Restriction-Site Heteroplasmy in Anchovy (Engradis encrasicolus) Indicates Incidental Biparental Inheritance of Mitochondrial DNA1

Presence in the same individual of two highly diverged types of mitochondrial DNA (mtDNA) implies either that the two types accumulated mutational differences while coexisting in the same female lineage or that two independently diverged lineages anastomosed through biparental transmission. Cleavage-site mtDNA analysis in anchovies revealed 3 heteroplasmic individuals among 435 examined. All three contained the same two types of molecules that differed at 7 cleavage sites in a total of 26 surveyed by seven restriction endonucleases. Estimates of the time of heteroplasmy persistence in other species are much shorter than the time needed for this level of divergence. No heteroplasmic individuals were found for mtDNA molecules differing by fewer cleavage sites. This also argues against the hypothesis of gradual divergence in a single lineage, as it would imply selective removal of much more frequently occurring lower-level heteroplasmies. The two types of molecules found in heteroplasmy were the most common in the population, as expected from the hypothesis of paternal leakage. We conclude that the heteroplasmy that we have observed resulted from biparental mtDNA inheritance in anchovies.