Footprints of unconventional mitochondrial inheritance in bivalve phylogeny: Signatures of positive selection on clades with doubly uniparental inheritance.

The doubly uniparental inheritance (DUI) of some bivalve mollusks is the major exception to the common maternal inheritance of mitochondria in animals. DUI involves two mitochondrial lineages with paternal and maternal transmission routes, and it appears as a complex phenomenon requiring both nuclear and mitochondrial adaptations. DUI distribution seems to be scattered among the Bivalvia, and there are several clues for its multiple origins. In this paper, we investigate whether the incipient DUI systems had left possible selective signatures on mitochondrial gen- omes. Alongside the outstanding divergence of amino acid sequences, we confirmed strong purifying selection to act on mitochondrial genes. However, we found evi- dence that distinct episodes of intense directional pressure are associated with the origins of different DUI systems: We interpret these signals as footprints of the coevolution with the nuclear genome that ought to take place at the base of a DUI clade. Six genes (atp6, cox1, cox2, cox3, nad4L, and nad6) seem to be more com- monly linked to the appearance of DUI. We also identified few putative DUI‐specific mutations, thus extending support to the hypothesis of multiple independent origins of this complex phenomenon.