NATURAL SELECTION, POPULATION GENETICS, AND TRAIT DIVERSIFICATION OF SILENE STELLATA AND ITS POLLINATING SEED PREDATOR HADENA ECTYPA
Dudash, Michele R
Fenster, Charles B
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My dissertation explores four aspects of the interaction system consisting of the hermaphroditic plant Silene stellata and its pollinating seed predator Hadena ectypa in a community context. My overarching goal is to deepen our understanding of the selection dynamics influencing floral evolution of hermaphroditic plants. First, I characterized the mating system of S. stellata to evaluate its role on floral evolution of S. stellata and the Silene-Hadena interaction. Second, I compared the spatial genetic structures of S. stellata and H. ectypa to evaluate any discrepancy in their dispersal abilities. Third, I addressed whether selection pressures on floral traits of S. stellata differ between sexual functions and between pollinator types. Last, I quantified the genetic basis of the Silene floral traits to predict evolutionary response under complex selection scenarios. In Chapter 1, I found the study S. stellata population to be predominantly outcrossing with short pollen dispersal distance. The lack of effect of pollinator types (specialized seed predator and other nocturnal copollinating moths) on S. stellata mating system parameters suggests that the dual pollinator type relationship with S. stellata is stable and perhaps contributes to the persistence of the plant species. In Chapter 2, I found no genetic differentiation among the Hadena populations, while the Silene populations showed strong spatial structure. This suggests that pollen flow between Silene populations rarely co-occurs with moth movement. This asynchrony in gene flow could potentially stabilize the interaction dynamics and prevent strict local coadaptation. In Chapter 3, I found conflicting selection pressures between male and female reproductive functions of S. stellata. Strong selection through female function was detected to avoid fruit predation, while competition for mates through male function provides a counterbalancing force potentially contributing to the long-term maintenance of this interaction. In Chapter 4, I found intermediate heritability and prevalent positive genetic correlations between Silene floral traits, suggesting the Silene population is capable of responding to phenotypic selection on its floral design, while the abundant genetic correlations could also pose certain constraints on trait divergence. My results suggest that floral evolution is governed by complex, interdependent processes and that the Silene-Hadena interaction could be maintained through the dynamical balance between various opposing evolutionary forces.