Lineage sorting accounting for the disassociation between chloroplast and mitochondrial lineages in oaks of southern France

Dumolin-Lapegue et al. (Mol. Biol. Evol. 15: 1321-1331. 1998) suggested tha t recurrent inversions of a 4-bp sequence of the mtDNA nad4-1/2 locus due t o intramolecular recombination were responsible for the disassociation of c hloroplast and mitochondrial genomes of French oaks. Based on their PCR-RFL P (PCR - restriction fragment length polymorphism) data obtained from three noncoding spacers, a minimum spanning network representing the phylogeny o f the cpDNA was reconstructed. The mapping of alleles b and c of the mtDNA nad4-1/2 locus on the cpDNA network revealed a nonrandom distribution, whic h contradicted the expected patterns when repeated, and ongoing inversions had been occurring. The fact that polymorphisms (a mixed c + d type) were m ostly restricted to the interior nodes of the network, which represented an cient haplotypes and geographically coincided with probable glacial refugia in southern Europe, agreed with a migrant-pool model. Evidence of a widesp read pattern of polymorphism distribution indicated that mtDNA haplotypes w ere likely to be more ancient than the cpDNA haplotypes. Lineage sorting, d ue to relative age of cpDNA vs. mtDNA, plus the specific migratory mode, wh ich recruited colonists from a random sample of resource populations during glacial expansion (thereby extending the lineage sorting period, LSP), may have resulted in the disassociation of chloroplast and mitochondrial genom es in oaks.