Speaker
Description
The genomes of hybrids often show substantial deviations from the features of the parent genomes, including genomic instabilities characterized by chromosomal rearrangements, gains, and losses. This plastic genomic architecture generates phenotypic diversity, giving hybrids access to new ecological niches. We asked if there are any generalizable patterns and predictability in the type and prevalence of genomic variation and instability across 204 hybrid genomes with different genetic and ecological backgrounds, isolated from natural, industrial fermentation, clinical, and laboratory environments. Synchronous mapping to all eight parental species revealed significant variation in read depth indicating frequent aneuploidy, affecting 44% of all genomes. Early generation hybrids with more equal genomic content from both parents contained more aneuploidies than introgressed genomes with an older hybridization history. Interestingly, shared k-mer analysis showed that more genetically distant crosses produced more similar hybrid genomes, which may be a result of stronger negative epistasis at larger genomic divergence, putting constraints on hybridization outcomes. To illustrate the degree and potential causes of reproductive isolation between species, we analyzed hybrid spore viabilities across the entire genus, and tested for the role of genetic, geographic and ecological divergence within and between species (28 cross types, 371 independent crosses). Hybrid viability generally decreased with parental genetic distance likely due to antirecombination and negative epistasis, but notable exceptions exist, pointing to importance of strain-specific structural and ploidy variation. Surprisingly, the viability of crosses within species varied widely, from near reproductive isolation to near-perfect viability. Geographic and ecological origins of the parents predicted cross viability only to an extent. In summary, we find reliable genomic predictors of hybrid viability and genomic instability, but also report interesting cross- and environment-specific idiosyncrasies. Our results are an important step in understanding the factors shaping divergent hybrid genomes and their role in adaptive evolution.
