Ciliate Mating Types and Pheromones

The story of our knowledge of ciliate mating types and their relevant signaling molecules, originally referred to as mating type substances/factors and today usually described as pheromones (to imply a more general function as chemicals used to communicate between individuals of the same species), is inextricably bound to our understanding about ciliate sexual activity. This activity is commonly manifested as conjugation, autogamy in ciliates, like parthenogenesis in animals, being an additional and much more sporadic alternative. Although conjugation has been described in a variety of organisms, ciliate conjugation is a unique phenomenon of cell-cell interaction and reversible union in mating pairs, that has nothing to do with phenomena of gamete-gamete interaction and irreversible union into a synkaryon. The two ciliates (designated as gamonts) which unite into a conjugal, or mating pair are de facto hermaphrodite, vegetatively reproducing cells which will generate two sexually complementary haploid gametic nuclei, one migratory (male) and one stationary (female), only as result of a meiotic process that involves their diploid micronuclei and is triggered by the cell mating union itself.