Study of intraclonal conjugation in Chilodonelia steini. Evidence of abortive conjugation

Mating and conjugation in the ciliate Chilodonella steini has been examined. Only intraclonal conjugation has been found thus far in this species. Stable opposite mating types have not been observed, even after extensive single cell isolations and the observation of cell lines following two consecutive generations of inbreeding. Following intraclonal conjugation, two kinds of selfing lines appear: 1) lines that enter long immaturity periods, 2) lines that do not enter immaturity at all, but maintain a permanent ability to pair. These lines do not yield immature progeny after a subsequent conjugation. Immature lines result from true conjugation as expected, whereas those lines that do not enter immaturity result from an abortive process. During normal conjugation the new macronuclear anlagen develop and the old macronucleus is resorbed. During abortive conjugation the new macronuclear anlagen also develop but the old macronucleus is not resorbed. Eventually the old macronucleus, instead of the new one, divides to provide a somatic nucleus for the progeny. Thus macronuclear retention occurs in some lines of Ch. steini similar to that observed in senescent lines of Tetrahymena thermophila.