Characterization of the primary sonic muscles in Carapus acus (Carapidae): a multidisciplinary approach

Sound production and mechanism in the cryptic cusk-eel Parophidion vassali

This study investigates the sounds and the anatomy of the sound-producing organ in the male and female sand-dwelling cusk-eel Parophidion vassali. Although both sexes have similar external phenotype, they can be distinguished by their sonic apparatus and sounds. As in many Ophioidei, Parophidion vassali presents a panel of highly derived characters. Fish possess three pairs of sonic muscles, and males have mineralized swimbladder caps on which inserts the ventral sonic muscle, a neural arch that pivots, a stretchable swimbladder fenestra, an osseous swimbladder plate and a rounded pressure-release membrane in the caudal swimbladder. Females, however, do not possess anterior swimbladder caps, a swimbladder fenestra and the caudal rounded membrane. Males possess the unusual ability to produce sounds starting with a set of low amplitude pulses followed by a second set with higher amplitudes clearly dividing each sound unit into two parts. Females do not vary their sound amplitude in this way: they produce shorter sounds and pulse periods but with a higher peak frequency. Morphology and sound features support the sound-producing mechanism is based on a rebound system (i.e. quick backward snap of the anterior swimbladder). Based on features of the sounds from tank recordings, we have putatively identified the sound of male Parophidion vassali at sea. As these species are ecologically cryptic, we hope this work will allow assessment and clarify the distribution of their populations.

Functional Adaptation of Vocalization Revealed by Morphological and Histochemical Characteristics of Sonic Muscles in Blackmouth Croaker (Atrobucca nibe)

Simple Summary

Sound production is common in numerous fish species. Some species can emit calls through the contraction of specialized muscles called sonic or drumming muscles. The sonic muscles of fish are among the fastest muscles in vertebrates. Although numerous studies have investigated the mechanism underlying sound production in fish, only the distinct features of the sonic muscles of a few species have been investigated. We demonstrated that the sonic muscles have functionally adapted for fast twitching and fatigue resistance, which support vocalization in the blackmouth croaker (Atrobucca nibe).

Abstract

Sound production in the blackmouth croaker (Atrobucca nibe) was characterized using acoustic, morphological, and histochemical methods. Their calls consisted of a train of two to seven pulses; the frequency ranged from 180 to 3000 Hz, with a dominant frequency of 326 ± 40 Hz. The duration of each call ranged from 80 to 360 ms. Male A. nibe possess a pair of bilaterally symmetric sonic muscles attached to the body wall adjacent to the swim bladder. The average diameter of the sonic muscle fibers was significantly shorter than that of the abdominal muscle fibers. Semithin sections of the sonic muscle fibers revealed a core-like structure (central core) and the radial arrangement of the sarcoplasmic reticulum and myofibrils. Numerous mitochondria were distributed within the central core and around the periphery of the fibers. Most of the fibers were identified as Type IIa on the basis of their myosin adenosine triphosphatase activities, but a few were identified as Type IIc fibers. All sonic muscle fibers exhibited strong oxidative enzyme activity and oxidative and anaerobic capabilities. The features suggest that the sonic muscles of A. nibe are morphologically and physiologically adapted for fast twitching and fatigue resistance, which support fish vocalization.

Global knowledge on the commercial sea cucumber Holothuria scabra

Holothuria scabra is one of the most intensively studied holothuroids, or sea cucumbers (Echinodermata: Holothuroidea), having been discussed in the literature since the early 19th century. The species is important for several reasons: (1) it is widely distributed and historically abundant in several shallow soft-bottom habitats throughout the Indo-Pacific, (2) it has a high commercial value on the Asian markets, where it is mainly sold as a dried product (beche-de-mer) and (3) it is the only tropical holothuroid species that can currently be mass-produced in hatcheries. Over 20 years have elapsed since the last comprehensive review on H. scabra published in 2001. Research on H. scabra has continued to accumulate, fuelled by intense commercial exploitation, and further declines in wild stocks over the entire distribution range. This review compiles data from over 950 publications pertaining to the biology, ecology, physiology, biochemical composition, aquaculture, fishery, processing and trade of H. scabra, presenting the most complete synthesis to date, including scientific papers and material published by local institutions and/or in foreign languages. The main goal of this project was to summarize and critically discuss the abundant literature on this species, making it more readily accessible to all stakeholders aiming to conduct fundamental and applied research on H. scabra, or wishing to develop aquaculture, stock enhancement and management programs across its geographic range.

Modifications in call characteristics and sonic apparatus morphology during puberty in Ophidion rochei (Actinopterygii: Ophidiidae)

Juveniles, females, and males of Ophidion rochei share similar external morphology, probably because they are mainly active in the dark, which reduces the role of visual cues. Their internal sonic apparatuses, however, are complex: three pairs of sonic muscles, and highly modified vertebrae and ribs are involved in sound production. The sonic apparatus of males differs from juveniles and females in having larger swimbladder plates (modified ribs associate with the swimbladder wall) and sonic muscles, a modified swimbladder shape and a mineralized structure called the "rocker bone" in front of the swimbladder. All of these male traits appear at the onset of sexual maturation. This article investigates the relationship between morphology and sounds in male O. rochei of different sizes. Despite their small size range total length (133-170 mm TL), the five specimens showed pronounced differences in sound-production apparatus morphology, especially in terms of swimbladder shape and rocker bone development. This observation was reinforced by the positive allometry measured for the rocker bone and the internal tube of the swimbladder. The differences in morphology were related to marked differences in sound characteristics (especially frequency and pulse duration). These results suggest that male calls carry information about the degree of maturity. Deprived of most visual cues, ophidiids probably have invested in other mechanisms to recognize and distinguish among individual conspecifics and between ophidiid species. As a result, their phenotypes are externally similar but internally very different. In these taxa, the great variability of the sound production apparatus means this complex system is a main target of environmental constraints.

Hearing capacities and otolith size in two ophidiiform species (Ophidion rochei and Carapus acus)

Numerous studies have highlighted the diversity of fish inner ear morphology. However, the function of shape, size, and orientation of the different structures remains poorly understood. The saccule (otolithic endorgan) is considered as the principal hearing organ in fishes and it has been hypothesized that sagitta (saccular otolith) shape and size affect hearing capacities: large sagittae are thought to increase sensitivity. The sagittae of many ophidiids and carapids occupy a large volume inside the neurocranium. Hence they are of great interest to test the size hypothesis. The main aim of this study was to investigate hearing capacities and inner ear morphology in two ophidiiform species: Ophidion rochei and Carapus acus. We used a multidisciplinary approach that combines dissections, μCT-scan examinations, and auditory evoked potential technique. Carapus acus and O. rochei sagittae have similar maximal diameter, both species have larger otoliths than many non-ophidiiform species especially compared to the intra-neurocranium (INC) volume. Both species are sensitive to sounds up to 2100 Hz. Relative to the skull, O. rochei had smaller sagittae than the carapid but better hearing capacities from 300 to 900 Hz and similar sensitivities at 150 Hz and from 1200 to 2100 Hz. Results show that hearing capacities of a fish species cannot be predicted only based on sagitta size. Larger otoliths (in size relative to the skull) may have evolved mainly for performing vestibular functions in fishes, especially those ones that need to execute precise and complex movements.

A superfast muscle in the complex sonic apparatus of Ophidion rochei (Ophidiiformes): histological and physiological approaches

In teleosts, superfast muscles are generally associated with the swimbladder wall whose vibrations result in sound production. In Ophidion rochei, three pairs of muscles were named 'sonic' because their contractions affect swimbladder position: the dorsal sonic muscle (DSM), the intermediate sonic muscle (ISM), and the ventral sonic muscle (VSM). These muscles were investigated thanks to electron microscopy and electromyography in order to determine their function in sound production. Fibers of the VSM and DSM were much thinner than the fibers of the ISM and epaxial musculature. However, only VSM fibers had the typical ultrastructure of superfast muscles: low proportion of myofibrils, and high proportions of sarcoplasmic reticulum and mitochondria. In females, each sound onset was preceded by the onset of electrical activity in the VSM and the DSM (ISM was not tested). The electromyograms of the VSM were very similar to the waveforms of the sounds: means for the pulse period were 3.6±0.5 ms and 3.6±0.7 ms, respectively. This shows that the fast VSM (ca. 280 Hz) is responsible for the pulse period and fundamental frequency of female sounds. DSM electromyograms were generally characterized by one or two main peaks followed by periods of lower electrical activity which suggests a sustained contraction over the course of the sound. The fiber morphology of the ISM and its antagonistic position relative to the DSM are not indicative of a muscle capable of superfast contractions. Overall, this study experimentally shows the complexity of the sound production mechanism in the nocturnal fish O. rochei.

Parvalbumin characteristics in the sonic muscle of a freshwater ornamental grunting toadfish (Allenbatrachus grunniens)

The grunting toadfish, Allenbatrachus grunniens, is an ornamental fish in freshwater aquariums, and it has the ability to produce sounds. The sonic muscle of the toadfish is the fastest vertebrate muscle ever measured, and the rates of Ca(2+) transport and cross-bridge dissociation are also the fastest. Parvalbumins (PAs) are Ca(2+)-binding proteins that help in muscle relaxation in vertebrates. Several PA isoforms have been identified in variable ratios in different muscle types. Both male and female grunting toadfish have intrinsic sonic muscles attached to their swim bladders, but no significant difference in morphology between male and female sonic muscles has been observed. In this study, we used SDS-PAGE and western blotting to characterize the total PA expression and to identify the PAs from the sonic muscle and the white body muscle of A. grunniens. Although the total PA concentrations were similar in sonic and white muscles, there were differences in the isoform percentages. Two and four PA isoforms were identified from sonic muscle and white muscle, respectively. The estimated sizes of PA1, PA2, and PA3 in the sonic muscle of the grunting toadfish were 10, 10.5, and 10.5 kDa, respectively, and the isoelectric points of PA1, PA2, and PA3 in the grunting toadfish were 4.77, 4.58, and 4.42, respectively. In the sonic muscle, the primary PA isoform was PA1, which comprised more than 94 % of total PA, whereas PA2 comprised only 5 % of the total PA content. In contrast, in white muscle, the primary isoform was PA2, which comprised 58 % of the total PA. Both PA1 (with PA1a) and PA3 represented approximately 20 % of the total PA in white muscle. These results indicate that there is no positive correlation between a high PA content and the speed of muscle relaxation; however, PA1 might have the greatest effect on the relaxation of the grunting toadfish's sonic muscle.

Seasonal changes in atrophy-associated proteins of the sonic muscle in the big-snout croaker, Johnius macrorhynus (Pisces, Sciaenidae), identified by using a proteomic approach

In most sciaenids, males possess sonic muscles and produce sound through the contraction of these muscles and amplification of the swim bladder. The sonic muscles in some fishes exhibit seasonal changes in size. For example, they are hypertrophic in the spawning season, and atrophic in the non-spawning months. The protein profiles of the sonic muscle, red muscle, and white muscle in the Johnius macrorhynus were shown by two-dimensional electrophoresis (2-DE) and were compared to reveal differential protein expressions. About 80 up-regulated protein spots in the sonic muscle, and 30 spots related to six contractile proteins (fast muscle myosin heavy chain, skeletal alpha actin, alpha actin cardiac, tropomyosin, myosin light chain 2, and myosin light chain 3), four energy metabolic enzymes (enolase, acyl-CoA synthetase, creatine kinase, and cytochrome P450 monooxygenase), and two miscellaneous proteins (DEAD box protein and cyclin H) were identified. Seasonal hypertrophy and atrophy of the sonic muscles related to the reproductive cycle were verified in male big-snout croaker. The contents of some proteins were significantly different in the muscles under these conditions. The levels of cytochrome P450 monooxygenase, fast muscle myosin heavy chain, DEAD box proteins, isocitrate dehydrogenase, and creatine kinase were up-regulated in the hypertrophic muscle, but the levels of alpha actin cardiac, myosin light 2, and myosin light 3 were lower than in the atrophic muscle. Potential reasons for these differences in protein expression related to physiological adaptation are discussed.

Sound production and mechanism in Heniochus chrysostomus (Chaetodontidae)

The diversity in calls and sonic mechanisms appears to be important in Chaetodontidae. Calls in Chaetodon multicinctus seem to include tail slap, jump, pelvic fin flick and dorsal–anal fin erection behaviors. Pulsatile sounds are associated with dorsal elevation of the head, anterior extension of the ventral pectoral girdle and dorsal elevation of the caudal skeleton in Forcipiger flavissiumus. In Hemitaurichthys polylepis, extrinsic swimbladder muscles could be involved in sounds originating from the swimbladder and correspond to the inward buckling of tissues situated dorsally in front of the swimbladder. These examples suggest that this mode of communication could be present in other members of the family. Sounds made by the pennant bannerfish (Heniochus chrysostomus) were recorded for the first time on coral reefs and when fish were hand held. In hand-held fishes, three types of calls were recorded: isolated pulses (51%), trains of four to 11 pulses (19%) and trains preceded by an isolated pulse (29%). Call frequencies were harmonic and had a fundamental frequency between 130 and 180 Hz. The fundamental frequency, sound amplitude and sound duration were not related to fish size. Data from morphology, sound analysis and electromyography recordings highlight that the calls are made by extrinsic sonic drumming muscles in association with the articulated bones of the ribcage. The pennant bannerfish system differs from other Chaetodontidae in terms of sound characteristics, associated body movements and, consequently, mechanism.

Is high concentration of parvalbumin a requirement for superfast relaxation?

It is generally thought that the rapid relaxation of fast muscles is facilitated by the Ca(2+) binding protein parvalbumin (Parv). Indeed superfast swimbladder (SWB) muscle of toadfish contains the largest concentration of this protein ever observed (up to 1.5 mM). At 15 degrees C toadfish perform a 100 Hz call, 400 ms in duration, followed by a long (5-15 s) intercall interval. It has been proposed that Parv helps sequester the Ca(2+) during the call, and then Ca(2+) unbinds and is pumped back into the sarcoplasmic reticulum during the long intercall interval. Midshipman (Porichthys notatus) is another fish which calls at a high frequency; 80-100 Hz at a temperature of 12-15 degrees C. However, unlike toadfish, midshipman call with a 100% duty cycle. Without an intercall interval, Parv would seem of little use as it would become saturated early in calling. Here we show that the midshipman SWB has only about 1/8th of the Parv in toadfish. Moreover, total Parv content in calling male midshipman SWB was not different from that in the non-calling female and the much slower locomotory muscles. These data suggest that Parv does not play a large role in the calling of midshipman, which is accomplished without a high concentration of this protein. Native gel-electrophoresis also revealed presence of three major (PA-I, PA-II and PA-III) and two minor (PA-Ia and PA-IIIa, <5% of total content) Parv isoforms in adult toadfish SWB. Midshipman SWB contained about equal amounts of PA-I and PA-II and also a small (approximately 10%) amount of PA-III. By amino acid composition, toadfish PA-Ia and PA-I isoforms were different from PA-II and PA-III isoforms (by 24 and 14 residues, respectively).

Superfast vocal muscles control song production in songbirds

Birdsong is a widely used model for vocal learning and human speech, which exhibits high temporal and acoustic diversity. Rapid acoustic modulations are thought to arise from the vocal organ, the syrinx, by passive interactions between the two independent sound generators or intrinsic nonlinear dynamics of sound generating structures. Additionally, direct neuromuscular control could produce such rapid and precisely timed acoustic features if syringeal muscles exhibit rare superfast muscle contractile kinetics. However, no direct evidence exists that avian vocal muscles can produce modulations at such high rates. Here, we show that 1) syringeal muscles are active in phase with sound modulations during song over 200 Hz, 2) direct stimulation of the muscles in situ produces sound modulations at the frequency observed during singing, and that 3) syringeal muscles produce mechanical work at the required frequencies and up to 250 Hz in vitro. The twitch kinematics of these so-called superfast muscles are the fastest measured in any vertebrate muscle. Superfast vocal muscles enable birds to directly control the generation of many observed rapid acoustic changes and to actuate the millisecond precision of neural activity into precise temporal vocal control. Furthermore, birds now join the list of vertebrate classes in which superfast muscle kinetics evolved independently for acoustic communication.

Parvalbumin correlates with relaxation rate in the swimming muscle of sheepshead and kingfish

Parvalbumin is a muscle protein that aids in relaxation from contraction. Parvalbumin binds myoplasmic Ca(2+) during contractions, reducing calcium concentration and enhancing relaxation. Different isoforms of parvalbumin have varying affinities for calcium, and relaxation rates in skeletal muscle may be affected by variations in the isoforms of parvalbumin expressed. This study examines the effect of expression levels of parvalbumin isoforms on relaxation rate in the sheepshead, Archosargus probatocephalus (Pisces, F. Sparidae). We measured relaxation rate of each of the three fiber types, white (fast-twitch), red (slow-twitch) and pink (intermediate), from three longitudinal body positions. Sheepshead show a significant longitudinal shift in relaxation rate in red muscle, with anterior muscle displaying faster rates of relaxation than posterior, but this pattern was not significant in the pink and white muscle. We hypothesized that patterns of parvalbumin expression determine relaxation rate along the length of the fish. The prediction is that total parvalbumin content and the relative expression of parvalbumin isoforms will differ between the anterior and posterior red muscle, but little longitudinal variation will be observed in parvalbumin expression in white and pink muscle. We successfully employed protein electrophoresis (SDS-PAGE) with western blots to identify two parvalbumin isoforms in each muscle fiber type. SDS-PAGE and densitometry were used to determine the relative expression levels of the two parvalbumin isoforms and total parvalbumin expression. Red muscle displays a significant shift, from anterior to posterior, in the relative expression of the two isoforms, both in their relative contribution and in total parvalbumin content, but white and pink muscle did not. The red muscle of southern kingfish, Menticirrhus americanus (Pisces, F. Scianidae) showed a pattern similar to the red muscle of sheepshead.

Sound production mechanism in carapid fish: first example with a slow sonic muscle

Fish sonic swimbladder muscles are the fastest muscles in vertebrates and have fibers with numerous biochemical and structural adaptations for speed. Carapid fishes produce sounds with a complex swimbladder mechanism, including skeletal components and extrinsic sonic muscle fibers with an exceptional helical myofibrillar structure. To study this system we stimulated the sonic muscles, described their insertion and action and generated sounds by slowly pulling the sonic muscles. We find the sonic muscles contract slowly, pulling the anterior bladder and thereby stretching a thin fenestra. Sound is generated when the tension trips a release system that causes the fenestra to snap back to its resting position. The sound frequency does not correspond to the calculated resonant frequency of the bladder, and we hypothesize that it is determined by the snapping fenestra interacting with an overlying bony swimbladder plate. To our knowledge this tension release mechanism is unique in animal sound generation.

Syringeal muscles fit the trill in ring doves (Streptopelia risoriaL.)

In contrast to human phonation, the virtuoso vocalizations of most birds are modulated at the level of the sound generator, the syrinx. We address the hypothesis that syringeal muscles are physiologically capable of controlling the sound-generating syringeal membranes in the ring dove (Streptopelia risoria) syrinx. We establish the role of the tracheolateralis muscle and propose a new function for the sternotrachealis muscle. The tracheolateralis and sternotrachealis muscles have an antagonistic mechanical effect on the syringeal aperture. Here, we show that both syringeal muscles can dynamically control the full syringeal aperture. The tracheolateralis muscle is thought to directly alter position and tension of the vibrating syringeal membranes that determine the gating and the frequency of sound elements. Our measurements of the muscle's contractile properties, combined with existing electromyographic and endoscopic evidence, establish its modulating role during the dove's trill. The muscle delivers the highest power output at cycle frequencies that closely match the repetition rates of the fastest sound elements in the coo. We show that the two syringeal muscles share nearly identical contraction characteristics, and that sternotrachealis activity does not clearly modulate during the rapid trill. We propose that the sternotrachealis muscle acts as a damper that stabilizes longitudinal movements of the sound-generating system induced by tracheolateralis muscle contraction. The extreme performance of both syringeal muscles implies that they play an important role in fine-tuning membrane position and tension, which determines the quality of the sound for a conspecific mate.

Functional morphology of the sonic apparatus inOphidion barbatum (Teleostei, Ophidiidae)

Most soniferous fishes producing sounds with their swimbladder utilize relatively simple mechanisms: contraction and relaxation of a unique pair of sonic muscles cause rapid movements of the swimbladder resulting in sound production. Here we describe the sonic mechanism for Ophidion barbatum, which includes three pairs of sonic muscles, highly transformed vertebral centra and ribs, a neural arch that pivots and a swimbladder whose anterior end is modified into a bony structure, the rocker bone. The ventral and intermediate muscles cause the rocker bone to swivel inward, compressing the swimbladder, and this action is antagonized by the dorsal muscle. Unlike other sonic systems in which the muscle contraction rate determines sound fundamental frequency, we hypothesize that slow contraction of these antagonistic muscles produces a series of cycles of swimbladder vibration.

Aspects of sound communication in the pearlfishCarapus boraborensis andCarapus homei (Carapidae)

Several species of Carapidae are known to have symbiotic relationships with marine invertebrates. The two most common species in Moorea (French Polynesia), Carapus boraborensis and Carapus homei, undergo conspecific and heterospecific encounters in the same holothurian host during which they produce sounds. Another characteristic of these fish lies in their abilities to produce sounds. The objective of this study was dual: (1) to seek if there was a sexual difference in the sounds produced by C. boraborensis; (2) to seek if there was a difference in the sound emissions between heterospecific and conspecific encounters. In each trial, sounds were only recorded when one individual entered the sea cucumber that was already occupied. In encounters, sounds were structured in regular pulse emissions whose pulse lengths and periods allowed to significantly distinguish each species, as well as both sexes in C. boraborensis. In the latter species, results show for the first time that temporal features of the emitted sounds can have a functional importance in sex identification. In heterospecific encounters, sounds were reduced 68% of the time to a single pulse emission and there was a modification in the pulse length of each species: it shortens in C. homei and it lengthens in C. boraborensis. It highlights that both carapids are able to adapt their sounds to the facing species. Because a modification of the sound appears to be done at the first emission, it is supposed that recognition precedes the sound emission.