|Department:||Faculté de foresterie, de géographie et de géomatique|
|Keywords:||Foresterie et géodésie|
|Full text PDF:||http://www.theses.ulaval.ca/2015/31278/31278.pdf|
The phylogeographic structure and postglacial history of balsam fir (Abies balsamea) were inferred using mitochondrial DNA (mtDNA) and chloroplast DNA (cpDNA). Population differentiation was high for both mtDNA (dispersed by seeds only) and cpDNA (dispersed by both seeds and pollen), implying a more restricted pollen gene flow in balsam fir than usually observed for other boreal conifers. Reduced pollen dispersal due to its structural properties and the recurrence of spruce budworm outbreaks limiting the reproductive effort of balsam fir are likely related to this trend. Polymorphisms from the mtDNA and cpDNA genomes were geographically structured, indicating the existence of at least five genetically distinct glacial lineages. The concordance between mtDNA and cpDNA lineages was not complete, reflecting restricted but nonetheless detectable cpDNA gene flow between lineages since the Holocene recolonization. New cpDNA and mtDNA genome combinations resulting from this recent gene flow and cytoplasmic genome capture were also observed. Studying the extent and direction of cytoplasmic introgression is useful to unravel the dynamics of hybrid zones between interbreeding species. The extent of cytoplasmic introgression in the Abies lasiocarpa x Abies balsamea species complex was characterized using markers from the mitochondrial (mtDNA) and chloroplast (cpDNA) genomes. Hybrid zone dynamics since postglacial colonization was inferred by assessing the concordance between current and historical locations of the hybrid zone using genetic and paleoecological data. Interspecific gene flow was higher for cpDNA than mtDNA markers and the geographic distribution of mitotypes was thus more congruent with species distributions than chlorotypes. This genetic signature was contrary to expectations under a moving hybrid zone scenario, as well as empirical observations in conifers. Genetic evidence for a stable hybrid zone was corroborated by the colonization chronology derived from published fossil data. While cpDNA interspecific gene flow seemed primarily driven by westerly winds, non-neutral factors may also play a role in maintaining of this complex yet stable hybrid zone.