THE GENETIC DETERMINANTS OF POPULATION-LEVEL RESPONSES TO ENVIRONMENTAL CHANGE: TESTS IN THREE PLANT SPECIES

Shelby L. Tisinai

doi:10.7273/000007483

A major goal of evolutionary biology is to predict how organisms will respond to future environments. Predicting these evolutionary trajectories is often accomplished by looking for patterns of genetic variation left by past evolutionary forces, revealing evolutionary histories (e.g., founder events, degrees of connectivity) illuminating how populations may respond to future environments. Above all, there must be sufficient standing genetic variation for a population to evolve and continuously form new combinations of alleles necessary to meet the demands of novel environments. Second, evolutionary histories shape current population structures and offer signposts for future evolutionary trajectories. Environments therefore not only shape extant patterns of genetic variability and structure — they also provide a means to justify important determinants of fitness. The aims of this dissertation are to (i) characterize the genetic diversity in plant species endemic to steep elevation gradients in relation to past environments and (ii) evaluate possible future evolutionary trajectories given potentially adaptive patterns of genetic diversity. These two broad aims are achieved, with varying degrees of integration, in three dissertation chapters. First, we show that, after six generations and despite severely reduced genetic variation, a highly-selfing population of Mimulus guttatus shows small but significant responses to strong selection imposed on stigma-anther distance, a morphological trait related to breeding strategy (i.e., selfing or outcrossing). Second, we assessed the influence of elevation on population structure and signatures of adaptation within six populations of Cardamine cordifolia. Here, we found that low genetic variation among all study populations likely stems from a history of panmixia; future responses among all populations are likely to be the same, though may ultimately result in opposing fitness outcomes. Third, we used gene expression differences among five populations of Boechera stricta to test the influence of stark climatic gradients that are strongly correlated with elevation on signatures of adaptation. In this study, we found that there were differentially expressed genes among the populations that coincided with elevation. Functional enrichment of differentially expressed genes revealed that these genes were related to important environmental variables that are correlated with elevation. Altogether, the results of this dissertation highlight the utility of investigating patterns of genetic variation to hone predictions of population response to future environments.

THE GENETIC DETERMINANTS OF POPULATION-LEVEL RESPONSES TO ENVIRONMENTAL CHANGE: TESTS IN THREE PLANT SPECIES

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