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Quantitative trait variation in Limber Pine (Pinus flexilis) Gass, Barb

Abstract

Limber pine (Pinus flexilis) is one of the North American white pines under duress. Pressured by several forces including an introduced fungal pathogen (Cronartium ribicola) and changing climate, this is a species of conservation concern in many regions. The ability to adapt to shifting conditions depends on the amount and distribution of standing genetic variation. To evaluate the patterns and extent of variation in limber pine, I examined needle traits with regards to pathogen infection, and the distribution of quantitative traits in the context of climate. Specifically, I measured how leaf traits differ after surviving an inoculation with C. ribicola and found that survivors of infection had significant differences in needle size, stomatal density and specific leaf area compared to uninoculated controls. In addition, the variance of each trait shifted modestly, pointing to signs of both phenotypic selection and plasticity. Next, I examined the structure of quantitative genetic variation across 16° of latitude by phenotyping traits in a common garden experiment. This trial revealed that population differences explained between 1-24%, and family between 1-20% of the total phenotypic variance, depending on the trait under inspection. This corresponded to a mean Qst estimate of 0.158 (range 0.02-0.19), with growth traits exhibiting the greatest population differentiation. Precipitation-related climate variables were the strongest predictors of differences among populations. These results suggest that limber pine has relatively low levels of quantitative genetic variation among populations, but an almost equivalent amount within populations. Whether or not it will be sufficient to cope with the many stresses this species contends with remains unclear.

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