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UBC Theses and Dissertations

Eco-evolutionary perspective on life-history traits with special emphasis on seed dormancy and its genetic basis of adaptation in conifers Liu, Yang


Life-history traits, known as fitness components, are related to the timing and success of development, reproduction, and senescence throughout the life cycle. Selection in variable environments may favor plants to defer germination until suitable conditions occur. Seed dormancy is an innate constraint on germination timing and prevents germination during periods that are ephemerally favorable. The timing of seed germination is the earliest life-history trait that is expressed and sets the context for the traits that follow. As such, seed dormancy may be construed as an adaptation for survival during bad seasons and can exert cascading selective pressures on subsequent life stages. Seed size is another important life-history trait linking the ecology of reproduction and seedling establishment with that of vegetative growth. As the two traits are, at modulations, regulated by hormone signaling cascades, evolve under correlated selective pressures, and exhibit co-varying phenotypes, this dissertation intended to elucidate their eco-evolutionary dynamics and possible genetic basis of adaptation. From an eco-evolutionary perspective, I demonstrated that dynamic climatic variables rather than constant geographic variables are the true environmental driving forces in seed dormancy and size variations in Pinus contorta Dougl. Evapotranspiration and precipitation in the plant-to-seed transition are the most critical climatic variables for seed dormancy and size variations, respectively. Unlike random temperature fluctuations between generations, wide temperature shifts considerably alter population structures and accelerate life-history evolution. Regarding the genetic basis of adaptation, environmental cues trigger different seed-set programming in Picea glauca and Arabidopsis by employing lineage-specific and deeply conserved microRNAs at different expression levels, respectively, to entrain phenotypical variations, such as dormancy intensities. Our findings additionally point to auxin as a key player that likely works in conjunction with the ABA and GA signal pathways previously investigated in mechanisms underpinning the seed-to-plant transition by chilling in Picea glauca seeds. This dissertation increases our understanding of plant evolution and persistence in the context of climate change and provides fundamental insight for understanding how microRNAs are at play in seed-set programs to regulate phenotypes, how winter chilling contributes to the timing of phenology, and how conifer life histories may develop under new climate scenarios.

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