Heterosis in yeast hybrids
We are particularly interested in the performance of the first hybrid generation (F1 hybrids), especially when hybrids are viable and able to outperform one or both parents under different environmental conditions, a phenomenon known as heterosis. The aim of our work was to understand mechanisms underlying heterosis, thus we used Saccharomyces yeasts as a model system due to their laboratory practicality, ability to form viable hybrids and reliable fitness measurements. First, we competed a range of different F1 hybrids with wild or domesticated background; we identified prevalent heterosis for crosses between domesticated and wild populations of different yeast species but not for crosses between wild populations of the same yeast species. By using monosporic clones as parental strains in heterosis studies we might be inflating heterosis measurements due to parental disadvantage and not the F1 hybrid advantage. Thus we set out to compared asexual fitness of heterozygous yeast isolates with homozygous monosporic clones for both domesticated and wild yeast populations; we found that domesticated monosporic clones have a significant decrease in fitness, which can potentially account for the difference in heterosis of D1 hybrids with a domesticated or a wild background. Finally we analysed the transcription of a representative heterotic F1 hybrid in comparison to its parents. Hybrid transcription was dynamic, resembling the fitter parent for the environments tested. For the first time to our knowledge, specific transcription at a multigenic level was identified has a source of heterosis, which render the F1 hybrid better adapted than its parents to variable environmental conditions. Heterosis studies in Saccharomyces yeasts, due to their simplicity, can evidence characteristics with an impact on heterosis while also tracing the evolutionary history of divergent populations.