Mismatch between shape changes and ecological shifts during the post-settlement growth of the surgeonfish, <i>Acanthurus triostegus</i>

Background: Many coral reef fishes undergo habitat and diet shifts during ontogeny. However, studies focusing on the physiological and morphological adaptations that may prepare them for these transitions are relatively scarce. Here, we explored the body shape variation related to ontogenetic shifts in the ecology of the surgeonfish Acanthurus triostegus (Acanthuridae) from new settler to adult stages at Moorea Island (French Polynesia). Specifically, we tested the relationship between diet and habitat shifts and changes in overall body shape during the ontogeny of A. triostegus using a combination of geometric morphometric methods, stomach contents and stable isotope analysis.Results: After reef settlement, stable isotope composition of carbon and nitrogen revealed a change from a zooplanktivorous to a benthic algae diet. The large amount of algae (> 75% of stomach contents) found in the digestive tract of small juveniles (25–30 mm SL) suggested the diet shift is rapid. The post-settlement growth of A. triostegus is highly allometric. The allometric shape changes mainly concern cephalic and pectoral regions. The head becomes shorter and more ventrally oriented during growth. Morphological changes are directly related to the diet shift given that a small mouth ventrally oriented is particularly suited for grazing activities at the adult stage. The pectoral fin is more anteriorely and vertically positioned and its basis is larger in adults than in juveniles. This shape variation had implications for swimming performance, manoeuvrability, turning ability and is related to habitat shift. Acanthurus triostegus achieves its main transformation of body shape to an adult-like form at size of 35–40 mm SL. Conclusion: Most of the shape changes occurred after the reef colonization but before the transition between juvenile habitat (fringing reef) and adult habitat (barrier reef). A large amount of allometric variation was observed after diet shift from zooplankton to benthic algae. Diet shift could act as an environmental factor favouring or inducing morphological changes. On the other hand, the main shape changes have to be achieved before the recruitment to adult populations and start negotiating the biophysical challenges of locomotion and feeding in wave- and current-swept outer reef habitat

Histological study of the sex-change in the skunk clownfish <i>Amphiprion akallopisos</i>

Sex change in the protandrous fish Amphiprion akallopisos Bleeker, 1853 (F.Pomacentridae) has been analysed. Experiments consisted of placing males together after being separated from their mates, and observe changes in gonad histology at different periods, in order to identify signs of the sex change process. The presence of a first invagination on the male gonad wall, and the observation of the first cortical alveoli oocytes as an indication of the beginning of the vitellogenesis process, was the first symptom of the sex change, which has been detected after 18 days in one of the males. Period needed for the sex changing process was size independent. The process by which wall invagination is converted into ovarian lumen in the future mature ovary is also described

Histological study of the sex-change in the skunk clownfish Amphiprion akallopisos

peer reviewedSex change in the protandrous fish Amphiprion akallopisos Bleeker, 1853 (F.Pomacentridae) has been analysed. Experiments consisted of placing males together after being separated from their mates, and observe changes in gonad histology at different periods, in order to identify signs of the sex change process. The presence of a first invagination on the male gonad wall, and the observation of the first cortical alveoli oocytes as an indication of the beginning of the vitellogenesis process, was the first symptom of the sex change, which has been detected after 18 days in one of the males. Period needed for the sex changing process was size independent. The process by which wall invagination is converted into ovarian lumen in the future mature ovary is also described

Auditory evoked potential audiograms in post-settlement stage individuals of coral reef fishes

peer reviewe

Hearing capacities and otolith size in two ophidiiform species (<i>Ophidion rochei</i> and <i>Carapus acus</i>)

Numerous studies have highlighted the diversity of fish inner ear morphology. However, the function of the shape, size and orientation of the different structures remains poorly understood. The saccule (otolithic endorgan) is considered to be 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 a good structure with which 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 techniques. Carapus acus and O. rochei sagittae have similar maximal diameters; both species have larger otoliths than many non-ophidiiform species, especially compared with the intra-neurocranium volume. Both species are sensitive to sounds up to 2100 Hz. Relative to the skull, O. rochei has 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 species that need to execute precise and complex movements

Sound production in the clownfish Amphiprion clarkii

Although clownfish sounds were recorded as early as 1930, the mechanism of sound production has remained obscure. Yet, clownfish are prolific "singers" that produce a wide variety of sounds, described as "chirps" and "pops" in both reproductive and agonistic behavioral contexts. Here, we describe the sonic mechanism of the clownfish Amphiprion clarkii

Contribution to the study on sound production in clownfishes (Perciformes, Pomacentridae): a multidisciplinary approach

Clownfishes (Amphiprion spp.) are brightly colored fishes that are members of the Pomacentridae family. They are well known for their mutualistic relationship 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. Several studies have reported that vocalizations are associated with agonistic interactions but precise data are lacking and further investigations are needed. The nature of the sound-producing mechanisms also remained unresolved, only resting on few assumptions. Thereby, the main aim of the present thesis is (1) to determine the fundamental components of the acoustic communication in clownfishes, and (2) to explain the mechanisms of sound production. In order to achieve these objectives, the research has been divided into three different axes. Firstly, the study of the acoustic behaviors shows that no acoustic signal is associated with reproductive activities in clownfishes. Sound recordings during agonistic interactions indicate that these fishes produce two types of sounds. Aggressive sounds are produced during chases and threat displays while submissive (or head shaking) sounds are emitted in reaction to aggressive acts by dominant. Both types of sounds show size-related intraspecific differences in dominant frequency and pulse duration: smaller individuals produce higher frequency and shorter duration pulses than larger individuals, and inversely. Consequently, these sonic features might be useful cues for individual recognition and maintenance of cohesion within the group. Secondly, the study of the sound-producing mechanism highlights that aggressive sounds are initiated by buccal jaw teeth snapping caused by rapid mouth closure attributed to a sonic ligament. It appears that the swimbladder does not function as a resonator that amplifies and changes the quality of sounds. This structure is a highly damped sound source prevented from prolonged resonant vibrations. On the other hand, the rib cage might be the major acoustic radiator and its resonant properties might explain the size-related variations observed in pulse duration and dominant frequency. Thirdly, the comparison of aggressive sounds among fourteen clownfish species indicates that the same relationship between fish size and both dominant frequency and pulse duration is spread over the entire group (i.e. tribe Amphiprionini). These results highlight all species use a highly conservative mechanism of vocalization. Pulse period appears to be the most variable acoustic feature and could be involved in species-specific recognition, as well as pulse duration and dominant frequency in a lesser extent through their relationship with body size. Although sound production appears to be restricted to some agonistic behaviors, these sounds seem to constitute an integral part of the peculiar way of life of clownfishes. The aggressive and submissive sounds would also result from two different mechanisms.  Les poissons clowns (Amphiprion spp.), bien connus pour leur relation de mutualisme avec les anémones de mer, font partie de la famille des Pomacentridae. Ces poissons vivent en groupes hiérarchisés sur la base de la taille. Dans cette structure sociale impliquant le respect de la hiérarchie et de la territorialité, les interactions agonistiques sont nombreuses et ont pour but de maintenir des différences de tailles entre les individus de rang adjacent. Plusieurs études ont indiqué la présence de sons au cours des interactions agonistiques mais celles-ci souffrent d’un manque de caractérisation et des investigations plus poussées s’avèrent nécessaires. Seules quelques hypothèses du mécanisme producteur de sons ont été formulées, mais jamais vérifiées. Ainsi, la présente thèse vise à (1) étudier les composantes fondamentales de la communication acoustique chez les poissons clowns, et (2) comprendre les mécanismes de production de sons. Afin de répondre à ces objectifs, la recherche a été divisée en trois volets principaux. Premièrement, l’étude des comportements acoustiques montre qu’aucun son n’est associé aux différentes activités liées à la reproduction chez les poissons clowns. Les enregistrements au cours des interactions agonistiques indiquent que ces poissons produisent deux types de sons. Les sons d’agression sont émis durant les poursuites et autres comportements de menace alors que les sons de soumission sont produits en réponse à une agression de la part d’un dominant. Ces deux types de sons montrent des variations intraspécifiques liées à la taille : les petits individus produisent des pulsations de courtes durées associées à des fréquences élevées, et inversement. Par conséquent, ces caractéristiques acoustiques pourraient être des signaux utiles dans la reconnaissance de l’individu et le maintien de la cohésion au sein du groupe. Deuxièmement, l’étude du mécanisme de production des sons d’agression montre qu’ils résultent du claquement des dents portées par les mâchoires buccales suite à la fermeture rapide de la bouche produite par l’action d’un ligament sonique. Il apparaît que la vessie natatoire ne fonctionne pas comme un résonateur qui amplifie et change la qualité des sons. Cette structure est une source sonore hautement amortie et dépourvue de vibrations prolongées. En revanche, la cage thoracique pourrait être le principal radiateur acoustique et ses propriétés résonantes pourraient expliquer les variations liées à la taille observées dans la durée et la fréquence des pulsations. Troisièmement, la comparaison des sons d’agression entre 14 espèces de poissons clowns indique que la même relation entre la taille du poisson et la fréquence dominante ainsi qu’entre la taille et la durée des pulsations s’applique à l’ensemble du groupe (i.e. la tribu des Amphiprionini). Ces résultats révèlent que les espèces utilisent toutes un mécanisme très conservé. La période des pulsations semble être la caractéristique acoustique majeure pour l’identification des espèces. La durée des pulsations et la fréquence dominante seraient également impliquées en raison de leurs variations liées à la taille. Bien que la production de sons ne soit associée qu’à quelques comportements agonistiques, les sons semblent être indispensable au mode de vie particulier des poissons clowns. En outre, ces sons d’agression et de soumission résulteraient de deux mécanismes différents

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

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. 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. 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

Symbiotic relationship between the carapid fish <i>Onuxodon fowleri</i> (Ophidiiformes: Carapidae) and the pearl oyster <i>Pinctada margaritifera</i> (Mollusca: Bivalvia: Pteriidae)

At Makemo Atoll (French Polynesia), the carapid fish Onuxodon fowleri lives in symbiosis with the black-lip pearl oyster Pinctada margaritifera. Although the symbiont seems to live inside its host bivalve by using it as a shelter, additional data are still needed to better understand the exact nature of this association. For this purpose, we implemented an approach using stable isotope ratios of carbon (13C/12C) and nitrogen (15N/14N). The δ13C and δ15N values were measured in tissues of the pearl oyster (gonads, gills, mantle and muscles), white muscle tissue from the fish and other food sources. This stable isotope approach was also complemented by the analysis of stomach contents in the carapid fish. Overall, the isotopic compositions measured in the present study support a commensal relationship between O. fowleri and P. margaritifera. In addition, our isotopic data bring new information about another guest living inside P. margaritifera, namely the palaemonid shrimp Conchodytes meleagrinae. Based on the δ13C and δ15N values, it appears that the shrimp might feed on the bivalve gonads

The feasibility, acceptability and effectiveness of a feedback-informed group treatment (FIGT) tool for patients with anxiety or depressive disorders

Stress and Psychopatholog