Structures génétique et démographique des populations de deux espèces d'ophiures aux caractéristiques biologiques contrastées, Acrocnida brachiata et Ophiothrix fragilis, en Atlantique Nord-Est

Abstract : Nowadays species distribution mainly depends on population history and abilities of migrants to colonize new territories. Dispersal capacities of marine organisms are mainly related to the time spent in the water column by larvae and by habitat fragmentation. Two species of brittle-star of the North-East Atlantic, A. brachiata and O.fragilis, which show different life history traits, have been studied. Parallel population genetics and dynamics approaches have been chosen in the aim of better delineate how past and present gene flow may explain the actual distribution of species. A. brachiata includes two ecotypic sibling species which diverge 5 My ago, at the Mio-Pliocene transition. One lineage lives in intertidal, the second in subtidal. Colonization history seems to differ between these two lineages, because of different glacial refugia localisation. Populations are highly genetically structured: flow is mainly reduced due to a short larval phase and the high level of habitat fragmentation. Hybridization between lineages occur at low rate due to selection against hybrids in both habitat during recruitment. Adult migration might occur and is likely to homogenise genetic structure at microspatial scale. Demographic functioning seems to show a pluri-annual cycle as annual recruitment seems insufficient to ensure population sustainability. O. fragilis is also a complex of two sibling species, one in the Southern Europe, the other one on North- Atlantic coasts. The latter is divided into two ecotypic varieties, one mainly adapted to subtidal life, the other to the intertidal one. Co-occurrence of the two varieties induces a first level of genetic structure. Actually, most of the genetic structure is due to local processes and not to geographical isolation, in agreement with a species displaying a long larval phase and living in continuous habitat. These local processes seem to induce a temporal Walhund effect, probably due to a metapopulation functioning. Great disparities in population dynamics between sites may also contribute to the chaotic genetic structure of populations. Results obtained for these two species provide new insights on how past history influence species distribution and how local processes play a major role in structuring populations.
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  • HAL Id : tel-01117696, version 1

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Delphine Muths. Structures génétique et démographique des populations de deux espèces d'ophiures aux caractéristiques biologiques contrastées, Acrocnida brachiata et Ophiothrix fragilis, en Atlantique Nord-Est. Génomique, Transcriptomique et Protéomique [q-bio.GN]. Paris 6, 2006. Français. ⟨tel-01117696⟩

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