The interaction of selection, pleiotropy, and drift in phenotypic evolution

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Evolution of the traits of organisms most famously occurs through natural selection, but can also occur through other processes. Traits can evolve through genetic drift, especially in small populations, when individuals may die or fail to reproduce for reasons having nothing to do with their fitness. Traits can also evolve as a result of pleiotropy, in which single genes affect multiple traits. If natural selection acts to change one trait, other traits that share pleiotropic genes with it will also evolve. While selection, drift, and pleiotropy have been well-studied in isolation, rarely have the roles of all three been considered together. This research will comprehensively determine the roles of natural selection, drift, and pleiotropy in a plant species that shows patterns of recent evolutionary change across latitudes and altitudes. Examining these factors simultaneously will help us understand how organisms can adapt or fail to adapt to environmental change. The project will integrate field studies of selection with laboratory genetics and genomics. It will involve teams of K12 teachers and undergraduate students from underrepresented groups, improving their understanding of the process of science and scientific careers, as well as producing classroom curricular materials based on the data.This project builds upon decades of field and laboratory research with the model plant species Arabidopsis thaliana. The recent evolution of self-fertilization in this species has weakened natural selection on stamen number because short stamens do not contribute to seed production. Short stamens have been lost in some populations of this species, especially at low altitudes and latitudes. Three gene regions associated with stamen loss have been identified, permitting simultaneous investigation of evolution at the morphological and genomic levels. The role of natural selection in stamen loss will be evaluated using field and growth chamber experiments with plants of known genotypes. The role of pleiotropy will be evaluated by statistical associations between stamen loss and other traits known to be affected by selection, and by studying genomic associations for gene regions influencing these traits. Finally, the role of drift will be evaluated by studying whole-genome diversity and assessing the relationship between small population size and stamen loss.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.