UBC Theses and Dissertations

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UBC Theses and Dissertations

Climate variability and stress exposure alter evolutionary responses across populations of Mimulus cardinalis Branch, Haley Anne


We are just beginning to understand population-level responses to extreme climatic events. Populations of the same species from differing climatic regions can have different traits and adaptations that have locally evolved, and this can alter their evolutionary trajectories when exposed to similar selection pressures. My thesis examines how populations of Mimulus (Erythranthe) cardinalis (scarlet monkeyflower) from historically different climates respond to a severe drought, using a resurrection approach to grow ancestral (pre-drought) and descendant (peak-drought) individuals in a common environment and growing them in either wet or dry treatments. In chapter two, I report that populations in the north (historically wetter and less variable) did not show evolutionary changes at the macro-morphological scale (e.g., date of flowering, specific leaf area), while southern populations (historically drier and more variable) evolved toward trait values that promote dehydration avoidance. In chapter three, I find that macro-morphological changes (or lack thereof) can be better understood by examining more cryptic micro-morphological alterations in leaf architecture and physiology. Here, northern populations evolved greater plasticity in mesophyll composition, stomatal density and assimilation rate, trending toward dehydration avoidance and potentially allowing macro-morphological traits to remain stabilized. Southern populations began with trait values that were more drought avoidant and evolved further along this trajectory, resulting in a trade-off for photosynthesis under wet conditions. Finally, differences in evolutionary trajectories between northern and southern populations can also be attributed to phenotypic legacies from non-genetic inheritance. In chapter four, I grew northern and southern populations for 3 generations under either wet or dry treatments to assess epigenetic stress memory. Northern populations exhibited greater epigenetic-attributed plasticity than the southern populations, but the southern populations evolved epigenetic plasticity, which likely assisted in vegetative avoidance of drought. Thus, although at the macro-scale northern populations did not show a clear trend, anatomical features and grandparental histories show both regions rapidly evolve toward dehydration avoidance and non-genetically respond to drought stress, but through different mechanisms. These results indicate that northern populations are becoming more like ancestral southern populations, while southern populations might be nearing the edge of their adaptive capacity.  

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