AN APPARENT DISJUNCTION BETWEEN THE EVOLUTION OF FORM AND SUBSTANCE IN THE GENUS TETRAHYMENA.

Abstract

The highly complex cell architecture found in species of the ciliate genus Tetrahymena appears to be genus-specific, i.e., members of the 26 or so species currently recognized within this genus are essentially identical in morphology (Nanney and McCoy, 1976; Nanney, 1977; Corliss, 1973; Williams and Bakowska, 1982). On the other hand, species differences in the electrophoretic properties of soluble enzymes are considerable (Borden et al., 1973; Borden et al., 1976). The species are now defined and identified largely on the basis of isozyme patterns in conjunction with breeding tests (Nanney and McCoy, 1976). Recent studies employing 1D gel electrophoresis indicate further that the molecular dissimilarities between the species apply to surface membrane proteins (Williams et al., 1980), and to at least some structural proteins as well (Vaudaux et al., 1977; Seyfert and Willis, 1981; Buhse and Williams, 1982). This has led to the suggestion that the cell architecture is maintained by different in different species of Tetrahymena (Nanney, 1977; Vaudaux et al., 1977; Seyfert and Willis, 1981). The studies in the present investigation were undertaken to offer a rigorous test of the same morphology-different molecules hypothesis by comparing total cell and cytoskeletal protein similarities among several Tetrahymena species using both 1D and 2D polyacrylamide gel electrophoresis. Two sexual but reproductively isolated species of Tetrahymena (T. thermophila and T. americanis) were found to be different in protein arrays at a level diagnostic of mammalian genera. Two recognized asexual species (T. pyriformis and T. vorax) showed similarly large genetic distances between themselves and each of the two sexual species. Moreover, very similar estimates of genetic distance were obtained whether determined in 1D or 2D gel electrophoresis, using either cytoskeletal or total cell proteins. The which make up the unique cellular architecture found in species of the genus Tetrahymena appear to have undergone extensive evolutionary divergence, even though the specific architecture itself has been highly conserved within the genus.