Abstract
Doubly uniparental inheritance (DUI) of mitochondrial DNA is a rare phenomenon occurring in some freshwater and marine bivalves and is usually characterized by the mitochondrial heteroplasmy of male individuals. Previous research on freshwater Unionida mussels showed that hermaphroditic species do not have DUI even if their closest gonochoristic counterparts do. No records showing DUI in a hermaphrodite have ever been reported. Here we show for the first time that the hermaphroditic mussel Semimytilus algosus (Mytilida), very likely has DUI, based on the complete sequences of both mitochondrial DNAs and the distribution of mtDNA types between male and female gonads. The two mitogenomes show considerable divergence (34.7%). The presumably paternal M type mitogenome dominated the male gonads of most studied mussels, while remaining at very low or undetectable levels in the female gonads of the same individuals. If indeed DUI can function in the context of simultaneous hermaphroditism, a change of paradigm regarding its involvement in sex determination is needed. It is apparently associated with gonadal differentiation rather than with sex determination in bivalves.
Highlights
Uniparental inheritance (DUI) of mitochondrial DNA is a rare phenomenon occurring in some freshwater and marine bivalves and is usually characterized by the mitochondrial heteroplasmy of male individuals
As we show in the following article it is the first known hermaphroditic mussel possessing doubly uniparental inheritance, which indicates that Doubly uniparental inheritance (DUI) is connected with gamete differentiation rather than with sex determination in bivalves
Based on the phylogenetic analysis (Fig. 3) the possibility that one of the mitogenomes comes from a contaminating, unrelated organism can safely be discarded: the two mitogenomes, despite the substantial genetic distance, form a sister relationship on the tree
Summary
Uniparental inheritance (DUI) of mitochondrial DNA is a rare phenomenon occurring in some freshwater and marine bivalves and is usually characterized by the mitochondrial heteroplasmy of male individuals. We show for the first time that the hermaphroditic mussel Semimytilus algosus (Mytilida), very likely has DUI, based on the complete sequences of both mitochondrial DNAs and the distribution of mtDNA types between male and female gonads. The presumably paternal M type mitogenome dominated the male gonads of most studied mussels, while remaining at very low or undetectable levels in the female gonads of the same individuals. Hermaphroditic species of freshwater mussels (Unionoida), lose the paternally inherited M mitogenome and the gender-specific open reading frame in the remaining F type mitogenome. As we show in the following article it is the first known hermaphroditic mussel possessing doubly uniparental inheritance, which indicates that DUI is connected with gamete differentiation rather than with sex determination in bivalves
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