Introgression maintains the genetic integrity of the sex-determining chromosome of the fungus Neurospora tetrasperma

Genome evolution is driven by a complex interplay of factors, including selection, recombination, and introgression. The regions determining sexual identity are particularly dynamic parts of eukaryotic genomes that are prone to molecular degeneration associated with suppressed recombination. In the fungus Neurospora tetrasperma, it has been proposed that this molecular degeneration is counteracted by the introgression of non-degenerated DNA from closely related species. In this study, we used comparative and population genomic analyses of variation among 92 genomes from eight phylogenetically and reproductively isolated lineages of N. tetrasperma, and its three closest relatives, to investigate the factors shaping the evolutionary history of the genomes. We found that suppressed recombination extends across at least 6 Mbp (~63%) of the mating-type (mat) chromosome in N. tetrasperma, and is associated with decreased genetic diversity, which is likely the result primarily of selection at ...