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See detailBipartite life cycle of coral reef fishes promotes increasing shape disparity of the head skeleton during ontogeny: an example from damselfishes (Pomacentridae)
Frederich, Bruno ULg; Vandewalle, Pierre ULg

in BMC Evolutionary Biology (2011), 11

Background: Quantitative studies of the variation of disparity during ontogeny exhibited by the radiation of coral reef fishes are lacking. Such studies dealing with the variation of disparity, i.e. the ... [more ▼]

Background: Quantitative studies of the variation of disparity during ontogeny exhibited by the radiation of coral reef fishes are lacking. Such studies dealing with the variation of disparity, i.e. the diversity of organic form, over ontogeny could be a first step in detecting evolutionary mechanisms in these fishes. The damselfishes (Pomacentridae) have a bipartite life-cycle, as do the majority of demersal coral reef fishes. During their pelagic dispersion phase, all larvae feed on planktonic prey. On the other hand, juveniles and adults associated with the coral reef environment show a higher diversity of diets. Using geometric morphometrics, we study the ontogenetic dynamic of shape disparity of different head skeletal units (neurocranium, suspensorium and opercle, mandible and premaxilla) in this fish family. We expected that larvae of different species might be relatively similar in shapes. Alternatively, specialization may become notable even in the juvenile and adult phase. Results: The disparity levels increase significantly throughout ontogeny for each skeletal unit. At settlement, all larval shapes are already species-specific. Damselfishes show high levels of ontogenetic allometry during their postsettlement growth. The divergence of allometric patterns largely explains the changes in patterns and levels of shape disparity over ontogeny. The rate of shape change and the length of ontogenetic trajectories seem to be less variable among species. We also show that the high levels of shape disparity at the adult stage are correlated to a higher level of ecological and functional diversity in this stage. Conclusion: Diversification throughout ontogeny of damselfishes results from the interaction among several developmental novelties enhancing disparity. The bipartite life-cycle of damselfishes exemplifies a case where the variation of environmental factors, i.e. the transition from the more homogeneous oceanic environment to the coral reef offering a wide range of feeding habits, promotes increasing shape disparity of the head skeleton over the ontogeny of fishes. [less ▲]

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See detailPatrones de evolución morfológica de la región cefálica en damiselas (Perciformes, Pomacentridae) del Pacífico Oriental
Aguilar-Medrano, Rosalia; Frederich, Bruno ULg; De Luna, Efrain et al

Conference (2010, October)

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See detailAnálisis ecomorfológico de la aleta pectoral en damiselas (Perciformes, Pomacentridae) del Pacífico Oriental
Aguilar-Medrano, Rosalia; Frederich, Bruno ULg; De Luna, Efrain et al

Poster (2010, October)

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See detailTrophic niche width, shift, and specialization of Dascyllus aruanus in Toliara lagoon, Madagascar
Frederich, Bruno ULg; Lehanse, Olivier; Vandewalle, Pierre ULg et al

in Copeia (2010), 2010(2), 218-226

Intrapopulation diet specializations may result from the use of different dietary items or foraging tactics by individuals within a single population. The damselfish, Dascyllus aruanus, is a highly site ... [more ▼]

Intrapopulation diet specializations may result from the use of different dietary items or foraging tactics by individuals within a single population. The damselfish, Dascyllus aruanus, is a highly site-attached coral reef fish living in size hierarchies among branched corals. The trophic niche width and feeding specialization of this species were explored using stable isotopes and stomach content analyses. Intra-group niche variation was mainly related to fish size. Within social groups, D. aruanus gradually shifted its foraging tactics according to size; smaller fish fed on benthic prey such as isopods and copepods, and the larger fish foraged in the water column on planktonic copepods and larger-sized prey. Group density was found to explain some variation in trophic niche characteristics; greater specialization on prey size was observed in the colony having the highest density. All members of the largest colony foraged more frequently in the water column. Knowing that planktonic copepods are more energy-rich than benthic ones, a positive group-size effect facilitating access to preferred prey is suggested. Group size and group density effects on trophic specialization did not have any impact on body condition, suggesting that the behavioral plasticity of D. aruanus in its foraging strategies permits compensation for the maintenance of body conditions. [less ▲]

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See detailEvolution of ontogenetic allometry shaping giant species: a case study from the damselfish genus Dascyllus (Pomacentridae)
Frederich, Bruno ULg; Sheets, David

in Biological Journal of the Linnean Society (2010), 99(1), 99-117

The evolution of body size, the paired phenomena of giantism and dwarfism, has long been studied by biologists and paleontologists. However, detailed investigations devoted to the study of the evolution ... [more ▼]

The evolution of body size, the paired phenomena of giantism and dwarfism, has long been studied by biologists and paleontologists. However, detailed investigations devoted to the study of the evolution of ontogenetic patterns shaping giant species are scarce. The damselfishes of the genus Dascyllus appear as an excellent model for such a study. Their well understood phylogeny reveals that large-bodied species have evolved in two different clades. Geometric morphometric methods were used to compare the ontogenetic trajectories of the neurocranium and the mandible in both small-bodied (Dascyllus aruanus and Dascyllus carneus; maximum size: 50–65 mm standard length) and giant (Dascyllus trimaculatus and Dascyllus flavicaudus; maximum size: 90–110 mm standard length) Dascyllus species. At their respective maximum body size, the neurocranium of the giant species is significantly shorter and have a higher supraoccipital crest relative to the small-bodied species, whereas mandible shape variation is more limited and is not related to the ‘giant’ trait. The hypothesis of ontogenetic scaling whereby the giant species evolved by extending the allometric trajectory of the small-bodied ones (i.e. hypermorphosis) is rejected. Instead, the allometric trajectories vary among species by lateral transpositions. The rate of shape changes and the type of lateral transposition also differ according to the skeletal unit among Dascyllus species. Differences seen between the two giant species in the present study demonstrate that giant species may appear by varied alterations of the ancestor allometric pattern. [less ▲]

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See detailEvidence of an original scale development during the settlement phase of a coral reef fish (Acanthurus triostegus)
Frederich, Bruno ULg; Lecchini, David; Vandewalle, Pierre ULg

in Journal of Applied Ichthyology (2010), 26

As the majority of coral reef fishes, the Convict Surgeonfish Acanthurus triostegus (Acanthuridae) has a complex life cycle that involves an ontogenetic change in morphology, physiology and behaviour as ... [more ▼]

As the majority of coral reef fishes, the Convict Surgeonfish Acanthurus triostegus (Acanthuridae) has a complex life cycle that involves an ontogenetic change in morphology, physiology and behaviour as its pelagic larval stage colonizes the benthic habitat. Few studies are devoted to the changes in skeleton during the settlement phase of coral reef fishes. In the present study, we highlighted an unexpected scales development in A. trisostegus just after the reef settlement. At settlement (t0), A. triostegus showed calcified and very thin vertical plates, lying in the dermis on the whole body. During the first 9 days after settlement, thin vertical plates regressed and adult scales began to appear simultaneously. At 12 days post-settlement, the whole body was covered with small scales. Overall, such a rapid skeletal transformation is an example of morphological changes dealing with metamorphosis of coral reef fishes. [less ▲]

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See detailColour differentiation in a coral reef fish throughout ontogeny: habitat background and flexibility
Frederich, Bruno ULg; Mills, Suzanne C.; Denoël, Mathieu ULg et al

in Aquatic Biology (2010), 9(3), 271-277

Colour polymorphism is widespread in animals but, in contrast to other types of polymorphism, has been little explored during ontogeny. Among coral reef fish, the surge damselfish Chrysiptera leucopoma ... [more ▼]

Colour polymorphism is widespread in animals but, in contrast to other types of polymorphism, has been little explored during ontogeny. Among coral reef fish, the surge damselfish Chrysiptera leucopoma settles in the larval stage as a yellow morph, whereas 2 colour morphs (yellow and brown) are apparent in adults at Rangiroa Atoll, French Polynesia. To understand this dimorphism, we tested, under controlled conditions, the hypotheses that: (1) environmental cues (habitat background and conspecific density) play important roles in morph differentiation during ontogeny and (2) morph colouration is reversible. Our first experiment showed that a dark habitat background induced the formation of the brown morph, while C. leucopoma larvae kept their yellow morph when placed in aquaria with a bright habitat background. Colour change from yellow to brown also occurred within the bright habitat, but only at high conspecific densities. Our second experiment showed that colour change was reversible within 15 d post-settlement, but not at the adult stage. Overall, our results highlighted that the studied polymorphism may be environmentally induced and reversible during the first post-settlement days of this coral reef fish. [less ▲]

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See detailEtude de la diversité trophique des poissons demoiselles (Perciformes, Pomacentridae) par l'examen des variations du squelette céphalique à partir de leur vie récifale
Frederich, Bruno ULg

Doctoral thesis (2009)

Damselfishes (Pomacentridae) are among the most speciose coral reef fishes (>350 species). They are abundant, constituting a large proportion of the individuals at small spatial scale. Despite this ... [more ▼]

Damselfishes (Pomacentridae) are among the most speciose coral reef fishes (>350 species). They are abundant, constituting a large proportion of the individuals at small spatial scale. Despite this importance, few studies deal with their trophic and morphological diversity. As most coral reef fishes, damselfishes have a complex life-cycle with two distinct phases: (1) a potentially dispersive pelagic larval phase and (2) a sedentary adult phase associated to the coral reef environment. The larval phase ends at reef settlement. The pelagic environment offers a relatively homogeneous habitat for all pomacentrids larvae which exclusively feed on planktonic copepods. On the other hand, the variety of resources is higher in the coral reef. During ontogeny, damselfishes undergo a change in their lifestyle that involves an ontogenetic change in morphology, physiology and behavior in order to maximize survival in each environment. This thesis aims to test the hypothesis that a higher trophic diversity at the adult stage corresponds to a higher disparity level (measure of morphological diversity of a clade) than in larvae. To answer this question, the research has been divided into three main axis. Firstly, the stable isotope (δ15N and δ13C) and stomach content analyses in thirteen sympatric species of damselfishes have highlighted three main groups according to their foraging strategies: (1) the pelagic feeders which feed on planktonic copepods, (2) the benthic feeders which are mainly herbivorous grazing filamentous algae and (3) an intermediate group including species which pick up their prey in the pelagic and the benthic compartment in variable proportions (e.g. planktonic and benthic copepods, small vagile invertebrates and filamentous algae). Only two species are known to be exclusively coral polyp feeders. Secondly, an ecomorphological study has characterized the diversity of the adults head skeleton. Shape variations of four skeletal units (neurocranium, suspensorium and opercle, mandible and premaxilla) were explored in fourteen species using landmark-based geometric morphometrics. The results reveal a parallelism between the morphological diversity and the trophic variety at the adult stage. Generally speaking, the planktivorous damselfishes show skeletal shapes enhancing suction feeding (e.g. high suspensoria and opercles, a large supraoccipital crest, short mandibles forming a small mouth) The herbivorous species (grazers) have shapes improving the robustness of some skeletal parts (e.g. high and robust mandibles, broad hyomandibular). Among the planktivorous species, Chromis viridis and C. acares show divergent shapes from the species of the same trophic guild. Their skeletal characteristics suggest they could be considered as ram-suction feeders. The buccal dentition is not highly related to the diet. Thirdly, the post-settlement ontogeny and the variation of shape disparity were studied and compared among eight species having varied diets. The post-settlement growth is highly allometric in all species (40 – 87% of shape variations). For each skeletal unit, the morphological disparity is higher at the adult stage compared with the settlement stage. All studied developmental parameters were affected by evolutionary changes. At settlement, the larval shapes are already species-specific, probably due to differences in pelagic larval duration among species. The increasing of shape disparity during ontogeny is mainly related to the divergence of allometric patterns. The length of ontogenetic trajectories and the developmental rates appear as less variable parameters. Generally speaking, no correlation exist between the phylogenetic or ecological (diet, pelagic larval duration,..) data and the developmental parameters. Species of the genus Dascyllus were studied in a particular context: a study case of giantism. The geometric morphometric methods show that the small species and the giant ones share the same ontogenetic trajectories for the neurocranium and the mandible. A part of their diversification should result from heterochronic processes. The cephalic larval shapes suggest a mode of prey capture defined as ram-suction feeding. In all studied species, the morphological transformations reveal an optimization of the suction feeding system. During growth, the main shape changes include a heightening of the suspensoria and the opercles, an elevation of the supraoccipital crest, a shortening of the mandibles and a lengthening of the ascending process of the premaxilla. In the benthic feeders, other shape changes are related to an improved biting and grazing abilities (e.g. mandibles and suspensorium appear more robust at the adult stage). [less ▲]

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See detailThe ontogenetic dynamic of skull shape disparity in damselfishes (Pomacentridae)
Frederich, Bruno ULg; Vandewalle, Pierre ULg

Conference (2009, May)

Damselfishes (Pomacentridae) are among the most speciose of coral-reef fishes, with > 350 species world-wide, most of which live on coral reefs. They have a life history with two distinct phases: a ... [more ▼]

Damselfishes (Pomacentridae) are among the most speciose of coral-reef fishes, with > 350 species world-wide, most of which live on coral reefs. They have a life history with two distinct phases: a dispersive pelagic larval phase and a sedentary benthic adult phase. The larval stage ends at coral reef settlement. All larvae feed on planktonic preys whereas juveniles and adults associated to the coral reef show a higher diversity of diets: zooplanktivorous, herbivorous, coral polyp feeders and omnivorous species. Morphological disparity is a major theme in paleobiology. Most studies of disparity have focused on its temporal dynamics over a geological time scale. Surprisingly, the relationship between ontogeny and disparity has received little attention. Using landmark-based geometric morphometrics, this study aims to test the hypothesis that the ontogenetic change in diet is related to an increase of shape disparity in head skeletal units (neurocranium, suspensorium + opercle, mandible and premaxilla) during the post-settlement growth in eight species of damselfishes. At the end of the larval stage (coral reef settlement), all skeletal units are already species-specific. By comparing levels of shape disparity between species at three developmental stages (at settlement, at 60 mm SL and at maximum adult body size), we found that disparity increases significantly during ontogeny. The ontogenies of shape were also compared to identify evolutionary changes in developmental processes modifying shape disparity. The ontogenetic patterns are highly divergent among species. At least, evolutionary changes affected three parameters of ontogenetic trajectories of shape in this group: (1) the allometric patterns (the direction in which the vector representing the ontogeny of shape point), (2) the amount of change undergone during the post-settlement phase and (3) the rate of shape changes. From a functional point of view, the ontogenetic transformations enhance suction-feeding and/or algae scraping (e.g. heightening of the suspensorium and opercle, shortening of the mandible). [less ▲]

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See detailEvidence of an atypical scale development during the settlement phase of a coral reef fish
Frederich, Bruno ULg; Lecchini, David; Vandewalle, Pierre ULg

Poster (2009, April)

As the majority of coral reef fishes, the Convict Surgeonfish Acanthurus triostegus (Acanthuridae) has a complex life cycle that involves an ontogenetic change in morphology, physiology and behaviour as ... [more ▼]

As the majority of coral reef fishes, the Convict Surgeonfish Acanthurus triostegus (Acanthuridae) has a complex life cycle that involves an ontogenetic change in morphology, physiology and behaviour as its pelagic larval stage colonizes the benthic habitat. Abrupt and spectacular changes in skeletal structures occurring when a fish takes on its juvenile form were highlighted in flatfish, bonefish, tarpon, eels, pearlfish and lampreys. However, few studies are devoted to the changes in skeleton during the settlement period of demersal coral reef fishes. In the present study conducted at Rangiroa Atoll (French Polynesia), we highlight an unexpected scales development in A. trisostegus during a fifteen days period just after the reef settlement. Fish was collected during the settlement and reared in aquaria. The osseous skeleton was displayed by a standard Alizarin red S staining technique. At settlement (t0) (SL = 22-25 mm), A. triostegus showed calcified and very long plates, lying in the dermis on the whole body. After three days, some small scales developed on the caudal peduncle. The plates seemed unchanged from the head to the pectoral girdle but were thinner on the trunk. The thin plates are pricked with whitish spots, which seem to indicate a poorer fixation of the alizarin corresponding to a decalcification process. Six days after the settlement, the squamation extended anteriorly to the pectoral girdle by the addition of new scales. Thin plates were always present on the head. Then the density of scales rapidly increased along the trunk during the following three days. The scales appeared on the head nine days after the settlement. Clearly, the plates do not transform into scales. The plates disappearance and the scales appearance appear as two parallel phenomena in the development. [less ▲]

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See detailBipartite life cycle of coral reef fishes promotes increasing shape disparity of the head skeleton during ontogeny.
Frederich, Bruno ULg; Vandewalle, Pierre ULg

Conference (2009, April)

Disparity is a major theme in the paleobiological literature. Most studies of disparity have focused on its temporal dynamics over a geological time scale and generally show that phenotypic disparity ... [more ▼]

Disparity is a major theme in the paleobiological literature. Most studies of disparity have focused on its temporal dynamics over a geological time scale and generally show that phenotypic disparity decreases or remains stable in numerous groups. Surprisingly, the relationship between ontogeny and disparity has received little attention. The ontogenetic dynamics of shape disparity are influenced by diverse interactions such as developmental constraints and/or environmental factors. Coral reefs have an extraordinary diversity of fishes. As the majority of demersal coral reef fishes, the damselfishes (Pomacentridae) have a bipartite life cycle. During the pelagic dispersion phase, all larvae feed on planktonic preys. On the other hand, juveniles and adults associated to the coral reef environment show a high diversity of diets. We test the hypothesis that this ontogenetic change in habitat and diet is related to an increase of shape disparity in head skeletal units (neurocranium, suspensorium, opercle, mandible and premaxilla). We also compare ontogenies of shape among eight species of damselfishes to identify the evolutionary changes in developmental processes modifying shape disparity. By comparing levels of disparity between the eight species at three developmental stages, at the end of the larval phase (reef settlement), at 60 mm SL, and at maximum adult body size, we found that disparity increases significantly during ontogeny. At the end of the larval stage, all skeletal units are already species-specific. The ontogenies of shape are highly divergent among species. At least, evolutionary changes affected three parameters of ontogenetic trajectories of shape in this group: (1) the allometric pattern (the direction in which the vector representing the ontogeny of shape point), (2) the amount of change undergone during the juvenile and adult phases and (3) the rate of shape changes. The interactions among environmental constraints and the three developmental parameters are responsible for increasing disparity. [less ▲]

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See detailTrophic niches of thirteen damselfishes (Pomacentridae) at the Grand Récif of Toliara, Madagascar
Frederich, Bruno ULg; Fabri, Grégory ULg; Lepoint, Gilles ULg et al

in Ichthyological Research (2009), 56

The damselfishes, with more than 340 species, constitute one of the most important families that live in the coral reef environment. Most of our knowledge of reef-fish ecology is based on this family, but ... [more ▼]

The damselfishes, with more than 340 species, constitute one of the most important families that live in the coral reef environment. Most of our knowledge of reef-fish ecology is based on this family, but their trophic ecology is poorly understood. The aim of the present study was to determine the trophic niches of 13 sympatric species of damselfishes by combining stable isotope (d15N and d13C) and stomach content analyses. Isotopic signatures reveal three main groups according to their foraging strategies: pelagic feeders (Abudefduf sexfasciatus, A. sparoides, A. vaigiensis, Chromis ternatensis, C. dimidiata, Dascyllus trimaculatus and Pomacentrus caeruleus), benthic feeders (Chrysiptera unimaculata, Plectroglyphidodon lacrymatus and Amphiprion akallopisos) and an intermediate group (D. aruanus, P. baenschi and P. trilineatus). Stomach contents reveal that planktonic copepods and filamentous algae mainly represent the diets of pelagic feeders and benthic feeders, respectively. The intermediate position of the third group resulted from a partitioning of small planktonic prey, small vagile invertebrates and filamentous algae. In this last feeding group, the presence of a wide range of d13C values in P. trilineatus suggests a larger trophic niche width, related to diet-switching over time. Some general considerations about the feeding habits of damselfishes reveal that their choice of habitat on the reef and their behavior appear to be good predictors of diet in this group. Benthic (algae and/or small invertebrates) feeders appear to be solitary and defend a small territory on the bottom; zooplankton feeders remain in groups just above the reef, in the water column. [less ▲]

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See detailSound production in four damselfish (Dascyllus) species: phyletic relationships?
Parmentier, Eric ULg; Lecchini, David; Frederich, Bruno ULg et al

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 ▲]

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See detailOntogenetic determinism of colour polymorphism in a coral reef fish, Chrysiptera brownriggii (Pomacentridae)
Frederich, Bruno ULg; Brié, Christophe; Santos, Raphael et al

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 ▲]

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See detail15th Benelux Congress of Zoology abstract book
Colleye, Orphal ULg; Dauby, Patrick ULg; Fabri, Gregory et al

Book published by Editions de l'université de Liège (2008)

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