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The "Crustacean Seas" — an evolutionary perspective on the Ponto–Caspian peracarids

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Abstract:

A spectacular adaptive radiation of crustaceans has occurred in the Black, Caspian, and Aral seas. This study tests several evolutionary scenarios based on the extent of genetic differentiation and the phylogenetic relationships among endemic mysids and gammarid amphipods from the Black and Caspian seas. Molecular phylogenies for these taxa were based on two mitochondrial genes: cytochrome c oxidase subunit I and the large ribosomal RNA subunit (16S), and one nuclear gene, the large ribosomal RNA subunit (28S). The results support the monophyly of the Ponto–Caspian gammarids (genera Dikerogammarus, Echinogammarus, Obesogammarus, and Pontogammarus), suggesting their origin from one colonization event. By contrast, several colonization events preceded the radiation of the Ponto–Caspian mysids (genera Limnomysis and Paramysis). Levels of intraspecific divergence were variable, with mysids showing either no geographic structure or deep genetic splits reflecting a long history of reproductive isolation between populations in marine settings and those in fresh waters. These findings suggest that the diversity of the Ponto–Caspian crustaceans has been underestimated and that species regarded as euryhaline are often composed of distinct evolutionary groups whose taxonomic status should be reevaluated.

Il s'est produit une extraordinaire radiation des crustacés dans la mer Noire, la mer Caspienne et la mer d'Aral. Nous évaluons plusieurs scénarios évolutifs basés sur l'étendue de la différentiation génétique et les relations phylogénétiques chez les mysidés et les amphipodes gammaridés endémiques des mers Noire et Caspienne. Les phylogénies moléculaires de ces taxons se basent sur deux gènes mitochondriaux, la sous-unité I de la cytochrome c oxydase et la grande sous-unité d'ARN ribosomique (16S), ainsi qu'un gène nucléaire, la grande sous-unité d'ARN ribosomique (28S). Nos résultats appuient l'hypothèse de la monophylie des gammaridés Ponto–Caspiens (genres Dikerogammarus, Echinogammarus, Obesogammarus et Pontogammarus), ce qui laisse croire qu'ils sont issus d'un même épisode de colonisation. En revanche, plusieurs épisodes de colonisation ont précédé la radiation des mysidés Ponto–Caspiens (genres Limnomysis et Paramysis). Les niveaux de divergence interspécifique sont variables : chez les mysidés, ou bien il n'y a pas de structure géographique, ou alors il y a d'importantes divergences génétiques qui reflètent une longue période d'isolement génétique entre les populations des milieux marins et celles d'eau douce. Ces résultats indiquent que la diversité des crustacés ponto-caspiens a été sous-estimée et que les espèces considérées comme euryhalines sont souvent composées de groupes évolutifs distincts dont le statut taxonomique a besoin d'être réévalué.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: March 1, 2005

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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