From Genes to Stasis

A great challenge that biology faces is in integrating phenomena from different scales. On the micro scale of the spectrum, we can measure subcellular processes, like gene expression and regulation. On the macro scale, we can measure species level variation, ecological interactions, and the like. The challenge biology faces is in following the causal threads that lead individuals, populations, and ultimately, species to the variation in traits that we see in nature. The idea that there are cascades of causality that reduce to a microscopic scale is often referred to as the Genotype to Phenotype map (Houle and Govindaraju 2010). The Genotype to Phenotype map is ultimately a problem of measurement; what do we need to measure at each scale of interest in order to understand and, more importantly, predict variation elsewhere on the spectrum? This thesis is focused on two parts of the genotype-phenotype spectrum. The first chapter focuses on the macro scale, specifically on how traits maintain stasis across species. Here we use Drosophila melanogaster wing shape as a model to test whether stasis is explained by constraint or by stabilizing selection. We test for constraint with an artificial selection experiment on wing shape. We then test for stabilizing selection by measuring flight differences among selected and unselected flies and by testing for mate preference. In the second chapter, I focus on the micro scale by describing a method to measure the spatial properties of gene expression patterns. Quantitative measures of gene expression currently focus on mutations in the genome and/or the magnitude of expression. This ignores the spatial components of gene activity that are critical in the formation of pattern and the maintenance of growth during development. I describe methods to measure the spatial characteristics of genes that form discrete and continuous patterns of expression. I then give three examples of the method by quantitatively disrupting three genes and estimating the effects on a discrete and a continuous expression pattern.