BackgroundBiologists have long been fascinated by the striking diversity of complex color patterns in tropical reef fishes. However, the origins and evolution of this diversity are still poorly understood. Disentangling the evolution of simple color patterns offers the opportunity to dissect both ultimate and proximate causes underlying color diversity.ResultsHere, we study clownfishes, a tribe of 30 species within the Pomacentridae that displays a relatively simple color pattern made of zero to three vertical white stripes on a dark body background. Mapping the number of white stripes on the evolutionary tree of clownfishes reveals that their color pattern diversification results from successive caudal to rostral losses of stripes. Moreover, we demonstrate that stripes always appear with a rostral to caudal stereotyped sequence during larval to juvenile transition. Drug treatments (TAE 684) during this period leads to a dose-dependent loss of stripes, demonstrating that white stripes are made of iridophores and that these cells initiate the stripe formation. Surprisingly, juveniles of several species (e.g., Amphiprion frenatus) have supplementary stripes when compared to their respective adults. These stripes disappear caudo-rostrally during the juvenile phase leading to the definitive color pattern. Remarkably, the reduction of stripe number over ontogeny matches the sequences of stripe losses during evolution, showing that color pattern diversification among clownfish lineages results from changes in developmental processes. Finally, we reveal that the diversity of striped patterns plays a key role for species recognition.ConclusionsOverall, our findings illustrate how developmental, ecological, and social processes have shaped the diversification of color patterns during the radiation of an emblematic coral reef fish lineage.Electronic supplementary materialThe online version of this article (10.1186/s12915-018-0559-7) contains supplementary material, which is available to authorized users.
Background The clownfish Amphiprion ocellaris is one of the rare coral reef fish species that can be reared in aquaria. With relatively short embryonic and larval development, it could be used as a model species to study the impact of global changes such as temperature rise or anthropogenic threats (eg, pollution) on the postembryonic development at molecular and endocrinological levels. Establishing a developmental table allows us to standardize sampling for the scientific community willing to conduct experiments on this species on different areas: ecology, evolution, and developmental biology. Results Here, we describe the postembryonic developmental stages for the clownfish A. ocellaris from hatching to juvenile stages (30 days posthatching). We quantitatively followed the postembryonic growth and described qualitative traits: head, paired and unpaired fins, notochord flexion, and pigmentation changes. The occurrence of these changes over time allowed us to define seven stages, for which we provide precise descriptions. Conclusions Our work gives an easy system to determine A. ocellaris postembryonic stages allowing, thus, to develop this species as a model species for coral reef fishes. In light of global warming, the access to the full postembryonic development stages of coral reef fish is important to determine stressors that can affect such processes.
The present study described the neuro-anatomy of a larval coral reef fish Amphiprion ocellaris and hypothesized that morphological changes during the transition from the oceanic environment to a reef environment (i.e. recruitment) have the potential to be driven by changes to environmental conditions and associated changes to cognitive requirements. Quantitative comparisons were made of the relative development of three specific brain areas (telencephalon, mesencephalon and cerebellum) between 6 days post-hatch (dph) larvae (oceanic phase) and 11 dph (at reef recruitment). The results showed that 6 dph larvae had at least two larger structures (telencephalon and mesencephalon) than 11 dph larvae, while the size of cerebellum remained identical. These results suggest that the structure and organization of the brain may reflect the cognitive demands at every stage of development. This study initiates analysis of the relationship between behavioural ecology and neuroscience in coral reef fishes.
Résumé :L'élaboration des Eurocodes, normes européennes sur le calcul des constructions, a été menée depuis les années 80. Ils sont basés sur les méthodes semi-probabilistes qui introduisent des coefficients partiels. Actuellement, peu de logiciels sont capables de prendre en compte cette approche semi-probabiliste. Mots-clés :Ducs d'Albe -Analyse élasto-plastique -approche semi-probabiliste -EurocodesLogiciel.
Ingénieur chargé d'études, CETMEF Compiègne Résumé: Les premiers retours d'expérience de ROSA 2000 montrent que la mauvaise adaptation des outils de calculs actuels au format de calcul semi-probabiliste complique la vérification aux états-limites des ouvrages. Une étude de recensement et d'évaluation des outils de calcul existant au niveau européen a été lancée. 154 logiciels ont pu être recensés. Leur étude a permis de constater que pour un ouvrage donné il existe un grand nombre de méthodes de calcul différentes, chaque pays privilégiant l'utilisation d'une ou plusieurs méthodes de reconnaissance géotechnique et de calcul. La proportion de logiciels adaptés à l'utilisation des coefficients partiels de sécurité reste faible (20%). Afin de faciliter la mise en oeuvre de ROSA 2000 des propositions sont faites pour adapter rapidement les logiciels existants.
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