Etude moleculaire du complexe d'especes Picea mariana - Picea rubens.

摘要

The aim of this study was to better understand natural hybridization and estimate the genetic divergence in the species complex composed of black spruce (Picea mariana B.S.P [Mill.]) and red spruce ( P. rubens Sarg.). These questions were investigated at the molecular level. Species specific genetic markers to black spruce and red spruce have been developed using typical morphological trees to each species, in order to improve the capacity of detecting interspecific genetic exchanges. Populations were sampled in both areas of allopatry and in the area of sympatry located in the province of Quebec. Every trees were validated at the morphological and molecular levels, and then classified as black spruce, red spruce or hybrid/introgressant. Furthermore, the genetic diversity of each species was estimated at the nuclear gene level using parental type individuals validated with molecular markers. During the development of species specific markers, most of the genetic fragments observed were shared by the two species. Three markers specific to black spruce and four markers specific to red spruce were identified from more than 600 DNA fragments. The analysis of allopatric populations indicated a low rate of introgression. However, a larger proportion of hybrid/introgressant trees was observed in the area of sympatry, suggesting a low level of reproductive isolation between black spruce and red spruce. As expected, molecular markers were more sensitive than morphological characters for detecting hybrid/introgressant trees in natural populations. The hybrid zone was broad and some populations were dominated by hybrid and introgressant individuals. Based on all analyses, the genetic similarity was high between the two species, but red spruce was genetically depauperated as compared to black spruce. The genetic variability of red spruce appeared to be a subsample of the one present in black spruce, suggesting a progenitor-derivative relationship in this species complex.