SEX-LIMITED MITOCHONDRIAL-DNA TRANSMISSION IN THE MARINE MUSSEL MYTILUS-EDULIS

Mitochondrial DNA (mtDNA) was thought to be inherited maternally in an imals, although paternal leakage has been reported in mice and Drosoph ila, Recently, direct evidence of extensive paternal inheritance of mt DNA has been found in the marine mussel Mytilus. We give evidence that whereas female mussels are homoplasmic for a genome that is transmitt ed to eggs, male mussels are heteroplasmic for this genome and for a s econd genome that is transmitted preferentially to sperm. The results provide support for the existence of separate male and female routes o f mtDNA inheritance in mussels. The two genomes Show a base sequence d ivergence exceeding 20% at three protein coding genes, consistent with long term maintenance of the heteroplasmic state. We propose that the two genomes differ in fitness in males and females, possibly as a res ult of interaction with nuclear genes.