Chloroplast and nuclear genetic diversity in northern red oak (Quercus rubra L.)

Northern red oak (Quercus rubra L.) is the dominant native species in the eastern deciduous hardwood forest in the United States. Paleoclimate changes that initiated the retreat of Wisconsinian ice sheet 20,000 years by and subsequent human-mediated disturbance may have profoundly affected genetic diversity and population substructure in Q. rubra . The chloroplast genome persists in local populations, permitting detection of responses to paleoclimate change even after considerable contemporary disturbance. Chloroplast DNA (cpDNA) polymorphisms in 27 populations revealed high genetic differentiation (GST=0.729 +/- 0.107). Two of the five haplotypes detected accounted for 83% of all haplotypes.; To test the hypothesis that a local population will have only one haplotype, I examined chloroplast polymorphisms in 255 northern red oaks in two old growth populations in the Purdue Davis Research Forest (PDRF) and the Pioneer Mothers Memorial Forest (PMMF), the oldest presettlement forest remnant in Indiana. I found four haplotypes and no new haplotypes. In the PMMF, 85% of 34 trees had haplotype III. In the PDRF, 73% of the 134 trees in PD_1 had haplotype V while 68% of the 87 trees in PD_4 had haplotype I. The least frequent haplotype in PD_1 and PD_4 tended to occur at the edge of the fragments. These results showed that most chloroplast polymorphism surveys in forest trees sample too few individuals and that sampling along edges is not a good strategy for detection of the predominant haplotype.; The Q. rubra in the PMMF represent the chloroplast and nuclear genetic diversity existing at that location during presettlement times. I used fifteen nuclear microsatellite and five cpDNA loci to test the hypotheses of zygotic, gametic and cytonuclear equilibrium among these trees. This study revealed extensive zygotic, gametic and cytonuclear disequilibria in this population. Population structure and a parentage analysis revealed evidence for extensive mating among groups of close relatives within the stand. 102 of the 109 trees examined descend from only six related groups of candidate parents. It was hypothesized that highly localized genetic substructure may be the natural condition for this species.