Larval settlement in flocculated particulates

Author Posting. © The Authors, 2008. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 66 (2008): 275-297, doi:10.1357/002224008785837167.Planktonic larval settlement can be a major determinant of population and community dynamics. Settlement templates of benthic invertebrates have been attributed to biological, chemical, and hydrodynamic mechanisms. Completely unexplored, however, is the role of patchy, but widespread, flocculated particulates (“floc”) that intermittently rest on substrate surfaces. Motivated by observations of very high (of order 106 m-3) larval/postlarval densities in floc from a coastal embayment, this study experimentally identified physical and behavioral mechanisms responsible for these associations. In annular-flume studies, sediment cores were mounted flush with the channel bottom, serving as the floc source. Larval (Capitella sp. I, a polychaete worm) distributions in the flume were consistent with predictions for transported particulates. Floc and larvae accumulated at the channel inner corner in high flows (shear velocities, u*, of 0.8 and 1.6 cm s-1), but not in low flows (u* of 0, 0.2 and 0.4 cm s-1). Inner-corner concentrations of larvae/floc resulted from a predictable, cross-channel, bottom flow in that direction. In still-water behavioral assays, there were no significant differences in percent metamorphosis among flocs fabricated from particulate-laden seawater, conspecific fecal pellets (compact floc) and organic-rich sediment. Surficial aggregates clearly were acceptable settlement substratum. This study is the first to show that settling larvae associate with surficial aggregates via both physical and behavioral mechanisms. Floc may be a transient larval venue facilitating habitat search, providing nutrition, or offering protection from predators. Alternatively, it could confer high mortality, reducing larval flux to the bed. Associations between larvae and floc do not supersede established mechanisms of habitat selection. They just thicken the plot.This study was supported by the National Science Foundation (OCE 97-29972 and OCE 02-42321), NOAA California Sea Grant College Program (R/F-197) and the UCLA Council on Research

Ultrasound-evoked immediate early gene expression in the brainstem of the Chinese torrent frog, Odorrana tormota

The concave-eared torrent frog, Odorrana tormota, has evolved the extraordinary ability to communicate ultrasonically (i.e., using frequencies>20kHz), and electrophysiological experiments have demonstrated that neurons in the frog’s midbrain (torus semicircularis) respond to frequencies up to 34kHz. However, at this time, it is unclear which region(s) of the torus and what other brainstem nuclei are involved in the detection of ultrasound. To gain insight into the anatomical substrate of ultrasound detection, we mapped expression of the activity-dependent gene, egr-1, in the brain in response to a full-spectrum mating call, a filtered, ultrasound-only call, and no sound. We found that the ultrasound-only call elicited egr-1 expression in the superior olivary and principal nucleus of the torus semicircularis. In sampled areas of the principal nucleus, the ultrasound-only call tended to evoke higher egr-1 expression than the full-spectrum call and, in the center of the nucleus, induced significantly higher egr-1 levels than the no-sound control. In the superior olivary nucleus, the full-spectrum and ultrasound-only calls evoked similar levels of expression that were significantly greater than the control, and egr-1 induction in the laminar nucleus showed no evidence of acoustic modulation. These data suggest that the sampled areas of the principal nucleus are among the regions sensitive to ultrasound in this species

Ultrasound-evoked immediate early gene expression in the brainstem of the Chinese torrent frog, Odorrana tormota

The concave-eared torrent frog, Odorrana tormota, has evolved the extraordinary ability to communicate ultrasonically (i.e., using frequencies > 20 kHz), and electrophysiological experiments have demonstrated that neurons in the frog’s midbrain (torus semicircularis) respond to frequencies up to 34 kHz. However, at this time, it is unclear which region(s) of the torus and what other brainstem nuclei are involved in the detection of ultrasound. To gain insight into the anatomical substrate of ultrasound detection, we mapped expression of the activity-dependent gene, egr-1, in the brain in response to a full-spectrum mating call, a filtered, ultrasound-only call, and no sound. We found that the ultrasound-only call elicited egr-1 expression in the superior olivary and principal nucleus of the torus semicircularis. In sampled areas of the principal nucleus, the ultrasound-only call tended to evoke higher egr-1 expression than the full-spectrum call and, in the center of the nucleus, induced significantly higher egr-1 levels than the no-sound control. In the superior olivary nucleus, the full-spectrum and ultrasound-only calls evoked similar levels of expression that were significantly greater than the control, and egr-1 induction in the laminar nucleus showed no evidence of acoustic modulation. These data suggest that the sampled areas of the principal nucleus are among the regions sensitive to ultrasound in this species

Pure ultrasonic communication in an endemic Bornean frog.

Huia cavitympanum, an endemic Bornean frog, is the first amphibian species known to emit exclusively ultrasonic (i.e., >20 kHz) vocal signals. To test the hypothesis that these frogs use purely ultrasonic vocalizations for intraspecific communication, we performed playback experiments with male frogs in their natural calling sites. We found that the frogs respond with increased calling to broadcasts of conspecific calls containing only ultrasound. The field study was complemented by electrophysiological recordings from the auditory midbrain and by laser Doppler vibrometer measurements of the tympanic membrane's response to acoustic stimulation. These measurements revealed that the frog's auditory system is broadly tuned over high frequencies, with peak sensitivity occurring within the ultrasonic frequency range. Our results demonstrate that H. cavitympanum is the first non-mammalian vertebrate described to communicate with purely ultrasonic acoustic signals. These data suggest that further examination of the similarities and differences in the high-frequency/ultrasonic communication systems of H. cavitympanum and Odorrana tormota, an unrelated frog species that produces and detects ultrasound but does not emit exclusively ultrasonic calls, will afford new insights into the mechanisms underlying vertebrate high-frequency communication

Ultrasonic signalling by a Bornean frog

Among anuran amphibians, only two species, Odorrana tormota and Huia cavitympanum, are known to possess recessed tympanic membranes. Odorrana tormota is the first non-mammalian vertebrate demonstrated to communicate with ultrasonic frequencies (above 20 kHz), and the frogs' sunken tympana are hypothesized to play a key role in their high-frequency hearing sensitivity. Here we present the first data on the vocalizations of H. cavitympanum. We found that this species emits extraordinarily high-frequency calls, a portion of which are comprised entirely of ultrasound. This represents the first documentation of an anuran species producing purely ultrasonic signals. In addition, the vocal repertoire of H. cavitympanum is highly variable in frequency modulation pattern and spectral composition. The frogs' use of vocal signals with a wide range of dominant frequencies may be a strategy to maximize acoustic energy transmission to both nearby and distant receivers. The convergence of these species' call characteristics should stimulate additional, phylogenetically based studies of other lower vertebrates to provide new insight into the mechanistic and evolutionary foundations of high-frequency hearing in all vertebrate forms

Number of calls emitted and calling rate during playback trials.

<p>Trials are organized by stimulus presentation order and playback rate. Blocks (3 min each) are identified as No Stimulus (NS), Ultrasonic (US), Background noise (negative) control (BKG), and Audible (AUD). Italicized values are the number of calls emitted by the focal male during each block. Numbers in bold are calling rates (calls/min) during US stimulus presentation. For the first five frogs in the table, the US and BKG stimuli were presented once per 10 s.</p>*<p>Calling rate during the first minute of the US block when the stimulus was presented once per second, and during the second 2 min when the stimulus was presented once per 10 s.</p>**<p>Calling rate for the US stimulus presented once per 5 s.</p

Number of calls emitted in playback categories included in the statistical analysis.

<p>PreUS-NS and PreBKG-NS are the No Stimulus blocks preceding the Ultrasonic and Background noise blocks, respectively. Bold values are the number of calls emitted during NS periods following US or AUD blocks; this calling activity may result from the post-stimulus excitatory state of the frog. The difference in the average number of calls produced during the blocks is statistically significant (P = .008), and the number of calls emitted during the US stimulus periods is significantly higher than the average number produced during the PreBKG-NS blocks (Wilcoxon Signed Ranks, P = .043).</p