Genetic dissection of an ancient divergence in yeast thermotolerance

Some of the most unique and compelling survival strategies in the natural world are fixed in isolated species. To date, molecular insight into these ancient adaptations has been limited, as classic experimental genetics has focused on interfertile individuals in populations. Here we use a new mapping approach, which screens mutants in a sterile interspecific hybrid, to identify eight housekeeping genes that underlie the growth advantage ofSaccharomyces cerevisiaeover its distant relativeS. paradoxusat high temperature. Pro-thermotolerance alleles at these mapped loci were required for the adaptive trait inS. cerevisiaeand sufficient for its partial reconstruction inS. paradoxus. The emerging picture is one in whichS. cerevisiaeimproved the heat resistance of multiple components of the fundamental growth machinery in response to selective pressure. This study lays the groundwork for the mapping of genotype to phenotype in clades of sister species across Eukarya.