168
was determined to have performed an AEBR. AEBRs served as proxies for the ASR
when using a non-high-speed camera to record the responses because the ASR
occurs on the timescale of ~5–10 ms and standard (30 frames per second) cameras
have a temporal resolution of ~33 ms. The authors were able to use this technique
to show group-level absolute thresholds for larval zebrafi sh in early development
(from 5 to 26 days dpf).
We have used the ASR to determine how auditory thresholds differ during early
development in two distantly related species of fi sh. Zebrafi sh ( D. rerio , order
Cypriniformes) have specialized accessory structures for hearing, whereas the
three-spined sticklebacks ( Gasterosteus aculeatus , order Gasterosteiformes) are
non-specialists that lack specialized accessory hearing structures. Fishes with hearing specializations generally have greater auditory sensitivity and frequency bandwidth detection than fi sh species that do not (Popper and Fay 2011 ). However,
whether these differences are present before the development of hearing specializations is not known. The ASR is a useful method to probe an animal’s auditory system in terms of auditory sensitivity and frequency detection capability at hearing
onset because it is rapid and can be retested over time.
Using the apparatus described by Bhandiwad et al. ( 2013 ), we presented pure
tone stimuli to larval three-spined sticklebacks and zebrafi sh. We fi rst used the kinematics of the startle response to determine whether startle responses of larval sticklebacks were similar to those found in larval zebrafi sh (Fig. 6 ). Sticklebacks that
were tested consisted of Japan Pacifi c, Paxton Lake Limnetic, and Paxton Lake
Benthic species and were chosen due to their morphological differences in lateral
line and therefore represented the diversity of stickleback species (Wark and Peichel
2010 ). We show that the kinematics of the startle response in both zebrafi sh and
sticklebacks are essentially the same, although the maximal bend angle is much
smaller in sticklebacks (Fig. 7 ). Because both species’ startle responses are on the
same timescale, we posited that they are both mediated by the M-cell pathway.
Next, we tested groups of larval stickleback fi sh daily from the day they became
free swimming until they exhibited the ASR. In zebrafi sh, the onset of the ASR to
pure tones is 5 dpf (Zeddies and Fay 2005 ; Bhandiwad et al. 2013 ), but ASRs can
be evoked earlier by an acoustic broadband stimulus at 4 dpf (Fig. 8 ). In contrast,
sticklebacks begin to exhibit ASRs to broadband acoustic stimuli at 9 days post
hatch (dph) and showed frequency-specifi c differences in ASR onset. Post-hatch
days were more accurate measures of development in sticklebacks due to the long
duration and variability of the embryonic period; in comparison, all zebrafi sh larvae
hatched at 3 dpf. Low frequency stimuli (e.g., 45 Hz) evoked ASRs in sticklebacks
at 12 ± 2 dph (mean ± SD), but higher frequency stimuli (e.g., 90 Hz) did not evoke
ASRs until 15 ± 1 dph. These data suggest that there may be an ontogenetic change
in frequency sensitivity of larval sticklebacks during early development from 9 to
16 dph. ASRs evoked by either pure tones or broadband stimuli were all-or-none
response in both zebrafi sh and sticklebacks.
Auditory thresholds on the day of hearing onset also differed between larval
zebrafi sh and sticklebacks. Because there were frequency-dependent differences in
ASR onset, sticklebacks were tested between 24 and 31 dph. No signifi cant differA.A. Bhandiwad and J.A. Sisneros
was determined to have performed an AEBR. AEBRs served as proxies for the ASR
when using a non-high-speed camera to record the responses because the ASR
occurs on the timescale of ~5–10 ms and standard (30 frames per second) cameras
have a temporal resolution of ~33 ms. The authors were able to use this technique
to show group-level absolute thresholds for larval zebrafi sh in early development
(from 5 to 26 days dpf).
We have used the ASR to determine how auditory thresholds differ during early
development in two distantly related species of fi sh. Zebrafi sh ( D. rerio , order
Cypriniformes) have specialized accessory structures for hearing, whereas the
three-spined sticklebacks ( Gasterosteus aculeatus , order Gasterosteiformes) are
non-specialists that lack specialized accessory hearing structures. Fishes with hearing specializations generally have greater auditory sensitivity and frequency bandwidth detection than fi sh species that do not (Popper and Fay 2011 ). However,
whether these differences are present before the development of hearing specializations is not known. The ASR is a useful method to probe an animal’s auditory system in terms of auditory sensitivity and frequency detection capability at hearing
onset because it is rapid and can be retested over time.
Using the apparatus described by Bhandiwad et al. ( 2013 ), we presented pure
tone stimuli to larval three-spined sticklebacks and zebrafi sh. We fi rst used the kinematics of the startle response to determine whether startle responses of larval sticklebacks were similar to those found in larval zebrafi sh (Fig. 6 ). Sticklebacks that
were tested consisted of Japan Pacifi c, Paxton Lake Limnetic, and Paxton Lake
Benthic species and were chosen due to their morphological differences in lateral
line and therefore represented the diversity of stickleback species (Wark and Peichel
2010 ). We show that the kinematics of the startle response in both zebrafi sh and
sticklebacks are essentially the same, although the maximal bend angle is much
smaller in sticklebacks (Fig. 7 ). Because both species’ startle responses are on the
same timescale, we posited that they are both mediated by the M-cell pathway.
Next, we tested groups of larval stickleback fi sh daily from the day they became
free swimming until they exhibited the ASR. In zebrafi sh, the onset of the ASR to
pure tones is 5 dpf (Zeddies and Fay 2005 ; Bhandiwad et al. 2013 ), but ASRs can
be evoked earlier by an acoustic broadband stimulus at 4 dpf (Fig. 8 ). In contrast,
sticklebacks begin to exhibit ASRs to broadband acoustic stimuli at 9 days post
hatch (dph) and showed frequency-specifi c differences in ASR onset. Post-hatch
days were more accurate measures of development in sticklebacks due to the long
duration and variability of the embryonic period; in comparison, all zebrafi sh larvae
hatched at 3 dpf. Low frequency stimuli (e.g., 45 Hz) evoked ASRs in sticklebacks
at 12 ± 2 dph (mean ± SD), but higher frequency stimuli (e.g., 90 Hz) did not evoke
ASRs until 15 ± 1 dph. These data suggest that there may be an ontogenetic change
in frequency sensitivity of larval sticklebacks during early development from 9 to
16 dph. ASRs evoked by either pure tones or broadband stimuli were all-or-none
response in both zebrafi sh and sticklebacks.
Auditory thresholds on the day of hearing onset also differed between larval
zebrafi sh and sticklebacks. Because there were frequency-dependent differences in
ASR onset, sticklebacks were tested between 24 and 31 dph. No signifi cant differA.A. Bhandiwad and J.A. Sisneros