Patterns of genetic differentiation between two co-occurring demersal species; the red mullet (Mullus barbatus) and the striped red mullet (Mullus surmuletus).

Abstract

[EN]The accurate identification of genetic partitioning is of primarily importance when devising conservation management strategies for today’s marine resources. The great variety of genetic structure displayed by demersal species underscores the need for the identification of common patterns that can be found across species. Here, we analyse allele frequency variation at 10 microsatellite loci of two congener demersal fish, the red mullet (Mullus barbatus) and the striped red mullet (Mullus surmuletus), from the Atlantic Ocean and the Mediterranean Sea. The results indicate that two different gene flow patterns exist between these species. The red mullet’s genetic distribution was found to be highly structured, resembling that of a metapopulation composed by independent, self-recruiting subpopulations with some connections between them. The striped red mullet displayed less genetic heterogeneity within the Mediterranean Sea and a substantial gene flow reduction between the Atlantic Ocean and Mediterranean Sea. Our results indicate that gene flow patterns in the demersal environment can be substantially different between closely related species with highly comparable biology, suggesting that biogeographic boundaries can affect demersal species in a different way despite common ecological features and spatial overlap. We conclude that the delimitation of such boundaries could be determined by the fine differences in life history traits between species.

[FR]L'identificalion precise du pal1ionnement genetique eSI d'importunce considerable lorsqu'on met au point des strategies de conservation-gestion des ressources marines actuelles. La grande varictc de structures genetiques retrouvees chez les cspeces ctemersales souligne Ie besoin d'identification de patrons communs qui peuvent s'appliquer a I'ensemble des especes. Nous analysons ici la valiation de la frequence des alleles a 10 locus microsatellites chez deux poissons demersaux de meme genre. Ie rouget de vase (Mulllls barbafl/s) et Ie rouget de roche (Mldills sllnll/lletlls) de l'Atlantique et de la Mediterranee. Les resuhats revelent deux patrons de flux genique differents chez ces especes. La distribution genctique du rouget de vase est fortement structuree ressemblant acelie d'une metapopulation composee de sous-populations in· depcndantes arecrutement autonome avec certair:es connections entre elles. Le rouget de roche montre moins d'heterogeneite genetique dans la Mediterranee et une reduction significative du flux genique entre I' Atlantique et la Mediterranee. Nos resultats demontrent que les patrons de nux genique dans Ie milieu demersal peuvent etre tres differents entre des es¢ces fortement apparentees possedant des biologies tres semblables; cela laisse croire que les frontieres biogeographiques peuvent affecter les poissons dCmersaux de faliron differente malgre leurs caracteristiques ecologiques communes et leur chevauchement spatial. Nous concluons que la delimitation de telles fronlieres pourrait se baser sur des differences mineures de traits du cycle biologique entre les especes.