Mitochondrial phylogeography of the European sprat (Sprattus sprattus L., Clupeidae) reveals isolated climatically vulnerable populations in the Mediterranean Sea and range expansion in the northeast Atlantic.

We examined the genetic structure of the European sprat (Sprattus sprattus) by means of a 530-bp sequence of the mitochondrial control region from 210 fish originating from seven sampling localities of its distributional range. Phylogeographical analysis of 128 haplotypes showed a phylogenetic separation into two major clades with the Strait of Sicily acting as a barrier to gene flow between them. While no population differentiation was observed based on analysis of molecular variance and net nucleotide differences between samples of the Baltic Sea, the North Sea and the Bay of Biscay nor between the Black Sea and the Bosporus, a strong population differentiation between these samples and two samples from the Mediterranean Sea was found. Further, the biggest genetic distance was observed within the Mediterranean Sea between the populations of the Gulf of Lyon and the Adriatic Sea, indicating genetic isolation of these regions. Low genetic diversities and star-like haplotype networks of both Mediterranean Sea populations point towards recent demographic expansion scenarios after low population size, which is further supported by negative F(S) values and unimodal mismatch distributions with a low mean. Along the northeast Atlantic coast, a northwards range expansion of a large and stable population can be assumed. The history of a diverse but differentiated Black Sea population remains unknown due to uncertainties in the palaeo-oceanography of this sea. Our genetic data did not confirm the presently used classification into subspecies but are only preliminary in the absence of nuclear genetic analyses.