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Ecological genetics and effects of inbreeding and white pine blister rust on genetic structure of whitebark pine (Pinus albicaulis Engelm.) Bower, Andrew David


In this thesis I investigate the ecological genetics of whitebark pine (Pinus albicaulis Engelm.), a five-needle pine found near treeline in western North America. Throughout its range whitebark pine is experiencing declines due to the introduced disease white pine blister rust and successional replacement due to fire suppression. Conservation and restoration efforts are needed to reverse this decline; however, little is known about the genetics of whitebark pine as related to quantitative traits. A common garden experiment was used to assess rangewide genetic variation and geographic differentiation of quantitative traits. Significant variation among provenances was detected for all traits except spring cold injury. Geographic differentiation was weak to moderate for growth and biomass traits, but was strong for fall cold injury and date of needle flush. Both of these variables were significantly associated with mean temperature of the coldest month at of source location. These results were used to determine guidelines for seed movement in whitebark pine management and restoration. Isozyme analysis of seed tissues was used to determine the mating system and presence and strength of inbreeding depression in quantitative traits. Regional estimates of outcrossing rate (tm) ranged from 0.73 to 0.93, with a mean of 0.86. Family mean tm values were skewed towards outcrossing; however, some individuals experienced substantial inbreeding. Biomass in the southern B.C. region was the only trait and geographic origin with significant inbreeding depression, and is predicted to be reduced by 19.6% in this region. Isozyme analysis of bud tissue was used to determine genetic diversity (Ho and He) and fixation index (Fis) for three age cohorts, from 14 sites. Significant evidence of inbreeding (Fis>0) was found in all age cohorts. When sites were stratified by level of blister rust infection, differences in Fis and Ho among cohorts were only significant when level of infection was low. A significant negative association with level of rust infection was found for Ho only in the mature cohort. This suggests that when differential selection due to rust is weak, more heterozygous individuals are favoured. However, more homozygous individuals appear to have higher fitness when rust infection levels are high.

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