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

in Journal of Fish Biology (2009), 75

Sound production in four damselfish (Dascyllus) species: phyletic relationships?

in Biological Journal of the Linnean Society (2009), 97

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 ... [more ▼]

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. [less ▲]

Ontogenetic determinism of colour polymorphism in a coral reef fish, Chrysiptera brownriggii (Pomacentridae)

Poster (2008, October)

The determinism of ontogenetic colour changes induced by environmental factors is poorly understood in marine fishes, especially in coral ecosystems. The present study, conducted at the Rangiroa Atoll ... [more ▼]

The determinism of ontogenetic colour changes induced by environmental factors is poorly understood in marine fishes, especially in coral ecosystems. The present study, conducted at the Rangiroa Atoll (French Polynesia) explored the effects of fish density and brightness/darkness condition (type of background) on colour determination during the ontogeny of a territorial damselfish Chrysiptera brownriggii (Bennett 1828). In this species, larvae always colonize the reef (settlement) in a yellow morph, while juveniles and adults can display two distinct colour-patterns: yellow and dark brown. Our experiments in aquaria showed that a significant higher proportion of C. brownriggii larvae turned into the brown morph in a dark condition during a period of 5 and 15 days (70-100% of brown morph induction) just after reef settlement. A significant positive effect of fish density inducing a brown colour morph was also highlighted. After a first colour induction, reversibility experiments illustrated that juveniles can change their colour morph anew after a 5-day period. Although a shift from brown to yellow morph seemed to be more limited. In the dark condition, yellow adults did not change their colour after a 5-day period. Our results showed that the colour dimorphism in C. brownriggii should be density-dependent. The period of sensitivity seems to last throughout the post-settlement period. We suggest that the yellow morph in C. brownriggii can be viewed as a paedomorphic trait. Overall, our results reveal that a darkness/lightness environment and fish density are environmental cues related to colour determinism in the polyphenetic C. brownriggii. [less ▲]

Agonistic sounds in the skunk clownfish (Amphiprion akallopisos) : spectral and temporal basis for fish size assessment and individual recognition

Poster (2008)

Clownfishes (i.e. Amphiprion akallopisos) are territorial fishes that use sound production to defend their anemone territory. They live in social groups within which there is a size-based dominance ... [more ▼]

Clownfishes (i.e. Amphiprion akallopisos) are territorial fishes that use sound production to defend their anemone territory. They live in social groups within which there is a size-based dominance hierarchy. In such a system, agonistic interactions are usual and play an important role in social organization by maintaining size differences between individuals adjacent in rank. Sounds are known to be used in agonistic interactions; they could therefore be associated with aggressive display within the group hierarchy. In the present study, we compared the sonic characteristics between individuals of different sizes and of different sexual status (non-breeder, male and female). Sound analysis revealed that dominant frequency and pulse length are highly correlated with fish size, and are not related to sex. No information related to size can be extracted from the pulse period, interpulse duration and number of pulses per train. Evidence is provided that dominant frequency and pulse length are morphologically determined signals related to fish size. In that case, smaller individuals produce shorter duration and higher frequency sounds than larger individuals. Both sonic features are signals conveying information related to the size of the emitter. This finding could be of significant importance, and might help to understand one of the mechanisms that carry the clue for individual recognition within the group hierarchy. [less ▲]

Ontogenetic shape changes in Pomacentridae (Teleostei, Perciformes) and their relationships with feeding strategies: a geometric morphometric approach

in Biological Journal of the Linnean Society (2008), 95

The present study explores the shape changes of cranial structures directly involved in food capturing during growth after reef settlement in two species of Pomacentridae (Dascyllus aruanus and ... [more ▼]

The present study explores the shape changes of cranial structures directly involved in food capturing during growth after reef settlement in two species of Pomacentridae (Dascyllus aruanus and Pomacentrus pavo). Landmark-based geometric morphometrics were used to study allometric patterns and related shape changes in four skeletal units: neurocranium, suspensorium and opercle, mandible and premaxilla. At settlement, the larvae of both species have a relatively similar morphology, especially with respect to the mandible. Their shapes suggest a feeding mode defined as ram/suction-feeding. Ontogenetic shape changes show a shift to a suction feeding mode of prey capture. The main transformations involved are an increase in height of the suspensorium and the opercle, an elevation of the supraoccipital crest, a relative shortening of the mandible, and a lengthening of the ascending process of the premaxilla. Shape changes of the mandible in the two studied species also reflect an increase of biting capacities. The high disparity between adult shape results from differences in the rate and in the length of ontogenetic trajectories, from divergence of the ontogenetic trajectories (neurocranium, mandible, and premaxilla) and parallel shifts of the trajectories in the size-shape space (suspensorium and opercle). In an evolutionary context, allometric heterochronies during ontogeny of different skeletal unit of the head may be considered as a basis for the explanation of the diversity of damselfishes. [less ▲]

Sound production in the clownfish Amphiprion clarkii

in Science (2007), 316(5827), 1006-1006

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 ... [more ▼]

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. [less ▲]

Diet of Damselfishes (Pomacentridae): a multidisciplinary approach

Poster (2006, October)

Coral reefs are the marine ecosystem showing the greatest fish diversity. Damselfishes (Pomacentridae) represent, with more than 340 species, one of the most important families in the coral reef ... [more ▼]

Coral reefs are the marine ecosystem showing the greatest fish diversity. Damselfishes (Pomacentridae) represent, with more than 340 species, one of the most important families in the coral reef environment. Currently their diet is understudied. This work has 2 aims: (i) to characterize the diet of 13 pomacentrid species of the reef of Toliara (Madagascar) and (ii) to investigate if the specific diversity of this family would result from a strong trophic segregation. A multidisciplinary approach including morphological data (teeth, lower jaw-lever mechanics and intestine length), stomach contents and stable isotope analysis were used. The morphological approach and the stomach contents show that each studied species is able to capture small planktonic preys (e.g. copepods). However, the 13 species can be divided into two trophic guilds: alguivores and planktivores (respectively species where the filamentous algae and the planktonic preys count for more than 60% of their diet). Within these two principal classes, the analysis of the stomach contents and stable isotopes permit to define sub-groups : (1) the species having a food behaviour exclusively alguivore or planktivore (> 90% of their diet) (2) species showing a more varied diet by also eating other types of preys such as vagiles and/or sessiles invertebrates. The diet would contribute but could not explain all diversity in Pomacentridae. Some species show a very similar diet. Consequently other ecological factors should be responsible for the reduction of interspecific competitions and for the existence of such diversity. [less ▲]

Diversification among damselfishes (Pomacentridae): a comparison of ontogenetic trajectories

Poster (2006, August)

The Pomacentridae family, or damselfishes, includes more than 330 species living mainly in a coral reef environment. They have a complex life cycle involving a pelagic dispersion period of larvae and a ... [more ▼]

The Pomacentridae family, or damselfishes, includes more than 330 species living mainly in a coral reef environment. They have a complex life cycle involving a pelagic dispersion period of larvae and a juvenile and adult benthic life period associated to reef. The colonisation is associated with a metamorphosis allowing the fish to adapt to their new environment. Our study focused on morphological modifications, as skeletal shape changes, occurring during the development from settling larvae to juvenile and leading to diversification of adult species. To test allometry and to examine diversification in shapes, geometric morphometrics were used. This method, which allows description and statistical analysis of form, is applied to define ontogenetic shape changes and to compare allometries responsible for species diversification. It is applied here for skull structures involved in food capture as neurocranium, suspensorium, opercle, premaxillary bone and mandible. Six species were studied: Chromis viridis, Dascyllus aruanus, Dascyllus carneus, Pomacentrus pavo, Chrysiptera glauca and Stegastes nigricans. At the end of larval stage, structures in fishes are rather similar. None of the species has an isometric growth. Ontogenetic allometries concern each skeletal unit. The two species of Dascyllus are the lone to have a common ontogenetic transformation, and it appears that allometries giving the shapes’diversification correspond to ecological adaptations of each species. From a functional point of view, the general trend in skeletal shape changes corresponds to an optimisation of the suction feeding apparatus (for example: development in height and length of the suspensorium and opercle, shortening of the mandible). [less ▲]

Changement de forme ontogénétique des structures céphaliques chez les Pomacentridae : une approche par la morphométrie géométrique

Poster (2006, March)

Les Pomacentridae (Damselfishes), comme la plupart des poissons des récifs coralliens, possèdent un cycle de vie complexe comprenant une phase larvaire pélagique dispersive, et une phase juvénile et ... [more ▼]

Les Pomacentridae (Damselfishes), comme la plupart des poissons des récifs coralliens, possèdent un cycle de vie complexe comprenant une phase larvaire pélagique dispersive, et une phase juvénile et adulte benthique associée au milieu corallien. Le passage du stade larvaire au stade juvénile se fait au cours d’un véritable processus de métamorphose qui généralement coïncide avec la colonisation du récif. Cette transition est une phase cruciale impliquant un changement du mode de vie qui peut s’accompagner de modifications morphologiques. A l’heure actuelle, peu d’information existe sur ce qui caractérise la métamorphose des poissons récifaux d’un point de vue squelettique et leurs implications fonctionnelles. Celle-ci n’est principalement décrite que par des changements de pigmentation et des changements morphologiques telles que des modifications de proportions du corps. L’objectif de cette étude est de caractériser les changements de forme des structures céphaliques directement impliquées dans la prise de nourriture chez deux espèces de Pomacentridae : Pomacentrus pavo (Bloch, 1787) et Dascyllus aruanus (Linnaeus, 1758). Dans cette étude, la morphométrie géométrique basée sur la méthode des points repères est utilisée pour décrire les trajectoires de croissance et les changements de forme caractérisant les pièces squelettiques durant la période de colonisation du récif. Cette analyse est appliquée aux quatre unités fonctionnelles suivantes : le neurocrâne, l’ensemble « suspensorium et opercule », la mandibule et le prémaxillaire. Celles-ci sont étudiées en vue latérale. Les patrons de transformations de chaque structure durant le développement sont décrits morphologiquement au moyen de grilles de déformation. Les modifications morphologiques observées chez P. pavo et D. aruanus durant le développement vont dans le sens d’une amélioration du système de prise de nourriture par aspiration. Les principaux changements sont : un agrandissement en hauteur et en largeur du suspensorium et de l’opercule, une élévation de la crête supraoccipitale, un déplacement vers l’avant de l’articulation mandibulaire, un raccourcissement de la mandibule et un allongement du processus ascendant du prémaxillaire. Ces transformations au niveau de la tête pourraient refléter un changement de mode de prise de nourriture au cours de l’ontogénie. La comparaison des unités fonctionnelles entre les deux espèces à l’état larvaire révèle que certaines unités (mandibule par exemple) sont très similaires dans leur forme tandis que d’autres (neurocrâne, unité « suspensorium et opercule » et le prémaxillaire) présentent une forme déjà dissemblable. Cependant, la similarité observée laisse clairement supposer que ces pièces sont sujettes aux mêmes contraintes de prise de nourriture : leurs formes permettraient de les considérer comme des « ram-feeders » se nourrissant du même type de proie. Au cours de leur croissance et de la colonisation du récif, la différenciation des entités squelettiques entre chaque espèce se renforce, permettant ainsi à chacune de s’installer progressivement dans sa niche écologique. Les différences entre les larves et les adultes paraissent liées au moins aux contraintes écologiques. [less ▲]

Comparison of the skull development in Damselfish (Pomacentridae): an ecomorphological approach

Poster (2001, November)