THE EFFECTS OF NATURAL HYBRIDIZATION ON THE REGULATION OF DOUBLY UNIPARENTAL MTDNA INHERITANCE IN BLUE MUSSELS (MYTILUS SPP)

Blue mussels in the Mytilus edulis species complex have a doubly unipa rental mode of mtDNA inheritance with separate maternal and paternal m tDNA lineages. Female mussels inherit their mtDNA solely from their mo ther, while males inherit mtDNA from both parents. In the male gonad t he paternal mtDNA is preferentially replicated so that only paternal m tDNA is transmitted from fathers to sons. Hybridization is common amon g differentiated blue mussel taxa; whenever it involves M. trossulus, doubly uniparental mtDNA inheritance is disrupted. We have found high frequencies of males without and females with paternal mtDNA among hyb rid mussels produced by interspecific matings between M. galloprovinci alis and M. trossulus. In contrast, hybridization between M. galloprov incialis and M. edulis does not affect doubly uniparental inheritance, indicating a difference in the divergence of the mechanisms regulatin g mtDNA inheritance among the three blue mussel taxa. Our data indicat e a high frequency of disrupted mtDNA transmission in F-1 hybrids and suggest that two separate mechanisms, one regulating the transmission of paternal mtDNA to males and another inhibiting the establishment of paternal mtDNA in females, act to regulate doubly uniparental inherit ance. We propose a model for the regulation of doubly uniparental inhe ritance that is consistent with these observations.