Geographical variation in sound production in the anemonefish Amphiprion akallopisos

Sounding the Call for a Global Library of Underwater Biological Sounds

Aquatic environments encompass the world’s most extensive habitats, rich with sounds produced by a diversity of animals. Passive acoustic monitoring (PAM) is an increasingly accessible remote sensing technology that uses hydrophones to listen to the underwater world and represents an unprecedented, non-invasive method to monitor underwater environments. This information can assist in the delineation of biologically important areas via detection of sound-producing species or characterization of ecosystem type and condition, inferred from the acoustic properties of the local soundscape. At a time when worldwide biodiversity is in significant decline and underwater soundscapes are being altered as a result of anthropogenic impacts, there is a need to document, quantify, and understand biotic sound sources–potentially before they disappear. A significant step toward these goals is the development of a web-based, open-access platform that provides: (1) a reference library of known and unknown biological sound sources (by integrating and expanding existing libraries around the world); (2) a data repository portal for annotated and unannotated audio recordings of single sources and of soundscapes; (3) a training platform for artificial intelligence algorithms for signal detection and classification; and (4) a citizen science-based application for public users. Although individually, these resources are often met on regional and taxa-specific scales, many are not sustained and, collectively, an enduring global database with an integrated platform has not been realized. We discuss the benefits such a program can provide, previous calls for global data-sharing and reference libraries, and the challenges that need to be overcome to bring together bio- and ecoacousticians, bioinformaticians, propagation experts, web engineers, and signal processing specialists (e.g., artificial intelligence) with the necessary support and funding to build a sustainable and scalable platform that could address the needs of all contributors and stakeholders into the future.

Characterization of the acoustic community of vocal fishes in the Azores

Sounds produced by teleost fishes are an important component of marine soundscapes, making passive acoustic monitoring (PAM) an effective way to map the presence of vocal fishes with a minimal impact on ecosystems. Based on a literature review, we list the known soniferous fish species occurring in Azorean waters and compile their sounds. We also describe new fish sounds recorded in Azores seamounts. From the literature, we identified 20 vocal fish species present in Azores. We analysed long-term acoustic recordings carried out since 2008 in Condor and Princesa Alice seamounts and describe 20 new putative fish sound sequences. Although we propose candidates as the source of some vocalizations, this study puts into evidence the myriad of fish sounds lacking species identification. In addition to identifying new sound sequences, we provide the first marine fish sound library for Azores. Our acoustic library will allow to monitor soniferous fish species for conservation and management purposes.

Causes and Consequences of Sensory Hair Cell Damage and Recovery in Fishes

Sensory hair cells are the mechanotransductive receptors that detect gravity, sound, and vibration in all vertebrates. Damage to these sensitive receptors often results in deficits in vestibular function and hearing. There are currently two main reasons for studying the process of hair cell loss in fishes. First, fishes, like other non-mammalian vertebrates, have the ability to regenerate hair cells that have been damaged or lost via exposure to ototoxic chemicals or acoustic overstimulation. Thus, they are used as a biomedical model to understand the process of hair cell death and regeneration and find therapeutics that treat or prevent human hearing loss. Secondly, scientists and governmental natural resource managers are concerned about the potential effects of intense anthropogenic sounds on aquatic organisms, including fishes. Dr. Arthur N. Popper and his students, postdocs and research associates have performed pioneering experiments in both of these lines of fish hearing research. This review will discuss the current knowledge regarding the causes and consequences of both lateral line and inner ear hair cell damage in teleost fishes.

Sound production mechanism in Gobius paganellus (Gobiidae)

Gobiidae, the largest fish family (>1500 species), has species from at least 10 genera that produce sounds for communication. Studies focused on goby sound production mechanisms have suggested that sounds are produced by the forcible ejection of water through small apertures in the opercles (hydrodynamic mechanism). The present study was a multidisciplinary investigation (morphology, muscle histology, high-speed video, sound analysis and electromyography) of the sound emission mechanism in Gobius paganellus, which produces both pulsed and tonal calls. Two populations were used, from Brittany and Venice. In the French population, sounds were accompanied by a suite of coordinated movements of the buccal, branchial and opercular regions. This was not the case in the Venetian population, and thus the direct role of head movements in sound production was rejected. The hydrodynamic mechanism hypothesis was also rejected in G. paganellus on the basis of sound oscillogram shape and because sounds are still produced after the opercles and hyohyoid muscles are cut. The use of both electromyography and electron microscopy showed that the levator pectoralis muscle, which originates on the skull and inserts on the dorsal tip of the cleithrum, is involved in sound production. We propose that the contraction of this muscle and associated vibration of the large radials is used to make sounds. In addition, we propose that different sound types (pulsed sounds and tonal calls) could occur because of differences in fish size.

Behaviours associated with acoustic communication in Nile tilapia (Oreochromis niloticus)

Background

Sound production is widespread among fishes and accompanies many social interactions. The literature reports twenty-nine cichlid species known to produce sounds during aggressive and courtship displays, but the precise range in behavioural contexts is unclear. This study aims to describe the various Oreochromis niloticus behaviours that are associated with sound production in order to delimit the role of sound during different activities, including agonistic behaviours, pit activities, and reproduction and parental care by males and females of the species.

Methodology/Principal Findings

Sounds mostly occur during the day. The sounds recorded during this study accompany previously known behaviours, and no particular behaviour is systematically associated with sound production. Males and females make sounds during territorial defence but not during courtship and mating. Sounds support visual behaviours but are not used alone. During agonistic interactions, a calling Oreochromis niloticus does not bite after producing sounds, and more sounds are produced in defence of territory than for dominating individuals. Females produce sounds to defend eggs but not larvae.

Conclusion/Significance

Sounds are produced to reinforce visual behaviours. Moreover, comparisons with O. mossambicus indicate two sister species can differ in their use of sound, their acoustic characteristics, and the function of sound production. These findings support the role of sounds in differentiating species and promoting speciation. They also make clear that the association of sounds with specific life-cycle roles cannot be generalized to the entire taxa.

Overview on the diversity of sounds produced by clownfishes (Pomacentridae): importance of acoustic signals in their peculiar way of life

Background

Clownfishes (Pomacentridae) are brightly colored coral reef fishes well known for their mutualistic symbiosis with tropical sea anemones. These fishes live in social groups in which there is a size-based dominance hierarchy. In this structure where sex is socially controlled, agonistic interactions are numerous and serve to maintain size differences between individuals adjacent in rank. Clownfishes are also prolific callers whose sounds seem to play an important role in the social hierarchy. Here, we aim to review and to synthesize the diversity of sounds produced by clownfishes in order to emphasize the importance of acoustic signals in their way of life.

Methodology/Principal Findings

Recording the different acoustic behaviors indicated that sounds are divided into two main categories: aggressive sounds produced in conjunction with threat postures (charge and chase), and submissive sounds always emitted when fish exhibited head shaking movements (i.e. a submissive posture). Both types of sounds showed size-related intraspecific variation in dominant frequency and pulse duration: smaller individuals produce higher frequency and shorter duration pulses than larger ones, and inversely. Consequently, these sonic features might be useful cues for individual recognition within the group. This observation is of significant importance due to the size-based hierarchy in clownfish group. On the other hand, no acoustic signal was associated with the different reproductive activities.

Conclusions/Significance

Unlike other pomacentrids, sounds are not produced for mate attraction in clownfishes but to reach and to defend the competition for breeding status, which explains why constraints are not important enough for promoting call diversification in this group.

Mutualism with sea anemones triggered the adaptive radiation of clownfishes

Background

Adaptive radiation is the process by which a single ancestral species diversifies into many descendants adapted to exploit a wide range of habitats. The appearance of ecological opportunities, or the colonisation or adaptation to novel ecological resources, has been documented to promote adaptive radiation in many classic examples. Mutualistic interactions allow species to access resources untapped by competitors, but evidence shows that the effect of mutualism on species diversification can greatly vary among mutualistic systems. Here, we test whether the development of obligate mutualism with sea anemones allowed the clownfishes to radiate adaptively across the Indian and western Pacific oceans reef habitats.

Results

We show that clownfishes morphological characters are linked with ecological niches associated with the sea anemones. This pattern is consistent with the ecological speciation hypothesis. Furthermore, the clownfishes show an increase in the rate of species diversification as well as rate of morphological evolution compared to their closest relatives without anemone mutualistic associations.

Conclusions

The effect of mutualism on species diversification has only been studied in a limited number of groups. We present a case of adaptive radiation where mutualistic interaction is the likely key innovation, providing new insights into the mechanisms involved in the buildup of biodiversity. Due to a lack of barriers to dispersal, ecological speciation is rare in marine environments. Particular life-history characteristics of clownfishes likely reinforced reproductive isolation between populations, allowing rapid species diversification.

Interspecific variation of calls in clownfishes: degree of similarity in closely related species

BACKGROUND

Clownfishes are colorful coral reef fishes living in groups in association with sea anemones throughout the Indo-Pacific Ocean. Within their small societies, size hierarchy determines which fish have access to reproduction. These fishes are also prolific callers whose aggressive sounds seem to play an important role in the social hierarchy. Agonistic interactions being involved in daily behaviour suggest how acoustic communication might play an important role in clownfish group. Sounds were recorded and compared in fourteen clownfish species (some of which have never been recorded before) to evaluate the potential role of acoustic communication as an evolutionary driving force.

RESULTS

Surprisingly, the relationship between fish size and both dominant frequency and pulse duration is not only species-specific; all the specimens of the 14 species are situated on exactly the same slope, which means the size of any Amphiprion can be predicted by both acoustic features. The number of pulses broadly overlaps among species, whereas the pulse period displays the most variation even if it shows overlap among sympatric species. Sound comparisons between three species (A. akallopisos, A. ocellaris and A. frenatus) having different types of teeth and body shape do not show differences neither in the acoustic waveform nor in the power spectrum.

CONCLUSION

Significant overlap in acoustic features demonstrates that the sound-producing mechanism is highly conservative among species. Differences in the calls of some species are due to size dimorphism and the sound variation might be in this case a by-product. This morphological constraint does not permit a consideration of acoustic communication as the main driving force in the diversification of clownfishes. Moreover, calls are not produced to find mate and consequently are less subject to variations due to partner preference, which restricts the constraints of diversification. Calls are produced to reach and defend the competition to mate access. However, differences in the pulse period between cohabiting species show that, in some case, sounds can help to differentiate the species, to prevent competition between cohabiting species and to promote the diversification of taxa.

Comparative study on sound production in different Holocentridae species

BACKGROUND

Holocentrids (squirrelfish and soldierfish) are vocal reef fishes whose calls and sound-producing mechanisms have been studied in some species only. The present study aims to compare sound-producing mechanisms in different Holocentridae genera (Holocentrus, Myripristis, Neoniphon, Sargocentron) from separate regions and, in some cases, at different developmental stages. An accurate comparison was made by recording six species while being hand-held, by observing TEM) the sonic muscles and by dissections of the sound-producing mechanism.

RESULTS

In all these species, calls presented harmonics, their dominant frequency was between 80 and 130 Hz and they were composed of trains of 4 to 11 pulses with gradual increasing periods towards the end of the call. In each case, the calls did not provide reliable information on fish size. The sounds were produced by homologous fast-contracting sonic muscles that insert on articulated ribs whose proximal heads are integrated into the swimbladder: each pulse is the result of the back and forth movements of the ribs. Small differences in the shape of the oscillograms of the different species could be related to the number of ribs that are involved in the sound-producing mechanism. These fish species are able to make sounds as soon as they settle on the reef, when they are 40 days old. Comparison between Neoniphon from Madagascar and from Rangiroa in French Polynesia showed a new, unexpected kind of dialect involving differences at the level of pulse distribution. Neoniphon calls were characterised by a single pulse that was isolated at the beginning of the remaining train in Madagascar whereas they did not show any isolated single pulses at the beginning of the call in Rangiroa.

CONCLUSION

This family cannot use the acoustic fundamental frequencies (or pulse periods) of grunts to infer the size of partners. Pulse duration and number of pulses are statistically related to fish size. However, these characteristics are poorly informative because the correlation slope values are weak. It remains other features (sound amplitude, resistance to muscle fatigue, calling frequency) could be used to assess the body size. Characteristics of the sound producing mechanisms are conservative. All species possess fast-contracting muscles and have the same kind of sound producing mechanism. They do show some change between clades but these differences are not important enough to deeply modify the waveforms of the calls. In this case, our description of the grunt could be considered as the signature for the holocentrid family and can be used in passive acoustic monitoring.

Calls of the black drum (Pogonias cromis: Sciaenidae): geographical differences in sound production between northern and southern hemisphere populations

Because of apparent reproductive isolation between Northern and Southern hemisphere populations of the black drum Pogonius cromis, we tested the hypothesis that advertisement calls from a southern population would differ from known calls of North American populations. Additionally, we quantified disturbance and advertisement calls, their changes with fish size and sex, not previously examined in this species. Unlike most sciaenids, both sexes of P. cromis possess robust sonic muscles, and both produce disturbance calls when handled. However, only males produce an advertisement call used in courtship. The disturbance call consists of a variable train of short-duration pulses (average 23 ms). The duration, interpulse interval, and dominant frequency of pulses are similar in males and females and change developmentally: pulse duration and interpulse interval increase and dominant frequency decreases with fish size. Advertisement calls, recorded in the field and in captivity, are long-duration (average 184 ms) and tonal. Based on variation in fundamental frequency, which decreases with fish size, field choruses are composed of different-sized individuals. The duration of advertisement calls, about a third of those from Florida populations, suggests genetic differentiation between northern and southern populations.

A noisy spring: the impact of globally rising underwater sound levels on fish

The underwater environment is filled with biotic and abiotic sounds, many of which can be important for the survival and reproduction of fish. Over the last century, human activities in and near the water have increasingly added artificial sounds to this environment. Very loud sounds of relatively short exposure, such as those produced during pile driving, can harm nearby fish. However, more moderate underwater noises of longer duration, such as those produced by vessels, could potentially impact much larger areas, and involve much larger numbers of fish. Here we call attention to the urgent need to study the role of sound in the lives of fish and to develop a better understanding of the ecological impact of anthropogenic noise.

Agonistic sounds in the skunk clownfish Amphiprion akallopisos: size-related variation in acoustic features

Fourteen individuals of the skunk clownfish Amphiprion akallopisos of different sizes and of different sexual status (non-breeder, male or female) were analysed for four acoustic features. Dominant frequency and pulse duration were highly correlated with standard length (r = 0.97), and were not related to sex. Both the dominant frequency and pulse duration were signals conveying information related to the size of the emitter, which implies that these sound characteristics could be useful in assessing size of conspecifics.

Novel vocal repertoire and paired swimbladders of the three-spined toadfish, Batrachomoeus trispinosus: insights into the diversity of the Batrachoididae

Toadfishes (Teleostei: Batrachoididae) are one of the best-studied groups for understanding vocal communication in fishes. However, sounds have only been recorded from a low proportion of taxa within the family. Here, we used quantitative bioacoustic, morphological and phylogenetic methods to characterize vocal behavior and mechanisms in the three-spined toadfish, Batrachomoeus trispinosus. B. trispinosus produced two types of sound: long-duration 'hoots' and short-duration 'grunts' that were multiharmonic, amplitude and frequency modulated, with a dominant frequency below 1 kHz. Grunts and hoots formed four major classes of calls. Hoots were typically produced in succession as trains, while grunts occurred either singly or as grunt trains. Aside from hoot trains, grunts and grunt trains, a fourth class of calls consisted of single grunts with acoustic beats, apparently not previously reported for individuals from any teleost taxon. Beats typically had a predominant frequency around 2 kHz with a beat frequency around 300 Hz. Vocalizations also exhibited diel and lunar periodicities. Spectrographic cross-correlation and principal coordinates analysis of hoots from five other toadfish species revealed that B. trispinosus hoots were distinct. Unlike any other reported fish, B. trispinosus had a bilaterally divided swimbladder, forming two separate swimbladders. Phylogenetic analysis suggested B. trispinosus was a relatively basal batrachoidid, and the swimbladder and acoustic beats were independently derived. The swimbladder in B. trispinosus demonstrates that toadfishes have undergone a diversification of peripheral sonic mechanisms, which may be responsible for the concomitant innovations in vocal communication, namely the individual production of acoustic beats as reported in some tetrapods.

Sound production and spectral hearing sensitivity in the Hawaiian sergeant damselfish, Abudefduf abdominalis

Sounds provide important signals for inter- and intraspecific communication in fishes, but few studies examine fish acoustic behavior in the context of coevolution of sound production and hearing ability within a species. This study characterizes the acoustic behavior in a reproductive population of the Hawaiian sergeant fish, Abudefduf abdominalis, and compares acoustic features to hearing ability, measured by the auditory evoked potential (AEP)technique. Sergeant fish produce sounds at close distances to the intended receiver (⩽1–2 body lengths), with different pulse characteristics that are associated primarily with aggression, nest preparation and courtship–female-visit behaviors. Energy peaks of all sounds were between 90 and 380 Hz, whereas courtship–visit sounds had a pulse repetition rate of 125 Hz with harmonic intervals up to 1 kHz. AEP threshold,which is probably higher than the behavioral threshold, indicates best sensitivity at low frequencies (95–240 Hz), with the lowest threshold at 125 Hz (123–127 dBrms re: 1 μPa). Thus, sound production and hearing in A. abdominalis are closely matched in the frequency domain and are useful for courtship and mating at close distances. Measured hearing thresholds did not differ among males and females during spawning or non-spawning periods, which indicates a lack of sex differences and seasonal variation in hearing capabilities. These data provide the first evidence that Abudefduf uses true acoustic communication on a level similar to that of both more derived (e.g. Dascyllus, Chromis) and more basal (e.g. Stegastes) soniferous pomacentrids. This correlation between sound production and hearing ability is consistent with the sensory drive model of signal evolution in which the sender and receiver systems coevolve within the constraints of the environment to maximize information transfer of acoustic signals.