The evolution of Antarctic yeasts: DNA base composition and DNA–DNA homology

The 16 biotypes of the Cryptococcus vishniacii complex of anamorphic yeasts (Basidioblastomycetes), unique to the Dry Valleys of Antarctica, include seven species separated by DNA–DNA homologies of less than 52%. Since species belonging to the complex can be as distantly related as C. bhutanensis (a Himalayan yeast, guanine + cytosine (G + C) 54.18 mol%) is to these species, a common ancestor probably originated and speciated outside of the Dry Valleys. The species C. vishniacii (G + C 54.52–55.48 mol%) comprises seven varieties with greater than 59% DNA–DNA homology and must therefore have been established in the Dry Valleys long enough to have evolved these divergent genomes. In the C. vishniacii complex, G + C values differing by more than 1 mol% are accompanied by DNA–DNA homologies of less than 23%.