Acoustical properties of the swimbladder in the oyster toadfish Opsanus tau

Functional plasticity of the swim bladder as an acoustic organ for communication in a vocal fish

Teleost fishes have evolved a number of sound-producing mechanisms, including vibrations of the swim bladder. In addition to sound production, the swim bladder also aids in sound reception. While the production and reception of sound by the swim bladder has been described separately in fishes, the extent to which it operates for both in a single species is unknown. Here, using morphological, electrophysiological and modelling approaches, we show that the swim bladder of male plainfin midshipman fish (Porichthys notatus) exhibits reproductive state-dependent changes in morphology and function for sound production and reception. Non-reproductive males possess rostral 'horn-like' swim bladder extensions that enhance low-frequency (less than 800 Hz) sound pressure sensitivity by decreasing the distance between the swim bladder and inner ear, thus enabling pressure-induced swim bladder vibrations to be transduced to the inner ear. By contrast, reproductive males display enlarged swim bladder sonic muscles that enable the production of advertisement calls but also alter swim bladder morphology and increase the swim bladder to inner ear distance, effectively reducing sound pressure sensitivity. Taken together, we show that the swim bladder exhibits a seasonal functional plasticity that allows it to effectively mediate both the production and reception of sound in a vocal teleost fish.

An investigation of bubble resonance and its implications for sound production by deep-water fishes

Although the continental slope and abyss comprise the largest habitat on earth, the absence of documented fish sounds from deep waters is striking. Fishes with sexually dimorphic muscles attached to their swim bladders suggests that sounds are likely used in male courtship on the upper, mid and lower continental slope. To investigate the effects of environmental extremes on fish sound production, the acoustic behavior of a driven bubble is examined. This study is also relevant to target strength of sonar returns from fish and hearing in auditory specialist fishes. A bubble is a classic, if imperfect, model for swim bladder behavior since the swim-bladder wall is an anisotropic viscoelastic structure responsible for rapid damping. Acoustic properties of bubbles–including far-field resonant frequency, damping factor, and quality factor–are calculated in warm and cold surface conditions and in cold deep-water (depths 1000 m, 2000 m, and 3500 m) conditions using parameters for oxygen and nitrogen, the dominant gases in swim bladders. The far-field resonant frequency and damping factor of a bubble increase with depth, and the scattering cross-section and quality factor decrease with depth. These acoustic properties scale with undamped oscillation frequency of the bubble and do not vary significantly due to gas type or temperature. Bubbles in the deep-water environments are much less efficient radiators of sound than bubbles near the surface because the far-field radiated power for the same excitation decreases with depth. A bubble at depth 3500 m has a 25 dB loss in radiated sound power compared to the same-radius bubble at the surface. This reduction of radiation efficiency in deep water likely contributes to the absence of fish sound recordings in those environments.

Evolutionary and Biomechanical Basis of Drumming Behavior in Woodpeckers

Understanding how and why behavioral traits diversify during the course of evolution is a longstanding goal of organismal biologists. Historically, this topic is examined from an ecological perspective, where behavioral evolution is thought to occur in response to selection pressures that arise through different social and environmental factors. Yet organismal physiology and biomechanics also play a role in this process by defining the types of behavioral traits that are more or less likely to arise. Our paper explores the interplay between ecological, physiological, and mechanical factors that shape the evolution of an elaborate display in woodpeckers called the drum. Individuals produce this behavior by rapidly hammering their bill on trees in their habitat, and it serves as an aggressive signal during territorial encounters. We describe how different components of the display—namely, speed (bill strikes/beats sec–1), length (total number of beats), and rhythm—differentially evolve likely in response to sexual selection by male-male competition, whereas other components of the display appear more evolutionarily static, possibly due to morphological or physiological constraints. We synthesize research related to principles of avian muscle physiology and ecology to guide inferences about the biomechanical basis of woodpecker drumming. Our aim is to introduce the woodpecker as an ideal study system to study the physiological basis of behavioral evolution and how it relates to selection born through different ecological factors.

Simultaneous production of two kinds of sounds in relation with sonic mechanism in the boxfish Ostracion meleagris and O. cubicus

In fishes, sonic abilities for communication purpose usually involve a single mechanism. We describe here the sonic mechanism and sounds in two species of boxfish, the spotted trunkfish Ostracion meleagris and the yellow boxfish Ostracion cubicus. The sonic mechanism utilizes a T-shaped swimbladder with a swimbladder fenestra and two separate sonic muscle pairs. Extrinsic vertical muscles attach to the vertebral column and the swimbladder. Perpendicularly and below these muscles, longitudinal intrinsic muscles cover the swimbladder fenestra. Sounds are exceptional since they are made of two distinct types produced in a sequence. In both species, humming sounds consist of long series (up to 45 s) of hundreds of regular low-amplitude pulses. Hums are often interspersed with irregular click sounds with an amplitude that is ten times greater in O. meleagris and forty times greater in O. cubicus. There is no relationship between fish size and many acoustic characteristics because muscle contraction rate dictates the fundamental frequency. We suggest that hums and clicks are produced by either separate muscles or by a combination of the two. The mechanism complexity supports an investment of boxfish in this communication channel and underline sounds as having important functions in their way of life.

Wall structure and material properties cause viscous damping of swimbladder sounds in the oyster toadfish Opsanus tau

Despite rapid damping, fish swimbladders have been modelled as underwater resonant bubbles. Recent data suggest that swimbladders of sound-producing fishes use a forced rather than a resonant response to produce sound. The reason for this discrepancy has not been formally addressed, and we demonstrate, for the first time, that the structure of the swimbladder wall will affect vibratory behaviour. Using the oyster toadfish Opsanus tau, we find regional differences in bladder thickness, directionality of collagen layers (anisotropic bladder wall structure), material properties that differ between circular and longitudinal directions (stress, strain and Young's modulus), high water content (80%) of the bladder wall and a 300-fold increase in the modulus of dried tissue. Therefore, the swimbladder wall is a viscoelastic structure that serves to damp vibrations and impart directionality, preventing the expression of resonance.

Unusual sound production mechanism in the triggerfish Rhinecanthus aculeatus (Balistidae)

The ability to produce sounds has been known for decades in Balistidae. Sounds of many species have been recorded and a variety of sound producing mechanisms have been proposed including teeth stridulation, collision of buccal teeth, and movements of the fins. The best supported hypothesis involves movements of the pectoral fins against the lateral parts of the swimbladder called a drumming membrane. In this study, we describe for the first time the sounds made by the Blackbar triggerfish Rhinecanthus aculeatus that sound like short drum rolls with an average duration of 85 ms, 193 Hz dominant frequency and 136 dB SPL level at 3 cm distance. Sounds are a series of pulses that result from alternate sweeping movements of the right and left pectoral fins, which push a system of three scutes that are forced against the swimbladder wall. Pulses from each fin occur in consecutive pairs. High-speed videos indicate that each pulse consists in two cycles. The first part of each cycle corresponds to the inward buckling of the scutes whereas the second part of the cycle corresponds to an apparent passive recoil of the scutes and swimbladder wall. This novel sound production mechanism is likely found in many members of Balistidae because these peculiar scutes are found in other species in the family. Comparison of sound characteristics from fishes of different sizes shows that dominant frequency decreases with size in juveniles but not in adults.

Vocalisations of the bigeye Pempheris adspersa: characteristics, source level and active space

Fish sounds are an important biological component of the underwater soundscape. Understanding species-specific sounds and their associated behaviour is critical for determining how animals use the biological component of the soundscape. Using both field and laboratory experiments, we describe the sound production of a nocturnal planktivore, Pempheris adspersa (New Zealand bigeye), and provide calculations for the potential effective distance of the sound for intraspecific communication. Bigeye vocalisations recorded in the field were confirmed as such by tank recordings. They can be described as popping sounds, with individual pops of short duration (7.9±0.3 ms) and a peak frequency of 405±12 Hz. Sound production varied during a 24 h period, with peak vocalisation activity occurring during the night, when the fish are most active. The source level of the bigeye vocalisation was 115.8±0.2 dB re. 1 µPa at 1 m, which is relatively quiet compared with other soniferous fish. Effective calling range, or active space, depended on both season and lunar phase, with a maximum calling distance of 31.6 m and a minimum of 0.6 m. The bigeyes' nocturnal behaviour, characteristics of their vocalisation, source level and the spatial scale of its active space reported in the current study demonstrate the potential for fish vocalisations to function effectively as contact calls for maintaining school cohesion in darkness.

Variation in swim bladder drumming sounds from three doradid catfish species with similar sonic morphologies

A variety of teleost fishes produce sounds for communication by vibrating the swim bladder with fast contracting muscles. Doradid catfishes have an elastic spring apparatus (ESA) for sound production. Contractions of the ESA protractor muscle pull the anterior transverse process of the 4th vertebra or Müllerian ramus (MR) to expand the swim bladder and elasticity of the MR returns the swim bladder to the resting state. In this study, we examined the sound characteristics and associated fine structure of the protractor drumming muscles of three doradid species: Acanthodoras cataphractus, Platydoras hancockii, and Agamyxis pectinifrons. Despite important variations in sizes, sounds from all three species had similar mean dominant rates ranging from 91-131 Hz and showed frequencies related to muscle contraction speed rather than fish size. Sounds differed among species in terms of waveform shape and their rate of amplitude modulation. In addition, multiple distinguishable sound types were observed from each species: three sound types from A. cataphractus and P. hancockii, and two sound types from A. pectinifrons. Though sounds differed among species, no differences in muscle fiber fine structure were observed at the species level. Drumming muscles from each species bear features associated with fast contractions, including sarcoplasmic cores, thin radial myofibrils, abundant mitochondria, and an elaborated sarcoplasmic reticulum. These results indicate that sound differences between doradids are not due to swimbladder size, muscle anatomy, muscle length, or Müllerian ramus shape, but instead result from differences in neural activation of sonic muscles.

Diversity and evolution of sound production in the social behavior of Chaetodon butterflyfishes

Fish produce context-specific sounds during social communication but it is not known how acoustic behaviors have evolved in relation to specializations of the auditory system. Butterflyfishes (family Chaetodontidae) have a well-defined phylogeny and produce pulsed communication sounds during social interactions on coral reefs. Recent work indicates two sound production mechanisms exist in the bannerfish clade and others for one species in the Chaetodon clade which is distinguished by an auditory specialization, the laterophysic connection (LC). We determine the kinematic action patterns associated with sound production during social interactions in four Chaetodon subgenera and the non-laterophysic Forcipiger. Some Chaetodon species share the head bob acoustic behavior with Forcipiger which along with other sounds in the 100-1000 Hz spectrum are likely adequate to stimulate the ear, swim bladder or LC of a receiver fish. In contrast, only Chaetodon produced the tail slap sound which involves a 1-30 Hz hydrodynamic pulse that likely stimulates the receiver's ear and lateral line at close distances, but neither the swim bladder nor LC. Reconstructions of ancestral character states appear equivocal for the head bob and divergent for the tail slap acoustic behaviors. Independent contrast analysis shows a correlation between sound duration and stimulus intensity characters. The intensity of the tail slap and body pulse sound in Chaeotodon is correlated with body size and can provide honest communication signals. Future studies on fish acoustic communication should investigate low frequency and infrasound acoustic fields to understand the integrated function of the ear and lateral line, and their evolutionary patterns.

Vocal production complexity correlates with neural instructions in the oyster toadfish (Opsanus tau)

Sound communication is fundamental to many social interactions and essential to courtship and agonistic behaviours in many vertebrates. The swimbladder and associated muscles in batrachoidid fishes (midshipman and toadfish) is a unique vertebrate sound production system, wherein fundamental frequencies are determined directly by the firing rate of a vocal-acoustic neural network that drives the contraction frequency of superfast swimbladder muscles. The oyster toadfish boatwhistle call starts with an irregular sound waveform that could be an emergent property of the peripheral nonlinear sound-producing system or reflect complex encoding in the central nervous system. Here, we demonstrate that the start of the boatwhistle is indicative of a chaotic strange attractor, and tested whether its origin lies in the peripheral sound-producing system or in the vocal motor network. We recorded sound and swimbladder muscle activity in awake, freely behaving toadfish during motor nerve stimulation, and recorded sound, motor nerve and muscle activity during spontaneous grunts. The results show that rhythmic motor volleys do not cause complex sound signals. However, arrhythmic recruitment of swimbladder muscle during spontaneous grunts correlates with complex sounds. This supports the hypothesis that the irregular start of the boatwhistle is encoded in the vocal pre-motor neural network, and not caused by peripheral interactions with the sound-producing system. We suggest that sound production system demands across vocal tetrapods have selected for muscles and motorneurons adapted for speed, which can execute complex neural instructions into equivalently complex vocalisations.

Development of the ultrastructure of sonic muscles: a kind of neoteny?

Background

Drumming muscles of some sound-producing fish are ‘champions’ of contraction speed, their rate setting the fundamental frequency. In the piranha, contraction of these muscles at 150 Hz drives a sound at the same frequency. Drumming muscles of different not closely related species show evolutionary convergences. Interestingly, some characters of sonic muscles can also be found in the trunk muscles of newly hatched larvae that are able to maintain tail beat frequencies up to 100 Hz. The aim of this work was to study the development of sound production and sonic and epaxial muscles simultaneously in the red bellied piranhas (Pygocentrus nattereri) to seek for possible common characteristics.

Results

Call, pulse and period durations increased significantly with the fish size, but the call dominant frequencies decreased, and the number of pulses and the call amplitude formed a bell curve. In epaxial muscles, the fibre diameters of younger fish are first positioned in the graphical slope corresponding to sonic muscles, before diverging. The fibre diameter of older fish trunk muscles was bigger, and the area of the myofibrils was larger than in sonic muscles. Moreover, in two of the biggest fish, the sonic muscles were invaded by fat cells and the sonic muscle ultrastructure was similar to the epaxial one. These two fish were also unable to produce any sound, meaning they lost their ability to contract quickly.

Conclusions

The volume occupied by myofibrils determines the force of contraction, the volume of sarcoplasmic reticulum sets the contraction frequency, and the volume of mitochondria sets the level of sustained performance. The functional outcomes in muscles are all attributable to shifts in the proportions of those structures. A single delay in the development restricts the quantity of myofibrils, maintains a high proportion of space in the sarcoplasm and develops sarcoplasmic reticulum. High-speed sonic muscles could thus be skeletal muscles with delayed development. This hypothesis has the advantage that it could easily explain why high-speed sonic muscles have evolved so many times in different lineages.

Vocal corollary discharge communicates call duration to vertebrate auditory system

Corollary discharge is essential to an animal's ability to filter self-generated from external stimuli. This includes acoustic communication, although direct demonstration of a corollary discharge that both conveys a vocal motor signal and informs the auditory system about the physical attributes of a self-generated vocalization has remained elusive for vertebrates. Here, we show the underlying synaptic activity of a neuronal vocal corollary discharge pathway in the hindbrain of a highly vocal species of fish. Neurons carrying the vocal corollary discharge are specifically adapted for the transmission of duration information, a predominant acoustic cue. The results reveal that vertebrates, like some insects, have a robust corollary discharge conveying call duration. Along with evidence for the influence of vocal duration on auditory encoding in mammals, these new findings suggest that linking vocal motor and corollary discharge pathways with pattern generating, call duration neurons is a shared network character across the animal kingdom.

Novel underwater soundscape: acoustic repertoire of plainfin midshipman fish

Toadfishes are among the best-known groups of sound producing (vocal) fishes and include species commonly known as toadfish and midshipman. Although midshipman have been the subject of extensive investigation of the neural mechanisms of vocalization, this is the first comprehensive, quantitative analysis of the spectro-temporal characters of their acoustic signals and one of the few for fishes in general. Field recordings of territorial, nest-guarding male midshipman during the breeding season identified a diverse vocal repertoire comprised of three basic sound types that varied widely in duration, harmonic structure, and degree of amplitude modulation (AM) - "hum", "grunt", and "growl". Hum duration varied nearly 1000 fold, lasting for minutes at a time, with stable harmonic stacks and little envelope modulation throughout the sound. By contrast, grunts were brief, ~30-140 ms, broadband signals produced both in isolation and repetitively as a train of up to 200 at intervals of ~0.5-1.0 s. Growls were also produced alone or repetitively, but at variable intervals on the order of seconds with durations between that of grunts and hums, ranging 60 fold from ~200 ms - 12 s. Growls exhibited prominent harmonics with sudden shifts in pulse repetition rate and highly variable AM patterns, unlike the nearly constant AM of grunt trains and flat envelope of hums. Behavioral and neurophysiological studies support the hypothesis that each sound type's unique acoustic signature contributes to signal recognition mechanisms. Nocturnal production of these sounds against a background chorus dominated constantly for hours by a single sound type, the multi-harmonic hum, reveals a novel underwater soundscape for fish.

Further insight into the sound-producing mechanism of clownfishes: what structure is involved in sound radiation?

It was recently demonstrated that clownfishes produce aggressive sounds by snapping their jaw teeth. To date, only the onset of the sound has been studied, which raises the question, what structure is involved in sound radiation? Here, a combination of different approaches has been used to determine the anatomical structure(s) responsible for the size-related variations observed in sound duration and frequency. Filling the swimbladder with physiological liquid specifically modified size-related acoustic features by inducing a significant decrease in pulse duration of approximately 3 ms and a significant increase in dominant frequency of approximately 105 Hz. However, testing the acoustics of the swimbladder by striking it with a piezoelectric impact hammer showed that this structure is a highly damped sound source prevented from prolonged vibrations. In contrast, the resonant properties of the rib cage seems to account for the size-related variations observed in acoustic features. For an equivalent strike on the rib cage, the duration and dominant frequency of induced sounds changed with fish size: sound duration and dominant frequency were positively and negatively correlated with fish size, respectively. Such relationships between sonic features and fish size are consistent with those observed in natural sounds emitted by fish. Therefore, the swimbladder itself does not act as a resonator; its wall just seems to be driven by the oscillations of the rib cage. This set of observations suggests the need for reassessment of the acoustic role of swimbladders in various fish species.

An Intermediate in the evolution of superfast sonic muscles

BACKGROUND

Intermediate forms in the evolution of new adaptations such as transitions from water to land and the evolution of flight are often poorly understood. Similarly, the evolution of superfast sonic muscles in fishes, often considered the fastest muscles in vertebrates, has been a mystery because slow bladder movement does not generate sound. Slow muscles that stretch the swimbladder and then produce sound during recoil have recently been discovered in ophidiiform fishes. Here we describe the disturbance call (produced when fish are held) and sonic mechanism in an unrelated perciform pearl perch (Glaucosomatidae) that represents an intermediate condition in the evolution of super-fast sonic muscles.

RESULTS

The pearl perch disturbance call is a two-part sound produced by a fast sonic muscle that rapidly stretches the bladder and an antagonistic tendon-smooth muscle combination (part 1) causing the tendon and bladder to snap back (part 2) generating a higher-frequency and greater-amplitude pulse. The smooth muscle is confirmed by electron microscopy and protein analysis. To our knowledge smooth muscle attachment to a tendon is unknown in animals.

CONCLUSION

The pearl perch, an advanced perciform teleost unrelated to ophidiiform fishes, uses a slow type mechanism to produce the major portion of the sound pulse during recoil, but the swimbladder is stretched by a fast muscle. Similarities between the two unrelated lineages, suggest independent and convergent evolution of sonic muscles and indicate intermediate forms in the evolution of superfast muscles.

Sound production in red-bellied piranhas (Pygocentrus nattereri, Kner): an acoustical, behavioural and morphofunctional study

Piranhas are known to be sound-producing animals. Nevertheless, the biological significance of piranha calls remains unclear because sounds have been recorded only when specimens were held by hand or trapped in a gill net. These sounds are generated by rapid contractions of sonic muscles that insert on a broad tendon surrounding ventrally the cranial sac of the swimbladder. The piranha swimbladder is thought to play an important role in sound production as an impedance-matching device and as a resonator. However, the vibratory capacities of the cranial and caudal sacs and the exact role of both sacs in sound production remain poorly understood. In this study, three sounds were each associated to a specific behaviour. The first sound (type 1) was produced during frontal display; it had numerous pulses and lasted 140!±17 ms, with a fundamental frequency of 120±4 Hz. It corresponded to the sound made by hand-held fishes. The second sound (type 2) was produced during circling and fighting behaviour; it was a single pulse lasting 36±8 ms, with a fundamental frequency of 43±10 Hz. The third sound (type 3) corresponded to chasing behaviour and comprised three to four pulses, each lasting 3±1 ms, with a fundamental frequency of 1739±18 Hz. Using a laser vibrometer to study the swimbladder displacement when stimulated at different frequencies, it was demonstrated that the first two sounds corresponded to the swimbladder mechanism. By contrast, the third sound was associated with the jaw mechanism. The vibrometer indicated that the swimbladder is a highly damping structure, simply copying the sonic muscle contraction rate. This study provides two interesting insights. First, it shows the relationships between three kinds of piranha sound and three specific behaviours. Second, using muscle stimulation at different rates, it shows which simultaneous conditions are required for production of sound in this species. Swimbladder calls were produced by a muscle contraction rate of approximately 100 Hz because this periodicity allowed the swimbladder to vibrate. At this frequency range, the contraction–relaxation cycles of the swimbladder muscles engendered wall displacements that had short amplitudes and with only a small variability between them.

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.