Sex in Protists

By Linda Hufnagel, University of Rhode Island

Illustrated Guide II Protistan sexual activities are as diverse as the protists themselves. Providing an opportunity for genetic recombination, protistan mating interactions may involve gametes (+ and -, male and female, type a and type a, macrogametes and microgametes, etc) or mating types (which can vary from two, like humans, to many! How confusing that must be!!). Sexual reproduction is a misnomer, because reproduction of the participants does not take place until after the important events have occurred. The significant events of sexual processes in protists are meiosis, to produce haploid genomes, and fusion of gametes (as in Chlamydomonas or Plasmodium) or gametic nuclei (as in the ciliates Tetrahymena and Paramecium), to bring about new combinations of genetic information. In many protists, a sexual cycle has not been found, but that could be because the shy creatures do not wish to be observed in the act! All kidding aside, in these so-called non-sexual species the conditions required for the cells to become mating competent may not yet have been identified.

Scientists are researching many interesting aspects of mating in protists, including the production and properties of mating signals (pheromones) and their receptors, secretion of mating specific agglutinins and morphogenetic changes in the participating cells. Particularly exciting and unique is the process of macronuclear development in mating cilioprotists, during which a new, polygenic macronucleus is formed from a diploid micronucleus recently formed by fusion of haploid nuclei. The old macronucleus undergoes apoptosis, but not before it leaves its mark on a new mac, leading to the non-mendelian inheritance of phenotypic properties.

Here is a small selection of web sites with images and information about mating in protists:, a biotech company Ambion discusses gene sequence elimination during MIC to MAC conversion in the ciliate, Tetrahymena., basic events of conjugation in Tetrahymena., Images of mating Paramecium., Mating in Tetrahymena is described, with accompanying fluorescent images., Methods are described, for DNA-mediated transformation in Tetrahymena, with accompanying diagrams., Inheritance in ciliates is summarized; from Developmental Biology, by Scott Gilbert., the web site of Martin Gorovsky, with information on his research on mating in Tetrahymena., Research on mating in Chlamydomonas, from the laboratory of Ursula Goodenough., Chlamydomonas mating research from the laboratory of William Snell., Information on mating in Chlamydomonas., Agglutination mutant affecting mating in Chlamydomonas., a method for looking at the transmission or organellar genes during mating in Chlamydomonas., a student report on Chamydomonas, by Alexander Cuenca, from the University of Miami., An introduction to mating in Chlamydomonas., mating in the yeast, Candida albicans., mating types in yeast., about yeast mating type switching., a yeast mating movie., sex in slime molds