Selection and genetic constraints on clonal investment in a perennial plant

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Steinecke, Christina
Clonality , Life history , Artificial selection , Quantitative genetics , Evolution , Mimulus guttatus
Many plant species can reproduce both clonally and sexually. Why, then do some plants invest resources into both? The relative importance of the two modes of reproduction likely varies in different ecological conditions. The ability for selection to drive different investment strategies will depend on phenotypic variation and genetic constraints between the two modes of reproduction. Genetic correlations between traits can either facilitate or constrain evolutionary responses depending on the direction and strength of selection. Here, I use an artificial selection experiment to investigate the capacity for clonal investment to respond to high or low truncation selection in perennial Mimulus guttatus. The aims of my research are to quantify the standing variation and heritability of clonal reproduction, and then to estimate the magnitude of phenotypic responses to artificial selection on clonal growth and identify genetically correlated traits. To address these aims, I established an outbred population from field collected seed in a greenhouse, then imposed four generations of divergent, truncation selection on clonal growth for two replicate high lines, two low lines, and a control line. I used quantitative genetics to investigate additive genetic variance, heritability, and the response of clonal growth through time. I investigated how genetic correlations in life history traits measured throughout the lifecycle might constrain evolutionary trajectories. My results showed that selection elicited the predicted divergent response in clonal growth; however, high clonal lines respond more strongly to selection compared to low clonal lines. I found that selection did not drastically change investment strategies but did affect trait means among selection lines. These findings suggest that populations have greater capacity to increase clonality in the face of selection, and that selection on an increase in clonal investment might be more straightforward. This study tests a classic, yet unresolved, evolutionary question and suggests populations harbour sufficient standing genetic variation to respond rapidly to selection and that the underlying genetic architecture and trait covariation could constrain evolutionary trajectories and adaptive divergence.
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