A multivariate analysis of introgression betweenQuercus roburandQ. petraeain The Netherlands

Abstract

Hybridization and introgression between Quercus robur and Q. petraea was investigated in 12 Dutch populations, using multivariate analysis. Compared with the reference groups, the differences between the two taxa are slight, but distinct. The Q. petraea types differ more from their reference group than the Q. robur types, possibly due to greater selection pressure. In most populations a range of specimens occurs between pure Q. robur and pure Q. petraea. The latter category is poorly represented, and actual F,-and F 2-hybrids are most uncommon. Products ofintrogression between primary hybrids and Q. robur as well as Q. petraea constitute an important part of the populations. Hybridization and introgression is partly due to planting of Q. robur by man. In the natural population of the Meinweg a gradient is established between Q. robur in the lower, moist levels and Q. petraea in the higher, relatively dry levels.

Leaf morphological differentiation between Quercus robur and Quercus petraea is stable across western European mixed oak stands

“…As a result, among the three statistical methods tested, CDA provided slightly more congruent results between the global and local analyses (table V). These results were comparable with other investigations using multivariate analysis conducted in various parts of western Europe ( [14] in the central part of France; [12] in the eastern part of France; [15] in the Netherlands), central Europe ( [1] in Germany and Poland) and eastern Europe [8], although they differed in their sampling strategy. All these case studies also showed a strong bimodal distribution of the synthetic variables.…”

“…An alternative way would have been to include additional diagnostic characters available for taxonomic identification. In a number of different reports intermediate phenotypes have received special attention, first by delineating a specific class of intermediate phenotypes in comparison to reference populations [13,15,30] and then by designating these trees as introgressed forms. Natural hybridization has been shown by mating system analysis with gene markers in natural mixed populations [5,21].…”

“…Dendrologists require classification criteria for taxonomic purposes [3,17,18,22,25]. Forest biologists and ecologists seek unambiguous traits which could be used for studying introgression between these two interfertile species [15,28,29,34]. The vast amount of literature devoted to morphological variation in mixed oak stands demonstrates the debate that has been raised.…”

Comparison of morphological characters and molecular markers for the analysis of hybridization in sessile and pedunculate oak

“…They present slight differences in a series of morphological characters. The differences in the characters of the leaves and seeds are usually used in the literature to discriminate between the two species (Gardiner, 1970;letswaart and Feij, 1989). Interspecific gene flow between sessile and pedunculate oak has been inferred in many studies on the basis of the finding, in natural mixed populations, of trees with intermediate morphology (Rushton, 1978(Rushton, , 1979Minihan and Rushton, 1984;Semerikov et al, 1988;letswaart and Feij, 1989).…”

“…The differences in the characters of the leaves and seeds are usually used in the literature to discriminate between the two species (Gardiner, 1970;letswaart and Feij, 1989). Interspecific gene flow between sessile and pedunculate oak has been inferred in many studies on the basis of the finding, in natural mixed populations, of trees with intermediate morphology (Rushton, 1978(Rushton, , 1979Minihan and Rushton, 1984;Semerikov et al, 1988;letswaart and Feij, 1989). Hypothesis of hybridization between these two species is supported by the success of interspecific controlled crosses (Rushton, 1977;Aas, 1991;Steinhoff, 1993 (Bacilieri et al, 1996) (Roberts and Hiorns, 1965;Elston, 1971 166,195,204,206,210,240,241,323,342,396 20,23,26,29,32,33,35,36,37,39,40,41; DFAc).…”