ABSTRACT
It was investigated whether the closely related species Stylonychia lemnae and Stylonychia mytilus occur in North America. Eigthy-one Stylonychia cells were collected in the surroundings of Ithaca, N.Y., USA. A comparison of their isoenzyme patterns and the number of dorsal cilia with those of Eurasian clones demonstrated that 79 clones belong to S. lemnae and 2 to S. mytilus. The mean genetic identity between the European and the North American populations of S. lemnae is 84% which is characteristic for different populations of one species. Only 33 of the North American clones conjugated. F 1 and F 2 exconjugants (North American × European clones) are as viable as exconjugants from European clones. Crossings of North American × European clones with different isoenzyme alleles demonstrated that the genetic material is exchanged. In contrast, many of the other 46 nonconjugating North American clones can start but do not finish conjugation ("pseudoconjugation" without genetic exchange). Some of these clones have Mi without function, small Mi or no Mi at all. Some clones also show a peculiar DNA banding pattern with several highly overamplified DNA sequences. It is concluded that the American populations of S. lemnae contain clones which diverge in several characteristics from the European/Asian clones.
ABSTRACT
Macronuclear DNA of four hypotrichous and one holotrichous ciliate species was characterized by biochemical techniques. The renaturation kinetics of the macronuclear DNAs of all five species were similar. Repetitive sequences occur only in an amount below 2%. Although the DNA content of the macronuclei of the species differs considerably, the kinetic complexity of the macronuclear DNA is rather uniform (around 3 x 10(10) daltons, i.e., 4-11 x the E. coli genome). Only in the macronuclei of the hypotrichous species the DNA exists as gene-sized fragments.
