Paramecium bursaria: Life history. V. Some relations of external conditions, past or present, to ageing and to mortality of exconjugants, with summary of conclusions on age and death
✍ Scribed by Jennings, H. S.
- Publisher
- John Wiley and Sons
- Year
- 1945
- Tongue
- English
- Weight
- 998 KB
- Volume
- 99
- Category
- Article
- ISSN
- 0022-104X
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✦ Synopsis
Earlier communications (Jennings, '44,44a, b, c) have dealt with the periods of immaturity, maturity, and later decline ("ageing") in the life history of clones of Paramecium bursaria ; also with the relation of these periods to mortality among ex-conjugants. They have dealt further with inbreeding and its effects on ex-conjugant mortality ( '44b, c). The present contribution deals with the role of external conditions in relation to "ageing" and death of clones. It presents certain experimental data on these matters, as well a s a consideration of the data presented by other investigators. This brings to a head the problem of the prevalence and nature of ageing and death in these organisms, so that conclusions on these matters are summarized.
The following factual situation may be taken as established for Paramecium bursaria by the papers above cited:
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Clones, like individual bodies in multicellular animals, are at first sexually immature, this condition lasting, in the species named, usually for several months. The length of the period of immaturity depends in part on the conditions to which the clone is subjected, unfavorable conditions prolonging immaturity.
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The period of immaturity is followed (in many cases after a brief transitional "adolescence") by a period of sexual maturity, lasting for several years. During this period conjugation readily occurs with clones of a different sex type of the same variety.
Then follows a period of decline ("ageing") during which multiplication is slower and death of individuals becomes frequent. I n this later period death following conjugation of the old clones occurs in a high proportion of the ex-conjugants.