Evolution of MAT in the Candida Species Complex: Sex, Ploidy, and Complete Sexual Cycles in C. lusitaniae, C. guilliermondii, and C. krusei
The best-studied species to date are the human pathogens Candida albicans and C. glabrata. However, neither of these species is as yet known to possess a complete meiotic sexual cycle. C. lusitaniae, C. guilliermondii, and C. krusei are three members of this genus that are exciting prospects for further study. Of the three species discussed in this chapter, the sexual life cycle has been the best studied for this species. Multiple types of media are capable of inducing mating including dilute potato dextrose agar, 1% malt extract media, sodium acetate, yeast carbon base, V8, and SLAD. The anamorph has been cultured from a variety of ecological niches, including human clinical specimens, insects, fruit, and decaying matter. The sexual cycle of C. guilliermondii was first identified in 1952 by Wickerham and Burton, after recognizing that some yeasts previously classified to non-ascosporeforming genera actually represented the anamorphic form of a sexual species. That sexual Candida species exist forms the basis of the argument that loss or restriction of sexual reproduction is the evolved state, possibly due to the energy expenditure required to undergo meiosis or to limit genetic exchange in a pathogen highly evolved to its host niche. Thus, continued study of the Candida species complex will provide insight on interesting evolutionary questions regarding the evolution of signal transduction pathways, sexual reproduction, commensalism, and pathogenesis.
