Most studies of fish sounds show that the sounds are species-specific, with unique spectral and timing characteristics. This raises the question as to whether these sounds can be used to understand phyletic relationships between species and which acoustic parameters are subject to variation between species. In the present study, 597 sounds (and 2540 pulses) related to signal jumps of four Dascyllus species (Dascyllus aruanus, Dascyllus trimaculatus, Dascyllus albisella, and Dascyllus flavicaudus) from different geographic regions (Madagascar, Moorea, Rangiroa, and Hawaii) were analysed. It was possible to discern species-specific sounds, but also variation in sounds between populations. Large variations in sound length were found between Dascyllus species, whereas differences in interpulse duration were found to be variable between populations. In the regions where species live in sympatry, it appears that they restrict the variability in their sounds. This could comprise evidence of adaptation with character displacement of sonic characteristics where different species co-occur. However, sonic characteristics still overlapped substantially between species, suggesting that females would need to sample more than one sound and potentially use other cues to discriminate between species.

Animals use sensory stimuli to assess and select habitats, mates, and food as well as to communicate with other individuals. One of the great mysteries of crustacean ecology is how postlarvae locate the relatively rare patches of coral reef habitat on which they settle. The present study aimed to estimate, by experiments in aquaria and biochemical analysis, the sensory modalities of crustacean postlarvae for senses used in searching for their species' settlement habitat. The study was carried out on 9 crustacean species (Calappa calappa, Pachygrapsus planifrons, Xanthidae sp., Lysiosquillina maculata, L. sulcata, Raoulserenea sp., Stenopus hispidus, Palaemonidae sp., and Panulirus penicillatus). For each species, a cohort of 30 postlarvae was captured on the same night on the reef crest of Rangiroa Atoll (French Polynesia). Among the 9 crustacean species studied, 6 made active habitat choices among the 4 habitats tested (live coral, dead coral, macroalgae, and sand) at the postlarval stage, but the presence or absence of conspecifics on the habitat did not influence their selective choice. Sensory experiments found that 4 species differentiated between their preferred habitat versus another habitat and 2 species differentiated between conspecifics and heterospecifics, using visual and/ or olfactory cues. Lastly, the high performance liquid chromatography experiments showed that the 4 habitats and conspecifics (except L. maculata and S. hispidus) tested have different and unique chemical odors. Overall, our study is the first to highlight the sensory modalities for a broad range of crustacean species to detect and move toward settlement habitats and/or conspecifics.

BackgroundHolocentrids (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.ResultsIn 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.ConclusionThis 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.

SUMMARY 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.

Animals use sensory stimuli either to assess and select habitats, mates or food, as well as for communication. The present study aimed to understand the behavioural processes enabling several Chaetodon species (butterflyfishes) to locate one of their food sources (epibionts present on pearl oyster shells) at Rangiroa atoll (French Polynesia). Among the five species tested, our 2-channel choice flume chamber experiments identified three species that were attracted to their food source by chemical stimuli. HPLC experiments showed that pearl oysters and epibionts have specific and unique chemical fingerprints, either one or nine specific peaks, respectively. Overall, chemical stimuli are emitted by both epibionts (used directly by Chaetodon auriga, C. lunula and C. citrinellus) and live pearl oysters (used indirectly by C. auriga and C. lunula) to locate their food source. Biosynthesis of these chemical stimuli could be used to artificially attract butterflyfishes to pearl oyster rearing stations in order to increase the natural cleaning of pearl oyster shells and thus reduce one large cost for this aquaculture.