Little is known about the frequency and outcome of genetic recombination in natural populations of single-celled organisms. In one group of single-celled organisms, the ciliated protists, genetic recombination occurs by means of conjugation. Unlike genetic recombination in plants and animals, conjugation is disconnected from reproduction, which occurs by simple binary fission. Conjugation is a rejuvenating event that initiates a new life cycle. This research combines field and laboratory studies of conjugation and multiple mating types in the ciliate Tetrahymena thermophila. This species, which has seven mating types, is widely used in molecular biology but its ecology is poorly known. We will test two hypotheses: first, that conjugation occurs frequently in natural populations, and second, that the frequencies of the mating types are determined by both genotype and by the temperature of the environment. The results will provide increased understanding of an ecologically important group of protists, and will be relevant to the ongoing debate over the origin and implications of sexual reproduction and genetic recombination.//
