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Genetic variation, population structure and mating system in bigleaf maple (acer macrophyllum pursh) Iddrisu, Mohammed Nurudeen


Ecological characteristics and life history traits of long lived woody plants influence their levels of genetic variation. To embark upon sound management, utilization and conservation of plant species, a thorough understanding of genetic processes affecting their persistence is essential. In this thesis, I studied genetic diversity, population structure, and mating system as well as compared genetic diversity and inferred differences in genetic processes in continuous versus fragmented populations of bigleaf maple (Acer macrophyllum Pursh). Bigleaf maple is one of the most abundant hardwood species in the Pacific Northwest and its native range extends from latitude 33° N to 51° N along the Pacific coast of North America. Genetic diversity, estimated using isozyme markers, revealed a mean expected heterozygosity (H[sub E]) of 0.152 similar to other North American angiosperm trees. The level of population differentiation was moderately low (F[sub ST] = 0.054), indicating extensive gene flow among populations. Estimated outcrossing rates in two populations were high (95%) but significantly less than one, with no biparental inbreeding evident. A relatively high level of correlated matings was found, consistent with 2-5 effective pollen donors per tree, indicating low adult density and limited pollinator dispersal. Seedling and adult populations possess similar levels of genetic variation regardless of whether populations are fragmented or continuous. However, seedling cohorts have higher levels of inbreeding than adult cohorts, on average, in both continuous and fragmented populations. Analysis of spatial genetic structure indicates non-random distribution of genotypes in all three fragmented populations and one of the three continuous populations. I found a significant positive autocorrelation (p[sub ij]= 0.20) among individuals located up to 100 m apart in all three fragmented populations and among individuals located at approximately 100-200 m apart (p[sub ij] = 0.14) in one of three continuous populations. Finally, for quantitative traits, provenances and families within provenances showed significant genetic variation for height growth and bud flush traits, but not for diameter growth. Individual heritabilities for all traits were generally low to moderate (0.15-0.21), and family heritability was higher only for bud flush. Comparison of Q[sub ST] and F[sub ST] in this study (mean Q[sub ST]= 0.17 > mean F[sub ST]= 0.09) suggests the involvement of selection for different phenotypes in different populations of bigleaf maple.

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