Ploidy instability in experimental hybrid populations. Saccharomyces

Hybrids between species frequently suffer from reduced fertility. Following the propagation of 672 yeast lines through 770 mitotic generations in which natural selection was minimized, we show that inter-species diploid hybrids can recover fertility spontaneously and rapidly to the level of parental lineages through whole-genome duplication. Although rare, these events occurred in hybrids between incipient species as well as between well-established species. Our results show that the instability of hybrid ploidy is a powerful mechanism to overcome species barriers.