Evolutionary Analyses of Genomic Imprinting and Other-Regarding Motivations

This dissertation applies population genetic and evolutionary theory to two separate topics: the evolution of genomic imprinting and the evolution of other-regarding motivations. In the first three chapters, I explore how genomic imprinting, a molecular mechanism by which the expression of an allele depends on the sex of the donating parent, might have evolved and some of the consequences imprinting might have for genetic diversity within populations. The last chapter presents a framework to study how a motivation to help others, a so-called other-regarding motivation, can evolve and suggests how such motivations might be modeled and quantified. Chapter 1 explores the effect of sex-specific selection and allelic dominance on the evolution of genomic imprinting. A two-locus evolutionary model is presented in which a second locus modifies the imprinting status of the primary locus, which is under differential selection in males and females. A modifier allele that imprints the primary locus invades the population when the average dominance coefficient among females and males is greater than 1/2 and selection is weak. The condition for invasion is always heavily contingent upon the extent of dominance for any strength of selection. Imprinting is more likely in the sex experiencing weaker selection only when the average dominance coefficient is 1/2. In chapter 2, we investigate the evolution of genomic imprinting in a subdivided population. In particular, we are interested in whether the prediction of the kinship theory for the evolution of genomic imprinting holds in a subdivided population and what demographic or genetic features might alter that prediction. The kinship theory posits that a trade-off between maternal fertility and offspring survival can drive the silencing of gene expression from alleles that result in increased offspring survival when those alleles are inherited from the mother and when females mate with more than one male. We that find this prediction holds when the population conforms to the infinite island model of population structure and for any amount of migration and any local deme size. In addition, allelic dominance and sex-specific affects on offspring survival do not alter this prediction. The model also reveals that imprinting can evolve in unexpected ways when the demography of the population is more complicated. The final chapter on genomic imprinting, chapter 3, studies the effect of imprinting on the dynamics of genetic diversity within a single population. Generally, complex genotype-frequency dynamics are uncommon in simple population-genetic models. When genotype-frequency cycling does occur, it is most often due to frequency-dependent selection that results from individual or species interactions. In this chapter, we show that fertility selection and genomic imprinting are sufficient to generate a Hopf bifurcation and complex genotype-frequency cycling in a single-locus population-genetic model. Previous studies have shown that on its own, fertility selection can yield stable two-cycles but not long-period cycling characteristic of a Hopf bifurcation. Genomic imprinting allows fitness matrices to be nonsymmetric, and this additional flexibility is crucial to the complex dynamics we observe in this fertility selection model. Additionally, we find under certain conditions that stable oscillations and a stable equilibrium point can coexist. These dynamics are characteristic of a Chenciner (generalized Hopf) bifurcation. We believe this model to be the simplest population-genetic model with such dynamics. Although much previous work describes evolutionary mechanisms that promote or stabilize...