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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

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Kosaka Toshikazu; Predominance of Autogamy over Conjugation in a New Syngen in Fresh-water Euplotes woodruffi (Ciliophora). J.Sci.Hiroshima Univ.,Ser.B,Div.1 30:111-122, 1982

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Syngen 2 which is endowed with the ability to undergo autogamy and conjugation was found from a fresh-water river in Euplotes woodruffi. How both the processes are mutually related is examined in this study. Four stocks which were examined can undergo autogamy. Exautogamonts produce viable clones at a ratio of 65 to 80%. These clones always have an immature period for autogamy, during which an average of 62.9 cell divisions occurs in stock HR-2, 64.1 in HR-3, 43.3 in HR-5, and 95.8 in HR-8. The frequency of cells which can take part in autogamy increases gradually with advance of clone age. In an exautogamous clone from HR-5, for example, the frequency is 1.4% at the 36th fission, 79% at the 59th, and reaches to 100% at the 77th. There are 3 mating types in syngen 2; three stocks (HR-2, HR-3, HR-5) can mate with one another; the other (HR-8) conjugates only with HR-2. The conjugating pairs are always formed when two parental stocks which are in autogamy maturity are mixed together under a suitable condition for inducing autogamy. Under other conditions conjugation is never induced. Cells of the mixture contribute to conjugation in less than 1% and to autogamy in more than 70%. Viability of the exconjugants is 8 to 17% in 3 crosses (HR-2xHR-3, HR-3xHR-5, HR-2xHR-8) and 55% in one cross (HR-2xHR-5). However, all the viable exconjugant clones obtained are doomed to die within 48 cell divisions after establishment. Exconjugant clones (F1) have no autogamy immaturity, so that they can undergo autogamy immediately after clone initiation. This autogamy usually is abortive but sometimes it can produce progeny clones (F2) doomed to death. The doomed exautogamous clones are produced in this way in F3 to F4 generations, but they undergo abortive autogamy without passing through autogamy immaturity. The final autogamy in each clone is completely mortal. For example, in isolated lines which have been derived from exconjugant clones of cross HR-2xHR-3, the exautogamonts are viable in 0-15% in F2 generation, 0-10% in F3, and 0% in F4. It is thus evident that syngen 2 retains a predominance of autogamy over conjugation. Syngen 2 is discussed with the other two groups from the standpoint of species problem.