Since Cryptococcus, like most club fungi (Basidiomycota), must mate to produce airborne spores, researchers have been faced with a mystery. "The unusual thing about C. neoformans and C. gattii is for the vast majority of the world you can only find [one sex]," says molecular geneticist James Fraser of the University of Queensland. The trouble is that, without mating, the yeast reproduces clonally, and individual cells typically are not tiny enough to infiltrate the lungs. So how can only a single sex of Cryptococcus infect people in the open air?
There's some surprising evidence to suggest that two strains of a single sex can, in fact, mate—a process which could produce spores small enough to become airborne. A 2005 study in Nature by Joseph Heitman's group at Duke University demonstrated that a unisexual population of C. neoformans could mate to produce airborne spores in the laboratory.