Title: Essays in Evolutionary Theory
Abstract: In my thesis defense, I will talk about chapters 8 and 9. Chapter 1 proposes and empirically tests a model for the evolution of long, synchronous flowering intervals in bamboos. Chapter 2 develops a mathematical method for studying the interaction of multiple populations in stochastic evolutionary games. Chapter 3 applies this methodology to antagonistic and mutualistic species interactions, showing that faster evolution is beneficial in antagonisms, but that slower evolution can be beneficial in some mutualisms. Chapter 4 uses a stochastic model of evolutionary games to show that assortment favors the evolution of cooperation under very general conditions, including when Hamilton's rule fails. Chapter 5 uses a simple model and economic intuition to show that the Trivers-Willard hypothesis of sex allocation—mothers in good condition should (i) have more sons and (ii) care more for sons—holds more generally in case (i) than in case (ii). Chapter 6 identifies and mathematically characterizes a novel selective force, induced by genetic drift, operating in transitions between male and female heterogamety. This 'drift-induced selection' favors epistatically dominant sex determining mutations, perhaps explaining their observed preponderance. Chapter 7 proposes a model to explain the rarity of environmental sex determination (ESD) relative to genetic sex determination (GSD), based on the inevitable coupling of sex-biasing alleles (e.g., of genes underlying temperature thresholds) and 'sexually antagonistic' alleles (which increase fitness in one sex but reduces fitness in the other). Chapter 8 proposes and implements a new metric for genome-wide recombination, r̄, that takes into account crossover positions and independent assortment of homologs. Chapter 9 discovers a deeply-conserved form of crossover patterning: the number of crossovers covaries positively across the chromosomes within individual meiotic nuclei. Crossover covariation substantially increases the variance of total crossover number per nucleus, and thus increases the frequencies of gametes with either very many or very few crossovers, which population genetic modelling shows to be advantageous in a fluctuating environment.
Committee: Martin Nowak (Advisor), David Haig, Daniel Hartl, Nancy Kleckner (MCB), Naomi Pierce