Unbiased genetic dissection of widely observable phenotypic traits in the wild has
long been the goal of evolutionary geneticists. Mice, bacteria, rice and stickleback fishes
have historically been among the prime model organisms in the field. Here, we leverage
the recent surge of Saccharomyces yeast as a model genus in ecology and evolution to
begin answering questions about the genetic basis of ancient trait differences that have
evolved between species, over long evolutionary time scales. Specifically, we want to
know what genetic mechanisms evolution has used to create new traits in the distant
past, and what biological functions have been the focus of adaptation in the past. I
introduce the field and our questions of interest in the introductory Chapter 1. Next,
Chapter 2 delves deeper into the methods that have been used in the past to dissect
interspecies genetics, reviewing the literature and drawing general conclusions from
what we have learned so far. In Chapter 3, we develop a new application of the
reciprocal hemizygote test on a genome-wide scale to drill down to the single gene level
and dissect the ability of S. cerevisiae to grow at high temperatures relative to other
Saccharomyces species. We uncover a suite of housekeeping genes genetically
responsible for this derived phenotype and reveal a likely defect in cell division in S.
paradoxus as the culprit for cell death at high temperatures. Finally, in Chapter 4, we
investigate two more species-specific differences: 1) resistance to the drug benomyl, a
microtubule poison and 2) cold tolerance. Unexpectedly, while microtubules are the
molecular target of benomyl, it is the genes encoding water channels in the cell
membrane tha seem to be at the genetic root of these phenotypes. Our data begin to
connect the dots between the growth advantage in S. paradoxus in benomyl and at low
temperatures, relative to S. cerevisiae.