Models Incorporating Genetic Variation

Genetic variation is a dominant feature in the study of evolution. The presence of variation is embedded at every level, from a single individual all the way to different species. Understanding the mechanisms that allow variation to be introduced and maintained is crucial to our understanding of nature. If empirical data and observations provide the substrate needed for such understanding, the role of theory is instead to train our intuition and help experimenters in formulating testable hypotheses. Here I use mathematical modeling as a tool to investigate the effects of genetic variation at different levels. I begin by looking at variation expressed at the level of an individual. Enzyme isoforms are a pervasive presence in many species. They can be produced by different genes, different alleles or by alternative splicing of a single gene. I examine the potential benefit provided by the presence of enzyme isoforms in the Drosophila circadian rhythm. I show that controlling isoform proportion can be a powerful mechanism to reduce the effects of variations in the values of system parameters, thereby increasing system robustness. My second research project looked at genetic variation at the population level. Gamete recognition proteins are central to reproduction. They determine gametic compatibility both within and between species. In marine broadcast spawners an astonishing number of variants have been found for these proteins. The mechanism responsible for this variation is thought to be sexual conflict. This conflict arises because each sex has different and opposing interests at fertilization. I investigate how sexual conflict and spawning behavior can drive the evolution of recognition protein polymorphism and promote gametic disequilibrium by assortative mating. I conclude by looking at variation at the species level. Marine broadcast spawners need to synchronize the release of their gametes to increase the chance of successful fertilization. Highly synchronized gamete release can result in polyspermy. Polyspermy is the fusion of multiple sperm with a single egg at fertilization, making an unviable zygote. A possible strategy to avoid polyspermy is to shift spawning time. I show how a population where spawning time is the phenotype under selection can split in two reproductively isolated populations in sympatry.