Title: Introgression and genome evolution: insights from the model Neurospora

Abstract:

Genome evolution is driven by a complex interplay of multiple factors, including selection, recombination, and introgression. The regions determining sexual identity are particularly dynamic parts of eukaryotic genomes that are prone to molecular degradation associated with suppressed recombination. In the fungus Neurospora tetrasperma, suppressed recombination extends across at least 6 Mbp (~63%) of the mating-type (mat) chromosome, and we have in numerous studies confirmed that it is associated with the accumulation of non-beneficial mutations. Recent data from our lab suggest that this molecular degradation is counteracted by the introgression of non-degraded DNA from closely related species. By using comparative and population genomic analyses we found that suppressed recombination is associated with decreased genetic diversity, which is likely the result primarily of selection at linked sites. Furthermore, the mat chromosomes appears to be temporarily regenerated via introgression from sister species; six out of eight lineages show introgression into one of their mat chromosomes, with at least three other Neurospora species acting as donors. The introgressed tracts have been driven to fixation in lineages, suggesting that they confer an adaptive advantage in natural populations, and our analyses support the presence of selective sweeps in at least one of the lineages. Thus, these data strongly support a hypothesized role of introgression as a mechanism for the maintenance of mating-type determining chromosomal regions, and highlight the importance of introgression for eukaryote genome evolution.