Speaker
Description
Hybridization has shaped the evolutionary history of every kingdom of life. Hybridization inherently forces genomes that are not optimized to function together into the same cell. Remarkably, despite in some cases extreme sequence divergence upwards of 30%, cells can survive this challenge and even exploit it to rapidly evolve to new environments and create novelty. However, much of what we know of hybrids derives from extant hybrids, thus how populations resolve the challenges of hybridization and the genome dynamics of this process are still not fully understood. Taking advantage of Saccharomyces yeast as a model we generated hybrids ranging from 0.5 to approximately 40% parental sequence divergence. We used two approaches to do so, one being a single-cell mating approach which reduces competition and selection and has the advantage of allowing for lineage tracking, the other being a standard mass mating approach which is characterized by high selection, to generate all crosses. We found, using a heat shock protein reporter, that hybridization initially creates an acute stress response that is later attenuated. We subjected our panel of hybrids to genome sequencing and found that hybrids across a range of sequence divergences rapidly fixed aneuploidies and loss of heterozygosity. Interestingly, genome instability was not restricted to nuclear genomes but extrachromosomal sequences and mitochondrial genomes both exhibited copy number variations across hybrid lineages. Through both Hi-C and genome sequencing we strikingly observed convergent evolution around spontaneous polyploidization events in various hybrid lineages across a range of sequence divergences of parental founders when natural selection was minimized and maximized. A number of these polyploidization events perfectly recapitulated polyploidization events that have been identified by similar extant hybrids in the wild. Ongoing investigation is being conducted to track the timing, the frequency, the level of convergence across lineages, and the persistence of these genomic changes over evolutionary time in various environments. Thus far, our results provide unique empirical insights into the evolutionary dynamics and impacts of hybridization and identify a multitude of genomic responses and when they arise in hybrid evolutionary trajectories.
