A Genetic Screen for Vegetative Gene Expression in the Micronucleus of Tetrahymena thermophila

ABSTRACT. The presence of a micronucleus with at least a small portion of the micronuclear genome appears to be indispensable for vegetative viability in the ciliate Tetrahymena thermophila . A genetic screen was devised to detect evidence of expression of essential genes in the vegetative micronucleus by identification of thermosensitive-lethal mutations expressed in the absence of nuclear reorganization. Although control experiments demonstrated the efficacy of the method for induction and recovery of thermosensitive lethal mutations in micronuclear genes, no expressed mutations were recovered in the absence of nuclear reorganization. This finding complements the existing lack of convincing biochemical evidence for gene expression in the vegetative micronucleus and suggests that the essential function may involve genomic DNA sequences for which thermosensitive mutant alleles are not recoverable, or perhaps a non-genomic component of the organelle.     

Phylogenetic position of the trichomonad parasite of turkeys, Histomonas meleagridis (Smith) Tyzzer, inferred from small subunit rRNA sequence.

The phylogenetic position of the trichomonad, Histomonas meleagridis was determined by analysis of small subunit rRNAs. Molecular trees including all identified parabasalid sequences available in data bases were inferred by distance, parsimony, and likelihood methods. All reveal a close relationship between H. meleagridis, and Dientamoeba fragilis. Moreover, small subunit rRNAs of both amoeboid species have a reduced G + C content and increased chain length relative to other parabasalids. Finally, the rRNA genes from H. meleagridis and D. fragilis share a recent common ancestor with Tritrichomonasfoetus, which exhibits a more developed cytoskeleton. This indicates that Histomonas and Dientamoeba secondarily lost most of the typical trichomonad cytoskeletal structures and hence, do not represent primitive morphologies. A global phylogeny of parabasalids revealed significant discrepancies with morphology-based classifications, such as the polyphyly of most of the parabasalid families and classes included in our study.     

An uncommon oyster breeding system in a Late Tertiary Patagonian species

Iribarne, O. O., Pascual, M. S. & Zampatti, E. A. 1990 04 15: An uncommon oyster breeding system in a Late Tertiary Patagonian species. Lethaia , Vol. 23 , pp. 153–156. Oslo. ISSN 0024–1164.
The brooding extant species Ostrea puelchana has a breeding system that is unique among living oysters. Females larger than 55 mm often carry small epidictic males (up to 30 mm) on the anterior edge of the concave shell. These are strongly attached when small, but become relatively less strongly attached as they grow larger. Field experiments show that their growth is retarded as a result of the influence of the carrier. Advantages of this mating system are reflected in the success of fertilization; sperm transfer is facilitated safely during long periods of the oyster's life. A similar attachment pattern was found in a fossil oyster, Ostrea aluarezi , from a Patagonian deppsit. The finding suggests that this particular reproductive strategy had already evolved among late Tertiary ostreids. * Epibiotic. breeding system, fossil , Ostrea alvarezi, oyster, Tertiary .     

Protein Polymorphism and Evolution in the Genus Tetrahymena1

ABSTRACT. Immunoblotting tests involving cytoskeletal protein arrays and fluorescence microscopical examinations of whole cells using monoclonal antibody 424A8 gave substantially different results in three evolutionary subgroups within the genus Tetrahymena. These responses are described and some implications of the evolutionary divergence indicated in this ciliated protozoan are discussed.     

Isospora spilogales n. sp. and I. sengeri n. sp. (Protozoa: Eimeriidae) from the Spotted Skunk, Spilogale putorius ambarvalis

SYNOPSIS. Two new species of Isospora are described from the feces of an eastern spotted skunk Spilogale putorius ambarvalis imported into Montana from Florida. The oocysts of I. spilogales n. sp. are 29 to 38 by 22 to 28 μ and contain 2 sporocysts measuring 17 to 22 by 13 to 16 μ; a few Caryospora -like oocysts containing a single sporocyst were considered abnormal I. spilogales oocysts. The oocysts of I. sengeri n. sp. are 16 to 23 by 12 to 18 μ and contain 2 sporocysts measuring 10 to 14 by 8 to 12 μ.     

Female‐biased size dimorphism in a diapausing caddisfly,Mesophylax aspersus: effect of fecundity and natural and sexual selection

1. The effect of mating success, female fecundity and survival probability associated with intra‐sex variation in body size was studied in Mesophylax aspersus, a caddisfly species with female‐biased sexual size dimorphism, which inhabits temporary streams and aestivates in caves. Adults of this species do not feed and females have to mature eggs during aestivation. 2. Thus, females of larger size should have a fitness advantage because they can harbour more energy reserves that could influence fecundity and probability of survival until reproduction. In contrast, males of smaller size might have competitive advantages over others in mating success. 3. These hypotheses were tested by comparing the sex ratio and body size of individuals captured before and after the aestivation period. The associations between body size and female fecundity, and between mating success and body size of males, were explored under laboratory conditions. 4. During the aestivation period, the sex ratio changed from 1 : 1 to male biased (4 : 1), and a directional selection on body size was detected for females but not for males. Moreover, larger clutches were laid by females of larger size. Finally, differences in mating success between small and large males were not detected. These results suggest that natural selection (i.e. the differential mortality of females associated with body size) together with possible fecundity advantages, are important factors responsible of the sexual size dimorphism of M. aspersus. 5. These results highlight the importance of taking into account mechanisms other than those traditionally used to explain sexual dimorphism. Natural selection acting on sources of variation, such as survival, may be as important as fecundity and sexual selection in driving the evolution of sexual size dimorphism.     

Developmental Life Cycle of Leishmania—Cultivation and Characterization of Cultured Extracellular Amastigotes1

ABSTRACT. The biochemistry and immunology of Leishmania promastigotes has been extensively studied; this is due primarily to the facility with which this stage, in contrast to the amastigotes stage, can be maintained in axenic culture. Several attempts to axenically culture lines of Leishmania amastigotes have been reported in the literature. This paper summarizes methods of adaptation (low pH, elevated temperature and culture medium) and characterization of several axenic lines of Leishmania amastigotes. Based on morphological, biological, immunological and biochemical evidence, these organisms appear to resemble amastigotes from infected macrophages or tissue. The axenically cultured amastigotes appear to be distinct from shocked (heat, serum deprivation, stressed) Leishmania promastigotes in the plethora of proteins synthesized, growth (multiplication) in culture, and developmental regulation observed. These data suggest that Leishmania organisms have a significant developmental response to certain signals (pH, temperature) mimicking their in vivo macrophage milieu. The response to other environmental parameters characteristic of the host-macrophage remain to be determined. These axenically cultured amastigotes should be of interest for further immunological, biochemical and developmental investigations of the disease-maintaining stage of this parasite.     

Methionine or Folate and Phosphoenolpyruvate in the Biosynthesis of Threonine in Crithidia fasciculata1

SYNOPSIS. Crithidia fasciculata can synthesize threonine but it lacks an aspartokinase. The carbons of threonine may be derived from methionine when it is present in the medium. However, methionine can be synthesized by the organism provided organic sulfur is present. When both methionine and threonine are omitted from the medium, growth will occur if cysteine and high levels of folate are present. The compound common to both methionine and threonine under these conditions, α-keto-γ-hydroxy-butyrate, is derived from phosphoenolpyruvate (PEP) and the β-carbon of serine. High levels of folate are required for this coupling reaction, which is carried out by what may be called phosphoenolpyruvate-tetrahydrofolate hydroxymethyltransferase. By the use of radioactive tracers, both in growth experiments and in cell-free preparations, virtually all of the intermediates in these two series of reactions were identified.