Iterative ecological radiation and convergence during the evolutionary history of damselfishes (Pomacentridae)

in American naturalist (2013), 181(1), 94-113

Coral reef fishes represent one of the most spectacularly diverse assemblages of vertebrates on the planet, but our understand- ing of their mode of diversification remains limited. Here we test whether ... [more ▼]

Coral reef fishes represent one of the most spectacularly diverse assemblages of vertebrates on the planet, but our understand- ing of their mode of diversification remains limited. Here we test whether the diversity of the damselfishes (Pomacentridae), one of the most species-rich families of reef-associated fishes, was produced by a single or multiple adaptive radiation(s) during their evolutionary history. Tests of the tempo of lineage diversification using a time-calibrated phylogeny including 208 species revealed that crown pomacentrid diversification has not slowed through time as expected under a scenario of a single adaptive radiation resulting from an early burst of diversification. Evolutionary modeling of trophic traits similarly rejected the hypothesis of early among-lineage partitioning of ecologically important phenotypic diversity. Instead, damselfishes are shown to have experienced iterative convergent radiations wherein subclades radiate across similar trophic strategies (i.e., pelagic feeders, benthic feeders, intermediate) and morphologies. Regionalization of coral reefs, competition, and functional constraints may have fueled iterative ecological radiation and convergent evolution of damselfishes. Through the Pomacentridae, we illustrate that radiations may be strongly structured by the nature of the constraints on diversification. [less ▲]

Morphological and genetic divergences in a coral reef damselfish, Pomacentrus coelestis

in Evolutionary Biology (2012), 39(3), 359-370

Population differentiation is one of the main topics in evolutionary biology. Except the exploration of color variation, few studies focused on morphological divergences among populations of coral reef ... [more ▼]

Population differentiation is one of the main topics in evolutionary biology. Except the exploration of color variation, few studies focused on morphological divergences among populations of coral reef fishes. In this work, we studied morphological and genetic differentiation among populations of the damselfish, Pomacentrus coelestis, in the northwestern Pacific Ocean. The shapes of the mandible and the premaxilla were explored using geometric morphometric methods and the genetic structure was investigated using microsattelites. Various tests revealed significant shape variation among most P. coelestis populations for both skeletal units. Morphological variation of the mandible accompanies a genetic break between populations of mainland Japan and Okinawa-Taiwan. However, Mantel and Procrustes tests revealed no congruence between morphological and genetic structures. We illustrate that phenotypic plasticity and adaptive divergence are potential evolutionary mechanisms underlying shape difference among P. coelestis populations. An ecomorphological approach suggests that various diet could be related to shape variation of oral jaws. [less ▲]

Effects of alternate reef states on coral reef fish habitat associations

in Environmental Biology of Fishes (2012), 94(2), 421-429

The present study describes ontogenetic shifts in habitat use for 15 species of coral reef fish at Rangiroa Atoll, French Polynesia. The distribution of fish in different habitats at three ontogenetic ... [more ▼]

The present study describes ontogenetic shifts in habitat use for 15 species of coral reef fish at Rangiroa Atoll, French Polynesia. The distribution of fish in different habitats at three ontogenetic stages (new settler, juvenile, and adult) was investigated in coral- dominated and algal-dominated sites at two reefs (fringing reef and inner reef of motu). Three main ontogenetic patterns in habitat use were identified: (1) species that did not change habitats between new settler and juvenile life stages (60% of species) or between juvenile and adult stages (55% of species—no ontoge- netic shift); (2) species that changed habitats at different ontogenetic stages (for the transition “new settler to juvenile stage”: 15% of species; for the transition “juvenile to adult stage”: 20% of species); and (3) species that increased the number of habitats they used over ontogeny (for the transition “new settler to juvenile stage”: 25% of species; for the transition “juvenile to adult stage”: 25% of species). Moreover, the majority of studied species (53%) showed a spatial variability in their ontogenetic pattern of habitat use according to alternate reef states (coral reef vs algal reef), suggesting that reef state can influence the dynamics of habitat associations in coral reef fish. [less ▲]

Etude des mécanismes de prise de nourriture chez le poisson clown Amphiprion clarkii

Poster (2012, March)

Patterns of morphological evolution of the cephalic region in damselfishes (Perciformes: Pomacentridae) of the Eastern Pacific

in Biological Journal of the Linnean Society (2011), 102

Pomacentridae are one of the most abundant fish families inhabiting reefs of tropical and temperate regions. This family, comprising 29 genera, shows a remarkable diversity of habitat preferences, feeding ... [more ▼]

Pomacentridae are one of the most abundant fish families inhabiting reefs of tropical and temperate regions. This family, comprising 29 genera, shows a remarkable diversity of habitat preferences, feeding, and behaviours. Twenty-four species belonging to seven genera have been reported in the Eastern Pacific region. The present study focuses on the relationship between the diet and the cephalic profile in the 24 endemic damselfishes of this region. Feeding habits were determined by means of underwater observations and the gathering of bibliographic data. Variations in cephalic profile were analyzed by means of geometric morphometrics and phylogenetic methods. The present study shows that the 24 species can be grouped into three main trophic guilds: zooplanktivores, algivores, and an intermediate group feeding on small pelagic and benthic preys. Shape variations were low within each genus except for Abudefduf. Phylogenetically adjusted regression reveals that head shape can be explained by differences in feeding habits. The morphometric phylogeny recovered the subfamily Stegastinae and the relationship between Abudefduf troschelii and Chromis species. The cephalic profile of damselfishes contains a clear and strong phylogenetic signal. [less ▲]

Comparison of the adductor mandibulae and jaw lever mechanisms between three damselfishes (Pomacentridae)

Poster (2010, December)

Evolution of ontogenetic allometry shaping giant species: a case study from the damselfish genus Dascyllus (Pomacentridae)

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 ▲]

Evidence of an original scale development during the settlement phase of a coral reef fish (Acanthurus triostegus)

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 ▲]

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

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 ▲]

Evidence of an atypical scale development during the settlement phase of a coral reef fish

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 ▲]