatedly pushed the fi eld to
properly address this question (Popper and Fay 1973 , 1993 , 1997 ; Fay and Popper
2012 ). Their hypothesis of the ear evolving in response to “auditory scene analysis,” while largely untested, was a central reason for us to test the acoustic soundscape of the cave and surface environments in our work and formed the
underpinnings of much of what we were trying to assess. In addition, their longstanding interest in the evolution of fi sh hearing greatly infl uenced all three of us
to use the cave- and surface-dwelling species as a natural experiment to test
hypotheses fi rst laid out in the seminal papers of these two senior bioacousticians
(Fay and Popper 2012 ). Both have also served a personal mentoring role for two of
the authors of this current work, as they have done for the vast majority of researchers in this fi eld.
D. Soares et al.