Mitochondrial DNA variation and genetic structure in populations of Drosophila melanogaster

The understanding of the genetic structure of a species can be improved byconsidering together data from different types of genetic markers. In thepast, a number of worldwide populations of Drosophila melanogaster havebeen extensively studied for several such markers, including allozymes,chromosomal inversions, and quantitative characters. Here we presentresults from a study of restriction- fragment-length polymorphisms ofmitochondrial DNA (mtDNA) in 92 isofemale lines from many of the samegeographic populations of D. melanogaster. Eleven restriction enzymes wereused, of which four revealed restriction-site polymorphism. A total of 24different haplotypes were observed, of which 18 were unique to singlepopulations. In many populations, the unique haplotypes have reached highfrequency without being observed in neighboring populations. A Wagnerparsimony tree reveals that mutationally close variants show geographicalclumping, suggesting local differentiation of mtDNA in populations. TheOld-World and the New-World populations are differentiated, with thepredominant Old-World haplotype being virtually absent from the New World.These results contrast with those for the nuclear genes, in which many locishow parallel clines in different continents, and suggest a common originof D. melanogaster populations in North America.