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2018-12-15 - Colloque/Présentation - communication orale - Anglais - page(s)

Lourtie Alexia , Duchatelet Laurent, Delroisse Jérôme , Straube Nicolas, Mallefet Jérôme, "Evolution of placoid scales in deep-water sharks: from morphology to atomic composition" in The 25th Benelux congress of Zoology, “Zoology in the Anthropocene”, Anvers, Belgique, 2018

  • Codes CREF : Océanographie biologique (DI3191), Evolution des espèces (DI3127), Sciences exactes et naturelles (DI1000), Ecologie (DI3123), Morphologie des espèces [zoologie] (DI3129)
  • Unités de recherche UMONS : Biologie des Organismes Marins et Biomimétisme (S864)
Texte intégral :

Abstract(s) :

(Anglais) Deep-sea environment represents a wide proportion of the world surface. However, it still remains largely mysterious and poorly studied. Deep-sea ecosystems show a lush and extremely diversified fauna, which sometimes presents surprising characteristics such as bioluminescence! Up to now, scientists consider that only 1% of the entire biotope was sampled. Within this environment, elasmobranches are mainly represented by Etmopteridae, Centrophoridae, Squalidae, or Somniosidae families belonging essentially to the Squaliformes. The present study focused on placoid scales (i.e., scales structurally homologous with vertebrate teeth) of 33 shark species from this order. These scales are associated with the skin and involved in different ecological functions such as the reduction of the drag, the defence against parasitism/predators or abrasion but it is also suggested that they might be functionally related to bioluminescence transmission in luminous species. Based on 33 deep-water shark species, this study makes a comparison of the morphological features and composition of ventral skin placoid scales. Thanks to Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectrometry (EDX) analyses, morphometric and atomic composition measurements have been performed. Multivariate statistical analyses (ACP) were performed to determine clade-specific features. According to the known phylogeny of Squaliformes, character-mapping approach was used to predict ancestral character states and assess their conservation along the lineage. Our results clearly highlight a conserved and stereotypical composition of the scales among Squaliformes but, conversely, also demonstrate striking morphological differences between families. Character-mapping reconstruction allow to assess the evolution of various traits within Squaliformes (e.g., shield-like placoid scale morphotype is ancestral), and particularly the link between morphological features and bioluminescence for specific families (e.g., surface occupied by scales reduced in luminous clades). All these results, deriving from an unprecedented sampling, shed light on morphological diversity and composition variation of placoid scales in deep-sea elasmobranches and, more generally, on the adaptations of deep-sea sharks to their mysterious environment.


Mots-clés :
  • (Anglais) Morpho-mapping
  • (Anglais) Elasmobranchs
  • (Anglais) Shark denticle
  • (Anglais) Bioluminescence
  • (Anglais) Evolution