Geographical structure of gene diversity in Quercus petraea (Matt.) Liebl. II: Multilocus patterns of variation

Abstract

INRA, Laboratoire c/a genetique et d'amélioration des arbres forestiers, UP 45, 33611 Gazinet Cedex, France Two-locus composite disequilibria were estimated for all 28 pairs of loci (from eight loci) in 81 populations of Quercus petraea spread over the natural distribution of the species. Significant disequilibria were found in almost all populations for two pairs (Aap-A/Lap-A, Mr-A/Dia-A) that have also shown strong linkage in cosegregation analysis. These pairs belong to the so-called complex loci producing nearly identical gene products and that are tightly linked. Significant disequilibria were also found for other pairs of loci that are linked to a smaller degree. The amount of disequilibrium followed a geographical pattern. The number of pairs showing significant disequilibria per population was higher on the edges of the natural range (Norway, Great Britain, Turkey). Disequilibria for the two pairs (Aap-A/Lap-A, Mr-AIDia-A) were also higher at the edges of the distribution and were correlated with longitude. Population differentiation resulting from the associations of alleles at different loci was increased when the correlations of allele frequencies at the within-and between-population level were of different magnitude. It is suspected that correlations at the between-population level may arise from historical causes rather than gametic disequilibrium. Finally, the first canonical variate (multivariate score) including allelic frequencies of all eight loci follows a strong longitudinal pattern of variation.

Genetic variation of oaks (Quercus spp.) in Switzerland. 3. Lack of impact of postglacial recolonization history on nuclear gene loci

“…Kremer and Zanetto 1997;Petit et al 2002). Restricted gene flow through seeds, but extensive gene flow through pollen, are likely to be the main causes of the contrasting patterns of genetic differentiation of maternal and biparental gene markers in oaks (Ennos 1994).…”

Genetic variation at allozyme and RAPD loci in sessile oak Quercus petraea (Matt.) Liebl.: the role of history and geography

“…Species found in Spain (genera Pinus and Quercus) would indicate a drier climate than in South Italy and Greece (where Pinus and Quercus, but also Corylus, Fagus, Fraxinus, Tilia and Ulmus were found). The concordance of patterns at the two loci Aap and Lap can be attributed to high levels of disequilibrium between them (Kremer & Zanetto 1997). This linkage is both genetical and functional, the two allozymes being involved in the same biochemical pathway, peptides hydrolization (Müller-Starck et al 1996).…”

Gene flow and natural selection shape spatial patterns of genes in tree populations: implications for evolutionary processes and applications

“…To identify the regions of conservation importance for valley oak, we used a multivariate approach that we had previously used to analyze the environmental correlations with geographic patterns of genetic variation in Missouri Ozark forests Sork 1999, 2001). Multivariate models, such as canonical correspondence analysis (CCA), are useful because they detect small genetic differences across loci that reveal cumulative patterns of differentiation that are not apparent with analyses of one locus at a time (Conkle and Westfall 1984;Kremer and Zanetto 1997) and provide signatures of genetic differences that can be correlated with environmental gradients or associated with geographic regions. In one study, we used the multilocus genotypes of valley oak as indicators of unique genetic composition and demonstrated how one could design a reserve network to maximize the preservation of unique genetic diversity for the species ).…”