High-frequency switching in Dictyostelium.

A high-frequency switching system is demonstrated to exist in Dictyostelium discoideum. Switch phenotypes are distinguished by colony morphology and include changes in developmental timing as well as blocks in morphogenesis. The switching system exhibits the following characteristics: (1) a "low" spontaneous frequency of switching (approximately 10(-2] in the parent strain; (2) stimulation of the basal level of switching roughly fivefold with low doses of ultraviolet light; (3) "high" spontaneous frequencies of switching (as high as 10(-1] in particular variant strains; (4) high spontaneous frequencies of interconvertibility between variant phenotypes; (5) high spontaneous frequencies of reversion to the wild-type phenotype; (6) a set of reproducible switch phenotypes; (7) heritability of switch phenotypes; and (8) a rough correlation between switch phenotype and switching frequency. The extraordinary similarity between the switching systems in D. discoideum and Candida albicans is discussed.