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D L Nanney

Publications and source records attributed to D L Nanney.

36 records · Page 2Linked to original sources
PubMed1975

Considerations of symmetry in the cortical integration of tetrahymena doublets.

Homopolar doublets of syngen 1, T. pyriformis, may be induced by treatment of conjugating pairs with immobilizing antiserum. These doublets have geometric properties and basal body populations generally indicative of separate autonomous integrative systems in the two halves. The duplex system, though metastable, is transformed through a process of "simplification" back to the simplex state. The transformation is not a single event, but a series involving changes at different times for different structures and processes; for the micronuclei and the macronuclei; for the capacity to generate two oral apparatuses through stomatogenesis and the capacity to develop them through oral replacement; for the structures at the anterior and posterior ends of the cell; for the numbers of ciliary rows and for the numbers of basal bodies which make up the rows. Although the two semicells composing a doublet are in important respects independent of each other, they are coordinated in significant ways. The positions of the contractile vacuole pores and their numbers depend not only on the number of ciliary rows in a semicell, but also on the number of ciliary rows in the opposing twin. Most notably, the probability for dual stomatogenesis, and hence the perpetuation of the doubled oral apparatus, depends on the symmetry of the semicells. The cell as a whole is maintained as an integrated unit over a prolonged interval as various aspects of duplex structure and function are progressively consolidated.

Cilia↗
PubMed1975

Patterns of basal body addition in ciliary rows in Tetrahymena.

Most naked basal bodies visualized in protargol stains on the surface of Tetrahymena are new basal bodies which have not yet developed cilia. The rarity of short cilia is explained by the rapid development of the ciliary shaft once it begins to grow. The high frequency of naked basal bodies (about 50 percent) in log cultures indicates that the interval between assembly of the basal body and the initiation of the cilium is long, approximately a full cell cycle. Naked basal bodies are more frequent in the mid and posterior parts of the cell and two or more naked basal bodies may be associated with one ciliated basal body in these regions. Daughter cells produced at division are apparently asymmetric with respect to their endowment of new and old organelles.

Animals↗
PubMedDate not supplied

Comparison of ribosomal and isozymic phylogenies of tetrahymenine ciliates.

A recent analysis of sequence variations in ribosomal RNA's from 31 species of tetrahymenine ciliates groups them into 9 sets referred to as "ribosets." These species associations are not well correlated with the distributions of distinctive morphological characteristics. The phylogenetic structure suggests that modern "pyriform" tetrahymenines may be paraphyletic survivors of primitive design and that the morphologically distinctive forms may include examples of convergent evolution of derived forms. Alternatively, the common ancestor may have been a polymorphic species that has lost its plasticity in some derived lineages. In an attempt to test the ribosomal phylogeny, we here compare it with a phylogeny based on isozymic variation. The main features of the ribosomal and isozymic phylogenies are similar. The carnivorous (macrostome-forming) species are widely scattered in both, as are the bacteriophagous pyriform species. Isozymic and ribosomal analyses are optimally useful, however, in different contexts. Isozymic variations can distinguish species that are ribosomally identical. Ribosomal variations provide more secure evaluations of distant relationships.

Animals↗
PubMedDate not supplied

Ribosomal RNA sequencing of members of the Crypthecodinium cohnii (Dinophyceae) species complex; comparison with soluble enzyme studies.

Sixty-five members of the Crypthecodinium cohnii species complex were analyzed for sequence differences within the D2 region of the 23S ribosomal RNA molecule. On the basis of 46 sequence differences the strains fell into 19 distinct ribosets (strains of identical sequence), some with many members. Members of four of the seven major sibling species (widespread breeding groups) were each found within single ribosets. Members of three other major sibling species were each, however, divided into two ribosets by a single sequence difference correlated with geographic separation and with previously reported electrophoretic polymorphisms of soluble enzymes within the sibling species. In addition to members of major sibling species, some ribosets include many minor sibling species (each represented by only one strain). Of 38 minor sibling species, 22 shared sequence with a major sibling species. Of these 22, 14 were identical in soluble enzymes to their related major sibling species or differed by only one of three enzymes. Other minor sibling species appear to have diverged extensively from any others in both rRNA sequence and electrophoretic profile. As a group, major sibling species differ markedly in the number of minor sibling species associated with them, suggesting differences in frequency of sexually isolating events in their past histories. These findings are discussed in the context of the previously proposed model of sympatric speciation.

Animals↗
PubMedDate not supplied

Comparison of sequence differences in a variable 23S rRNA domain among sets of cryptic species of ciliated protozoa.

Studies were undertaken to discover the relative molecular distances separating some familiar forms of ciliated protozoa, and the genetic species they include. Sequences of 190 bases of the D2 domain of the large ribosomal nucleic acid molecule were obtained by polymerase chain reaction from protists of three distinctive groups of ciliated protozoa-Colpoda, Paramecium and Tetrahymena. Evolutionary trees were constructed for each set of sequences using the PHYLOGEN 1.0 string programs. All three groups of ciliates manifested large molecular diversity among strains difficult or impossible to distinguish morphologically. The largest single evolutionary distance within a group was the 75 differences separating Tetrahymena paravorax from the other tetrahymenids. The largest mean distance for a group was the 21.2 for the colpodids. In all the protist groups the large molecular diversity is obscured by morphological conservatism associated with constraints of ancient designs. The molecular diversity within morphotypes argues for long evolutionary coexistence of species differentiated from each other in significant physiological, ecological, or nutritional ways.

Animals↗