Do divergent mitochondrial backgrounds alter the fate of nuclear alleles during hybridization and admixture?

The study examines whether variations in mitochondrial DNA backgrounds impact the results of nuclear allele inheritance during hybridization and admixture. Hybridization combines genetic material from different populations or species, and selection determines the fate of individual alleles based on their fitness in the hybrid genome. As mitochondrial genes coevolve with the nuclear genome, they could be particularly susceptible to foreign nuclear backgrounds, acting as potential hotspots for hybrid incompatibilities.

To test this hypothesis, the researchers experimentally evolved three sets of five populations of hybrid Drosophila melanogaster. These populations all carried the same nuclear chromosomes but were paired with mitochondrial DNA backgrounds that varied in their degree of divergence. The team hypothesized that these accumulative incompatibilities would lead to distinct patterns of nuclear admixture depending on the mitochondrial background.

To determine this, the researchers utilized whole-genome sequencing at various intermediate time points, tracking changes in nuclear allele frequencies among the 15 populations. After a 25-generation span, the results revealed a remarkable parallel mosaic of nuclear ancestries, regardless of mitochondrial background. Contrary to their original assumption, the study found no evidence suggesting that mitochondrial background had any influence on nuclear admixture, even in interspecific combinations.

The findings suggest that in species with large effective population sizes, efficient purifying selection limits the buildup of mitonuclear incompatibilities. Consequently, nuclear allele selection can promote consistent ancestry sorting shortly after hybridization occurs.