Population genetics of two allopatric (North Sea and Baltic Sea) populations of Evadne nordmanni (Podonidae): Similarities and differences

This study assessed the genetic relationship between Evadne nordmanni of the Baltic Sea and the North Sea from sequence variation of the mitochondrial cytochrome c oxidase subunit I gene (COI) of 88 specimens from 13 different sites, and from further published data from the Atlantic and Pacific basins. The COI sequences of E. nordmanni from the North and Baltic Seas were represented by a coherent cluster of 28 haplotypes dominated by a central haplotype that accounted for over half of the individuals from these seas, from all samples except one from the Arkona Basin (Baltic Sea). Overall, the North and Baltic Sea populations appear relatively homogenous and the North Sea plausibly represents the source population for the Baltic one. However, the haplotype network also involved a haplogroup of exclusively Baltic Sea haplotypes, comprising four haplotypes represented by 21 individuals and strongly dominated by specimens from the Arkona basin. This inspires discussion about the post-glacial evolution of a genetically distinct Baltic Sea group, related to a special local salinity regime. Partly as a reflection of the presence of the unique haplogroup, the mean haplotype diversity in the Baltic was twice as high as the mean diversity in the North Sea, h = 0.64 versus h = 0.30.