|Publication Type:||Journal Article|
|Year of Publication:||1993|
|Authors:||R. J. Petit|
|Journal:||Annals of Forest Science|
This contribution reviews studies of nuclear and organelle gene diversity in oak species. Studies of allozymes were reported for 33 species belonging to the sections Erythrobalanus, Lepidobalanus and Mesobalanus of the genus Quercus. The extent and organization of gene diversity were investigated at 3 hierarchical levels: complex, species and population. Total diversity at the species and population level varies greatly among species (from 0.06 to 0.40). The range of variation among species is as large as that observed in other plant genera. Life history characteristics and evolutionary history are the main explanations for these results. Species with large and continuous distributions such as Q petraea and Q rubra exhibit high levels of gene diversity. Within a complex, most of the nuclear gene diversity is distributed within populations (74%). The remaining diversity is mainly due to species differentiation (23%), while the between-population component is low (3%). Organelle gene diversity has been investigated recently in 2 species complexes in the section Lepidobalanus (one in North America and one in Europe). Compared to nuclear genes, organelle gene diversity is strikingly different. Contributions of within-stand variation, species differentiation and population differentiation to total diversity, are respectively 13%, 11 % and 76%. Trees of a given population generally share the same chloroplast genome. Moreover, trees of different species (with reported introgression) occupying the same stand exhibit a high degree of similarity.