MALE AND FEMALE MITOCHONDRIAL-DNA LINEAGES IN THE BLUE MUSSEL (MYTILUS-EDULIS) SPECIES GROUP

In blue mussels of the Mytilus edulis species complex, mitochondrial D NA (mtDNA) inheritance is coupled with gender. Females receive their m other's mtDNA and pass it on to both their daughters and sons. In addi tion, males receive mtDNA from their father and transmit this male mtD NA to their sons. If this pattern of ''doubly uniparental inheritance' ' is older than the M. edulis species complex, then all members of thi s group must have two distinct mtDNA lineages: a maternal lineage that is transmitted through females and a paternal lineage that is transmi tted through males. To test this hypothesis, we scored mtDNA variation in two taxa in this complex, M. edulis and M. trossulus, by means of restriction fragment profiles of whole-mtDNA genomes and DNA sequence of a region of the cytochrome c oxidase subunit III gene (COIII). The various mitotypes present in these mussels were classified as ''male'' or ''female'' based on their gender association and as belonging to M . edulis or M. trossulus based on species-specific allozymes. Both max imum parsimony and neighbor-joining phylogenies based on the COIII seq uences grouped female and male mtDNAs into two distinct lineages irres pective of specific origin in accordance with the hypothesis that the origin of these lineages predates the divergence of M. edulis and M. t rossulus.