A number of studies have claimed that recombination occurs in animal mtDNA, although this evidence is controversial. Ladoukakis and Zouros (2001) provided strong evidence for mtDNA recombination in the COIII gene in gonadal tissue in the marine mussel Mytilus galloprovincialis from the Black Sea. The recombinant molecules they reported had not however become established in the population from which experimental animals were sampled. In the present study, we provide further evidence of the generality of mtDNA recombination in Mytilus by reporting recombinant mtDNA molecules in a related mussel species, Mytilus trossulus, from the Baltic. The mtDNA region studied begins in the 16S rRNA gene and terminates in the cytochrome b gene and includes a major noncoding region that may be analogous to the D-loop region observed in other animals. Many bivalve species, including some Mytilus species, are unusual in that they have two mtDNA genomes, one of which is inherited maternally (F genome) the other inherited paternally (M genome). Two recombinant variants reported in the present study have population frequencies of 5% and 36% and appear to be mosaic for F-like and M-like sequences. However, both variants have the noncoding region from the M genome, and both are transmitted to sperm like the M genome. We speculate that acquisition of the noncoding region by the recombinant molecules has conferred a paternal role on mtDNA genomes that otherwise resemble the F genome in sequence

Gaining new knowledge of the native distributions of species (phylogeography) is more and more difficult in a world affected by anthropogenic disturbance, in particular by species translocations. Increasingly, molecular markers are required to support decisions about the taxonomy of native vs. introduced species, and the existence of their hybrids, to answer phylogeographic questions. In many fields, including aquaculture, traceability and food security, taxonomic and phylogeographic knowledge is key to the successful management and conservation of biodiversity. The Pacific coast of Chile is one of the last regions without a clear and agreed understanding of the taxonomy and systematics of smooth‐shelled blue mussels of the genus Mytilus. A panel of 49 bi‐allelic single nucleotide polymorphisms (SNPs) was genotyped in 338 Mytilus individuals collected from nine Chilean and five reference populations. All analyses confirmed the hypothesis that the native Chilean blue mussel is genetically distinct from the reference species M. edulis, M. galloprovincialis and M. trossulus. These results support the hypothesis of a unique evolutionary history of the native Chilean blue mussel on the Pacific coast of South America. It is therefore concluded that the native blue mussel from Chile should be recognized as M. chilensis Hupé 1854. We confirmed a recent Mediterranean origin of introduced M. galloprovincialis on the coast of Chile. This knowledge advances the understanding of global phylogeography of blue mussels and their bioinvasions and harmonizes taxonomy in the context of aquaculture production, seafood traceability, labelling and trade.

Semi-sessile Mytilus mussels are used as indicators of climate changes, but their geographic distribution is not sufficiently known in the Arctic. The aim of this study was to investigate the taxonomic status and genetic differentiation of Mytilus populations in a Northwest Greenlandic fjord at Maarmorilik, impacted by contaminations from a former mine. In this study, mussels were collected at three sites differing in exposure to environmental factors. A total of 54 polymorphic SNPs found in the Mytilus EST and DNA sequences analyzed were successfully applied to 256 individuals. The results provided the first evidence for the existence of M. trossulus in Greenland. The mussel from M.trossulus and M. edulis taxa are shown to coexist and hybridize in the fjord. The three studied sites were found to differ significantly in the distribution of taxa with a higher prevalence of M. trossulus in the inner fjord. The identified M. edulis × M. trossulus hybrids mostly had a hybrid index score of about 0.5, indicating a similar number of alleles characteristic for M. trossulus and M. edulis. There was a low number of backcrosses between ‘pure’ taxa and hybrids. This newly discovered hybrid zone between the two taxa is unique in comparison with the Canadian populations. As Mytilus mussels in Greenland hitherto have been regarded as the one taxon M. edulis, the results have importance for biogeography and future monitoring and environmental studies.