title: Loss of Heterozygosity Drives Adaptation in Hybrid Yeast.
abstract: Hybridization is often considered maladaptive, but sometimes hybrids can invade new ecological niches and adapt to novel or stressful environments better than their parents. The genomic changes that occur following hybridization that facilitate genome resolution and/or adaptation are not well understood. Here, we examine hybrid genome evolution using experimental evolution of de novo interspecific hybrid yeast Saccharomyces cerevisiae × Saccharomyces uvarum and their parentals. We evolved these strains in nutrient-limited conditions for hundreds of generations and sequenced the resulting cultures identifying numerous point mutations, copy number changes, and loss of heterozygosity (LOH) events, including species-biased amplification of nutrient transporters. We focused on a particularly interesting example, in which we saw repeated LOH at the high-affinity phosphate transporter gene PHO84 in both intra- and interspecific hybrids. Using allele replacement methods, we tested the fitness of different alleles in hybrid and S. cerevisiae strain backgrounds and found that the LOH is indeed the result of selection on one allele over the other in both S. cerevisiae and the hybrids. This is an example where hybrid genome resolution is driven by positive selection on existing heterozygosity and demonstrates that even infrequent outcrossing may have lasting impacts on adaptation.
authors.affiliation: Department of Genome Sciences, University of Washington, Seattle, WA.
authors.forename: Caiti S
authors.initials: CS
authors.lastname: Smukowski Heil
authors.affiliation: Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ.
authors.forename: Christopher G
authors.initials: CG
authors.lastname: DeSevo
authors.affiliation: Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ.
authors.forename: Dave A
authors.initials: DA
authors.lastname: Pai
authors.affiliation: Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ.
authors.forename: Cheryl M
authors.initials: CM
authors.lastname: Tucker
authors.affiliation: Department of Embryology, Howard Hughes Medical Institute, Carnegie Institution, Baltimore, MD.|Department of Biology, Johns Hopkins University, Baltimore, MD.
authors.forename: Margaret L
authors.initials: ML
authors.lastname: Hoang
authors.affiliation: Department of Genome Sciences, University of Washington, Seattle, WA.
authors.forename: Maitreya J
authors.initials: MJ
authors.lastname: Dunham
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics*; D005075:Biological Evolution; D016678:Genome / Q000235:genetics; D006824:Hybridization, Genetic / Q000235:genetics; D019656:Loss of Heterozygosity / Q000235:genetics*; D012440:Saccharomyces / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics
keywords: Saccharomyces cerevisiae; Saccharomyces uvarum; adaptation; experimental evolution; hybrid; loss of heterozygosity