DNA Barcoding Case Studies

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Scope

The Western Mediterranean provides a unique opportunity to study factors regulating species diversity. In fact, this sea is a “hot-spot” of marine biodiversity and endemism is also very high (ca. 25% of the whole Mediterranean biota). About 8000 marine species including ca. 1500 macroalgae are widespread along both the continental (Europe and Africa) and insular coasts (e.g Balearic islands, Corsica, Sardinia). This geographical configuration provides continuous and isolated habitats to evaluate the influence of factors such as reproductive isolation and long distance dispersal on genetic divergence in marine algae. Furthermore, marine biodiversity of the Mediterranean is considered to reside, at least partly, on the tormented geological history of this basin, which consisted of successive isolations and exchanges with the Atlantic and the Indian oceans. Despite ongoing debates on the mechanisms of geological formation for the Mediterranean, the time line of events is relatively well known and provides us with geological dates to infer the dynamics of long-term speciation. In addition, the excavation of the Suez Canal in 1869 artificially reconnected the Red Sea to the eastern Mediterranean leading to occasional introduction of species from the Indo Pacific and providing us with a model for dispersal and more recent speciation.

Purpose

The aim of this project is to study brown and red algal diversity (ca. 1100 taxa) in the Western Mediterranean to assess species limits among these taxa. Toward this goal, an extensive sampling of brown and red algae (ca. 20,000 samples) will be performed all around the western mediterranean basin. Reliable species assignment will be conducted on every sample using the DNA-barcode (5’end of the mitochondrial gene cox1) in addition to morphological and anatomical observations.

Background

Publications on systematics of algae from the Mediterranean are plentiful but generally they have been limited to regional studies or to monographies on a few taxa. To date, the only flora available for this part of the world is the first volume of the Iberian phycological flora devoted to the single order Fucales (Pheophyceae) ; there is therefore a lack of keys for reliable identification of most red and brown algae from the Mediterranean. Furthermore, marine macroalgae are notoriously difficult to identify owing to their relatively simple morphology and anatomy. Traditionally, taxonomic identification methods have emphasized vegetative and reproductive features that are subject to high variability and are often ineffective for discriminating species. For example: i) marine macroalgae occur in relatively challenging conditions which can lead to high levels of morphological convergence as a response to environmental constraints; ii) their life cycles are incompletely understood and can exhibit alternation of heteromorphic generations; iii) they are subject to phenotypic variations in response to environmental factors (which may be a concern for panoceanic species because the Mediterranean Sea presents some distinctive abiotic features (e.g. small tidal range, high salinity, highly stratified waters in summertime); and last but not least, iv)speciation is not always accompanied by (obvious) morphological changes. As such, there are potentially many inconsistencies in taxonomic identification in the Mediterranean flora.

Logistics

Sampling will be performed extensively in ecological, geographical and temporal scales to provide data on distribution and phenology of species Each sample will be pressed on herbarium paper and kept as a voucher specimen. Subsamples of each specimen will be dried in silica gel and subsequently used for DNA analysis. Collection information including description of the habitat will be consigned in the MNHN database. Vouchers will be stored in the PC herbarium, MNHN, Paris. Molecular identification of each collected sample will be performed using the ‘DNA-barcode’ (the 5’ end of the mitochondrial gene cox1 (cytochrome oxidase subunit I)). Molecular data will be logged in BOLD (barcode of life data base) and cluster analyses of the DNA-barcode will be performed to assess species assignments. Each molecular entity will be subject to further taxonomic investigation. If possible, we will characterize vegetative and reproductive features that are significant for reliable species identification. Taxonomic information of characterized species will be uploaded to BOLD.

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