Introgression, a Major Contributor to Fungal Genetic Variation found by Population Genomics.

Population genomic studies of populations of both Coccidioides species and Neurospora crassa have revealed significant introgression. With Coccidioides, as much as 7% of the genome of C. immis can be traced to its sister species, C. posadasii [Neafsey et al. 2010]. One of the introgressed regions has the hallmarks of a selective sweep indicating that at least one of the genes in the region could be important to adaptation [Whiston et al. 2012]. Population genomics of N. crassa found two, recently diverged populations each with two more recently introgressed regions. Gene deletion studies identified two genes that contribute to fitness of the northern population when growing at annual low temperatures [Ellison et al. 2011].  Although these are just two studies, the implication is that hybridization and introgression are important mechanisms that promote genetic diversity in natural populations of fungi.












Figure 1. Sliding-window analysis of species divergence (Fst) on the largest chromosome of Coccidioides species. High Fst values indicate strong local divergence between C. immitis and C. posadasii. Introgression is indicated where Fst values approach zero (*), that is, where there is no divergence between the regions of both species [Neafsey et al. 2010].