Selection, mutation and evolution in plant populations

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Evolutionary biology seeks to understand the processes underlying the diversity of life on earth. All current diversity—whether among phyla, species or individuals—originated as mutations within populations. The fitness effects of new mutations and their rate of appearance are two of the most important quantities in evolution because they affect evolutionary rates, standing genetic variation and the advantage of other features such as the rate of inbreeding. The research proposed here will address fundamental questions concerning the causes and consequences of mutation in plant evolution. Most species of seed plant possess both male and female sexual organs and therefore experience selection on the rate of self-fertilization. The mating system in turn influences standing genetic variation and long-term population persistence. Although this topic has generated a rich body of theory, experimental tests lag far behind. In particular, we still do not understand why so many populations are partially self-fertilizing. We have previously proposed that the number of self-fertilized offspring may often be correlated with the number of offspring produced as both mother and father by outcrossing, and that these correlations will maintain mixed mating. Using recently developed molecular tools, we will test model predictions in natural populations of a partially self-fertilizing plant. Using genetic models and high-performance computing, we will investigate how correlations among fitness components, generated by pleiotropic mutation, affect the long-term evolution of selfing rates. The second major area of proposed research investigates sex biases in mutation transmission to offspring. It has been known for several decades that animal species often exhibit male-biased mutation. Earlier work in our lab discovered that male-biased mutation transmission also exists in both gymnosperms and angiosperms. The cause of the bias in plants, however, remains a mystery. We will test the hypothesis that the higher number of cell divisions in the production of pollen compared to female gametophytes causes the male bias by studying rates of molecular evolution in gymnosperms. We will use confocal microscopy to test whether experimentally induced mutations are more strongly selected against in female than in male gametophytes in a flowering plant. We will test whether mutagenesis causes epigenetic changes that are more deleterious to surviving offspring when transmitted through sperm than through egg. The research proposed here aims to advance our understanding of the combined roles of selection and mutation in shaping plant evolution. The projects provide modern and advanced training opportunities at both the graduate and undergraduate levels in several areas including bioinformatics, computer-based simulation, confocal microscopy, statistical analysis and techniques in field biology.