Genetic divergence, range expansion and possible homoploid hybrid speciation among pine species in northeast China

Although homoploid hybrid speciation in plants is probably more common than previously realized, there are few well-documented cases of homoploid hybrid origin in conifers. We examined genetic divergence between two currently widespread pines in northeast China, Pinus sylvestris var. mongolica and P. densiflora, and also whether two narrowly distributed pines in the same region, P. funebris and P. takahasii, might have originated from the two widespread species by homoploid hybrid speciation. Our results, based on population genetic analysis of chloroplast (cp), mitochondrial (mt) DNA, and nuclear gene sequence variation, showed that the two widespread species were divergent for both cp- and mtDNA variation, and also for haplotype variation at two of eight nuclear gene loci surveyed. Our analysis further indicated that P. sylvestris var. mongolica and P. densiflora remained allopatric during the most severe Quaternary glacial period that occurred in northeast China, but subsequently exh...