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International audience

International audience

International audience

International audience; The ability to produce sounds foracoustic communication is known indifferentBalistidaespeciesbuttheeventualsynapomorphicaspectofthe mechanism remains to be shown. In Rhinecanthus aculeatus,soundsresultfromalternatesweepingmovementsoftheright andleftpectoral fins, which push a system of three scutes against the swimbladder wall. In this study, we made a comparison between thesounds produced by this species and two additional ones (Balistapusundulatus and Rhinecanthus rectangulus) using hand-heldspecimens to provide a description of the sound mechanism. Theresults highlighted that the sound production mechanism is similar inthe three species. According to recent phylogenetic data and sharedmorphological features, this mechanism could be common to themajority of Balistidae family members and all species could becapable of sound production using pectoral fins.

Glass eels were sampled in two estuaries of French Polynesia (Tahiti and Moorea islands) from 2009 to 2017. Three species were identified by morphological measurements (Anguilla marmorata, A. megastoma and A. obscura). Our results revealed a difference in the species composition between Moorea and Tahiti. The recruitment of eels is seasonal and occurs between November and March during the rainy season, with peaks in December and January. The recruitment size of glass eels was analyzed for the three species. We found a difference between the sizes at recruitment between Tahiti and Moorea. Overall, using a negative binomial GLM, we show that rainfalls, waves’ direction, light and temperature were key factors for glass eel recruitment in French Polynesia.

Elasmobranchs are critical to tourism industries worldwide. In French Polynesia, where ecotourism is the second most important industry, little is known about the spatiotemporal distribution of eagle rays. This study represents the first investigation into habitat use and behaviour of ocellated eagle rays (Aetobatus ocellatus) in French Polynesia focused on two sites with different levels of anthropogenic noise. Environmental variables and biological data were recorded over a one-year period to explore the distribution patterns of 113 eagle rays identified at these sites. Results revealed distinct patterns in habitat use between the two sites, with the eagle ray population structured according to ontogenetic stage. Young rays preferred the site with lower levels of noise pollution, where they foraged at the end of the day. Adult eagle rays gathered in the mornings at the louder site, where the only noticeable activity was group swimming. Overall, our results could help conservation initiatives to manage this important species in French Polynesia, and potentially other coral reef areas, especially in the context of rising human impacts on the environment.

Various species of fish are known to produce sounds in different social contexts suggesting an important communicative role of acoustic signals. The aim of this thesis is to study the structure and the function of sounds produced during aggressive interactions between males of the cichlid fish Metriaclima zebra. By means of playback experiments, the relative role of acoustic and visual cues during agonistic interactions is evaluated. The results show that aggressive behaviour is essentially based on visual stimuli. Acoustic stimuli alone never trigger aggression but modulate males' behavior by decreasing the high level of aggressiveness found when only the visual channel is present. A fine analysis of the structure of sounds produced during disputes shows that signals emitted by M. zebra encode information related to the size of the emitter. The individual signature remains poorly defined. In order to understand the decoding process of information by receivers, I set up a paradigm allowing to show that territorial males increase their territorial activity and approach loudspeakers in response to playbacks. Playback experiments using signals with artificially modified acoustic parameters suggest a large tolerance for temporal variations. This thesis thus participates to the comprehension of the biological function of acoustic communication in a fish. It calls for further studies concerning the transmitted information and its encoding process, De nombreuses espèces de poissons sont connues pour produire des sons dans différents contextes sociaux suggérant un rôle important des signaux acoustiques dans la communication. L'objectif de cette thèse est d'étudier la structure et la fonction des sons produits lors d'interactions agressives entre mâles chez le poisson cichlidé Metriaclima zebra. Grâce à des expériences de playback, le rôle relatif des indices acoustiques et visuels lors des interactions agonistiques est évalué. Les résultats montrent que les comportements agressifs reposent essentiellement sur des stimuli visuels. Les stimuli acoustiques seuls ne déclenchent jamais d'agression mais modulent le comportement des mâles en diminuant le niveau élevé d'agressivité observé lorsque le canal visuel est seul présent. Une analyse fine de la structure acoustique des sons produits pendant des conflits montre que les signaux émis par M. zebra codent des informations relatives à la taille de l'individu émetteur. La signature individuelle reste assez mal définie. Pour comprendre le décodage de l'information au niveau du poisson récepteur, j'ai mis au point un protocole de test permettant de constater que des mâles territoriaux augmentent leur activité territoriale et approchent le haut-parleur en réponse aux playbacks. Des expériences de playback utilisant des signaux aux paramètres acoustiques artificiellement modifiés suggèrent une grande tolérance des individus envers les variations temporelles. Cette thèse participe ainsi à la compréhension de la fonction biologique de la communication acoustique chez un poisson. Elle appelle de nouvelles études concernant les informations transmises et leur codage

International audience; Acoustic signals are produced in many fish species during agonistic or courtship interactions. A way to test the biological role of these sounds is the use of acoustic playback experiments. However, sounds are usually associated with visual displays and playback experiments performed in fish so far, often failed to match acoustic and visual stimuli. To avoid this mismatch issue, we experimentally separated or coupled visual and acoustic channels to test the role of sounds produced during male–male aggressive interactions in a cichlid fish, Metriaclima zebra. Results show that aggressive behaviour is based on visual stimuli and that acoustic signals alone never trigger aggression. Furthermore, the association between visual and acoustic channels lowers the level of aggressiveness found when fish can only interact visually. This suggests that acoustic signals used during a dispute may complement visual displays to modulate males’ behaviour by reducing their aggressiveness and the risk of escalated fights.

Interactions and communication between individuals occur in a complex social environment in which senders and receivers are able to adjust their behaviour according to the context. Watching fights between others acts on a bystander’s motivation to engage in a fight and may make it behave more aggressively during subsequent disputes. This phenomenon is known as aggressive priming. The aim of our study was to investigate if this priming response follows a step function, i.e. appears only above a threshold level of aggression witnessed by a bystander. We found that bystanders behaved more aggressively in subsequent interactions when pre-exposed to an aggressive conspecific that was engaged in a fight whatever the level of aggression this fight reached. However, bystanders’ behaviour after pre-exposure was not correlated to the previously witnessed level of aggressiveness. These results suggest that individuals alter their behaviour in an aggressive social environment and indicate that priming effect follows a step function where aggression is triggered by an aggressive context. We discuss our results and the effect of pre-exposure on agonistic interactions in a communication network perspective.

Peer reviewed: True, Funder: Alexander von Humboldt-Stiftung; Id: http://dx.doi.org/10.13039/100005156, In 2020, the COVID-19 pandemic led to a reduction in human activities and restriction of all but essential movement for much of the world's population. A large, but temporary, increase in air and water quality followed, and there have been several reports of animal populations moving into new areas. Extending on long-term monitoring efforts, we examined how coral reef fish populations were affected by the government-mandated lockdown across a series of Marine Protected Area (MPA) and non-Marine Protected Area (nMPA) sites around Moorea, French Polynesia. During the first six-week lockdown that Moorea experienced between March and May 2020, increases (approx. two-fold) in both harvested and non-harvested fishes were observed across the MPA and nMPA inner barrier reef sites, while no differences were observed across the outer barrier sites. Interviews with local amateur and professional fishers indicated that while rules regarding MPA boundaries were generally followed, some subsistence fishing continued in spite of the lockdown, including within MPAs. As most recreational activities occur along the inner reef, our data suggest that the lockdown-induced reduction in recreational activities resulted in the recolonization of these areas by fishes, highlighting how fish behaviour and space use can rapidly change in our absence.