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

peer reviewe

Identification and role of sonic mediators in colonisation and settelment of fishes from corallous environments

La majorité des poissons de récifs coralliens présentent un cycle de vie complexe, caractérisé par une phase larvaire pélagique dispersive en milieu océanique, suivie d’une phase benthique au sein du lagon ou sur la pente externe du récif. Ce travail porte sur l'influence du stimulus sonore lors de la colonisation et de l'installation, au sein du récif, des larves de poissons. De récentes études ont montré un effet attracteur du son de récifs sur les larves de poissons et de crustacés. Mais on ignore encore la distance à laquelle les larves sont capables de repérer le son du récif, ni si elles sont attirées par une signature spectrale complexe ou plus simplement par la présence d'un "bruit". Enfin, on ignore si les différents habitats d’un récif peuvent présenter des signatures acoustiques propres, ni si les sons des habitats peuvent guider les larves lors de leur installation au sein du récif. L'étude de mesures de pression sonore le long de trois transects de 2 km effectuées sur la côte nord de l'île de Moorea (Polynésie Française) met en évidence une diminution régulière de l'intensité sonore jusqu'à une distance à la crête de 750-1000 m. Au-delà de cette distance, et jusqu'à 2 km, une augmentation graduelle de la pression sonore est observée. Dès lors, une larve située à 750-1000 m du récif se retrouve confrontée à deux gradients de pression, l'un dirigés vers l'océan et l'autre vers le récif, et devra faire appel à d'autres stimuli pour s'orienter vers ce dernier. Au sein du récif, les sons provenant de 5 habitats de Moorea (crête interne, récif barrière, récif frangeant, chenal et mangrove) ont été étudiés. Les signatures sonores de chaque habitat (hormis crête interne et récif barrière) diffèrent des autres sur une certaine gamme de fréquences, et ces différences sont conservées avec la distance (plusieurs km). De plus, l'étude de l'influence des sons d'habitats et d'un son artificiel sur le comportement des larves met en évidence une modification du comportement chez 16 des 20 espèces testées. Les différentes réponses illustrent deux stratégies d'installation sur base du son: soit une sélection directe de l'habitat, soit un évitement de certains habitats, et donc une sélection "par défaut" des habitats restants. Pourtant, les niveaux de pression sonore des habitats du lagon sont sous les seuils de capacités sonores des juvéniles d'Abudefduf vaigiensis, Acanthurus triostegus, Chaetodon citrinellus, Rhinecanthus aculeatus et Myripristis kuntee. Ce paradoxe nous pousse à remettre en question l'utilisation de l'outil "ABR" (Auditory Brainstem Response) dans les études de perception et d'influence des sons sur le comportement des poissons

Temporal and spatial comparisons of underwater sound signatures of different reef habitats in Moorea Island, French Polynesia

International audienceAs environmental sounds are used by larval fish and crustaceans to locate and orientate towards habitat during settlement, variations in the acoustic signature produced by habitats could provide valuable information about habitat quality, helping larvae to differentiate between potential settlement sites. However, very little is known about how acoustic signatures differ between proximate habitats. This study described within-and between-site differences in the sound spectra of five contiguous habitats at Moorea Island, French Polynesia: the inner reef crest, the barrier reef, the fringing reef, a pass and a coastal mangrove forest. Habitats with coral (inner, barrier and fringing reefs) were characterized by a similar sound spectrum with average intensities ranging from 70 to 78 dB re 1μPa.Hz-1. Th

Boat noise disrupts orientation behaviour in a coral reef fish

ArticleCoral reef fish larvae use sound to find suitable habitat during their vital settlement stage. Yet boat noise, which can cause stress and avoidance behaviour, and may cause masking via reduction of perceptual space, is common around coral islands and continental shelf habitats due to boat activity associated with fishing, tourism and transport of passengers and cargo. In a choice chamber experiment with settlement-stage coral reef fish larvae of the species Apogon doryssa, the directional responses of larvae were tested to 5 different noise types: Reef, Reef+Boat, Ocean, Ocean+Boat and White noise. The results showed that 69% of fish swam towards Reef playback compared with only 56% during Reef+Boat playback, while 44% of fish larvae moved away from Reef+Boat playback compared to only 8% during Reef playback. Significant directional responses were not observed during White noise, Ocean noise or Ocean+Boat noise playback. Overall, this study suggests that anthropogenic noise could have a disruptive effect on the response of fish larvae to natural reef sound, with implications for settlement and population dynamics in coral reef habitats disturbed by boat traffic.DefraNER

The influence of various reef sounds on coral-fish larvae behaviour

International audienceThe swimming behaviour of coral-reef fish larvae from 20 species of 10 different families was tested under natural and artificial sound conditions. Underwater sounds from reef habitats (barrier reef, fringing reef and mangrove) as well as a white noise were broadcasted in a choice chamber experiment. Sixteen of the 20 species tested significantly reacted to at least one of the habitat playback conditions, and a range of responses was observed: fishes were (1) attracted by a single sound but repelled by none (e.g. white-banded triggerfish Rhinecanthus aculeatus was attracted by the barrier-reef sound), (2) repelled by one or more sounds but attracted by none (e.g. bridled cardinalfish Pristiapogon fraenatus was repelled by the mangrove and the bay sounds), (3) attracted by all sounds (e.g. striated surgeonfish Ctenochaetus striatus), (4) attracted and repelled by several sounds (e.g. whitetail dascyllus Dascyllus aruanus was attracted by the barrier-reef sound and repelled by the mangrove sound) and (5) not influenced by any sound (e.g. convict surgeonfish Acanthurus triostegus). Overall, these results highlight two settlement strategies: a direct selection of habitats using sound (45% of the species), or a by-default selection by avoidance of certain sound habitats (35%). These results also clearly demonstrated the need to analyse the influence of sounds at the species-specific level since congeneric and confamilial species can express different behaviours when exposed to the same sounds

Genetic spectrum of hereditary neuropathies with onset in the first year of life

Early onset hereditary motor and sensory neuropathies are rare disorders encompassing congenital hypomyelinating neuropathy with disease onset in the direct post-natal period and Dejerine-Sottas neuropathy starting in infancy. The clinical spectrum, however, reaches beyond the boundaries of these two historically defined disease entities. De novo dominant mutations in PMP22, MPZ and EGR2 are known to be a typical cause of very early onset hereditary neuropathies. In addition, mutations in several other dominant and recessive genes for Charcot-Marie-Tooth disease may lead to similar phenotypes. To estimate mutation frequencies and to gain detailed insights into the genetic and phenotypic heterogeneity of early onset hereditary neuropathies, we selected a heterogeneous cohort of 77 unrelated patients who presented with symptoms of peripheral neuropathy within the first year of life. The majority of these patients were isolated in their family. We performed systematic mutation screening by means of direct sequencing of the coding regions of 11 genes: MFN2, PMP22, MPZ, EGR2, GDAP1, NEFL, FGD4, MTMR2, PRX, SBF2 and SH3TC2. In addition, screening for the Charcot-Marie-Tooth type 1A duplication on chromosome 17p11.2-12 was performed. In 35 patients (45%), mutations were identified. Mutations in MPZ, PMP22 and EGR2 were found most frequently in patients presenting with early hypotonia and breathing difficulties. The recessive genes FGD4, PRX, MTMR2, SBF2, SH3TC2 and GDAP1 were mutated in patients presenting with early foot deformities and variable delay in motor milestones after an uneventful neonatal period. Several patients displaying congenital foot deformities but an otherwise normal early development carried the Charcot-Marie-Tooth type 1A duplication. This study clearly illustrates the genetic heterogeneity underlying hereditary neuropathies with infantile onset