Two seas, two lineages: How genetic diversity is structured in Atlantic and Mediterranean greater amberjack Seriola dumerili Risso, 1810 (Perciformes, Carangidae)

- We analysed contemporary and historical population events of Seriola dumerili and rivoliana by nuclear and mtDNA genes.
- The results suggest absence of populations genetic structure within the Mediterranean Sea.
- Mitochondrial dichotomy was recorded within S. dumerili.
- Reduced gene flow between Atlantic and Mediterranean populations at all loci examined was noted.
- These populations can be seen as individual genetic stocks and it is important to manage them separately.

The vastness of the ocean and our limited ability to observe and monitor the organisms therein make molecular markers particularly useful tools in the investigation of the ecology and evolutionary biology of fish. Nowadays, due to increased demand of fish foods, genetic researches are focused on new candidate species for aquaculture, such as Seriola species. Here, the analyses of eight polymorphic nuclear microsatellites loci and three mitochondrial (mt) DNA genes (16S-rRNA, Cyt-b, and D-Loop) in the greater amberjack, Seriola dumerili, detected breakpoint between Atlantic and Mediterranean populations, presumably arisen by the oceanographic features of the Almeria-Oran Front opposed to the gene flow of the species. Still, an absence of heterogeneity between the sampling locations within the Mediterranean Sea was noted, although an observed dichotomous structure of the phylogenetic mtDNA tree revealed two clades, with no spatial division within the basin. The origin of these two clades likely predates the late Pleistocene or Holocene colonization of the species from the Atlantic Ocean into the Mediterranean Sea. In addition, some preliminary genetic information are provided for Seriola rivoliana, the species that has been recently recognized as an Atlantic migrant in the Mediterranean.