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Aquatic Biology

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AB 21:25-36 (2014)  -  DOI:

New SNP markers reveal largely concordant clinal variation across the hybrid zone between Mytilus spp. in the Baltic Sea

Małgorzata Zbawicka1,*, Tomasz Sańko1, Jakob Strand2, Roman Wenne1

1Institute of Oceanology PAS, Powstańców Warszawy 55, 81-712 Sopot, Poland
2Arhus University, Department of Bioscience, 4000 Roskilde, Denmark
*Corresponding author:

ABSTRACT: Environmental conditions such as a pronounced salinity gradient and postglacial history make the Baltic Sea a suitable area for studying how selection and gene flow affect genetic differentiation in marine species. A cDNA library was used to identify new single nucleotide polymorphisms (SNPs) in Baltic populations of Mytilus spp. mussels. Sixty polymorphic SNPs were used to genotype 642 individual mussels from the inner Baltic, Danish Straits, northwest Denmark and a population of the northeast Pacific. We characterized 49 novel SNP markers that differentiate the populations of the North and Baltic Sea areas. Concordant narrow clines were observed at the entrance of the Baltic Sea for most of these markers. Considerable variance of hybrid index scores was observed in populations with intermediate allele frequencies within the hybrid zone, e.g. in Gedser and Hjelm. The presented results are in accordance with the existence of strong reproductive isolation, probably caused by a combination of exogenous (e.g. adaptation to brackish waters) and endogenous pre- and post-zygotic factors (e.g. selection against hybrids). The overwhelming majority of new SNPs markers showed a larger representation of M. trossulus than M. edulis genes in the nuclear DNA of Baltic Mytilus species. Finally, we identified a few markers with an elevated level of introgression of M. edulis alleles in the Baltic Sea M. trossulus populations in comparison to the reference M. trossulus population of the Pacific.

KEY WORDS: Population structure · Hybrid index score · Single locus clines · Diagnostic markers

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Cite this article as: Zbawicka M, Sańko T, Strand J, Wenne R (2014) New SNP markers reveal largely concordant clinal variation across the hybrid zone between Mytilus spp. in the Baltic Sea. Aquat Biol 21:25-36.

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