Genome‐wide insights into introgression and its consequences for genome‐wide heterozygosity in the Mytilus species complex across Europe
2020
The three mussel species comprising the Mytilus complex are widespread across
Europe and readily hybridize when they occur in sympatry, resulting in a mosaic of
populations with varying genomic backgrounds. Two of these species, M. edulis and
M. galloprovincialis, are extensively cultivated across Europe, with annual produc-
tion exceeding 230,000 tonnes. The third species, M. trossulus, is considered com-
mercially damaging as hybridization with this species results in weaker shells and
poor meat quality. We therefore used restriction site associated DNA sequencing
to generate high-resolution insights into the structure of the Mytilus complex across
Europe and to resolve patterns of introgression. Inferred species distributions were
concordant with the results of previous studies based on smaller numbers of ge-
netic markers, with M. edulis and M. galloprovincialis predominating in northern and
southern Europe respectively, while introgression between these species was most
pronounced in northern France and the Shetland Islands. We also detected traces
of M. trossulus ancestry in several northern European populations, especially around
the Baltic and in northern Scotland. Finally, genome-wide heterozygosity, whether
quantified at the population or individual level, was lowest in M. edulis, intermediate
in M. galloprovincialis, and highest in M. trossulus, while introgression was positively
associated with heterozygosity in M. edulis but negatively associated with heterozy-
gosity in M. galloprovincialis. Our study will help to inform mussel aquaculture by
providing baseline information on the genomic backgrounds of different Mytilus pop-
ulations across Europe and by elucidating the effects of introgression on genome-
wide heterozygosity, which is known to influence commercially important traits such
as growth, viability, and fecundity in mussels
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