The macronucleus of Paramecium divides amitotically, and daughter macronuclei with different DNA contents are frequently produced. If no regulatory mechanism were present, the variance of macronuclear DNA content would increase continuously. Analysis of variance within cell lines shows that macronuclear DNA content is regulated so that a constant variance is maintained from one cell generation ...

A simple method for indoor and outdoor cultivation of Mesocyclops aspericornis, Macrocyclops albidus and Mesocyclops n. sp. copepods is presented. This method utilizes Chilomonas sp., Paramecium caudatum and fresh lettuce as food sources for copepod cultures. Steps for initiating and maintaining copepod cultures are provided.

A single cell of the green paramecia (Paramecium bursaria) harbors several hundreds of endo-symbiotic Chlorella-like algae in its cytoplasm. Removal of algae from the host organism and re-association of ex-symbiotic host paramecia with ex-symbiotic algae can be experimentally demonstrated in the laboratory. However, the mechanism precisely governing the alga-protozoan association is not fully u...

N Paramecium aurelia a number of factors interact to determine the I occurrence of conjugation. Most attention has in the past been given to the role of environmental conditions. In this paper an internal factor is dealt with: nuclear reorganization of the type occurring both a t endomixis and a t conjugation. As will be shown, the relation of these nuclear processes to the subsequent occurrenc...

Dispersal can have positive and negative effects on metapopulation stability and persistence. One prediction is that high levels of dispersal synchronize density fluctuations between subpopulations. However, little is still known about how biotic and abiotic factors combine to modify the effects of dispersal rate on synchrony and metapopulation dynamics. In a fully factorial experimental design...

HE killer trait in all stocks of Paramecium aurelia which have been investiTgated has been found to depend upon the presence of a cytoplasmic factor, kappa, carried by killers but absent from sensitive animals (SONNEBORN 1943). Kappa is a DNA containing particle of about one micron in size (PREER 1950a; PREER and STARK 1953). When kappa disappears from the cytoplasm of a killer, the animal lose...

The surprising discovery of a whole-genome duplication in the otherwise compact genome of Paramecium tetraurelia displays the early forces driving gene retention and loss.

Piwi proteins and piRNAs protect eukaryotic germlines against the spread of transposons. During development in the ciliate Paramecium, two Piwi-dependent sRNA classes are involved in the elimination of transposons and transposon-derived DNA: scan RNAs (scnRNAs), associated with Ptiwi01 and Ptiwi09, and iesRNAs, whose binding partners we now identify as Ptiwi10 and Ptiwi11. scnRNAs derive from t...

Cells of Paramecium caudatum, syngen 3 usually become sexually mature about 50 fissions after conjugation. In order to study the genetic mechanisms that control fission-department expression of maturity, an attempt was made to obtain early mature mutants by treatment with N-methyl-N'-nitro-N-nitrosoguanidine. A new cytoplasmic marker, erythromycin resistance, was used to eliminate nonconjugant ...