Altered Flagellar Size-Control in shf-1 Short-Flagella Mutants of Chlamydomonas reinhardtii

Two allelic Mendelian mutations which confer a short flagella phenotype were used to explore flagellar size control in Chlamydomonas reinhardtii. When mutant/wild type quadriflagellate dikaryon cells were constructed, their two short flagella rapidly grew out to near wild type length. The kinetics of elongation suggest that the flagellar assembly process is not intrinsically self-limiting as a number of otherwise attractive models for size control require. Instead, we suggest that there exists a cellular machinery dedicated to flagellar size control and that the short-flagella mutations alter the machinery in some as yet unknown way. One of the mutants shows temperature-sensitive flagellar assembly, and both are flagellaless in acetate media. Genetic analysis indicates that the temperaturesensitive, acetate-sensitive, and short-flagella phenotypes have a common genetic basis. The responsible gene has been named shf-1, and it has been mapped to chromosome VI, approximately 5 map units from the centromere.     

Ultrastructure of the Amoeboflagellate Tetramitus rostratus1

The life-cycle of the amoeboflagellate Tetramitus rostratus includes amoeboid, cyst, and flagellate stages. The ultrastructure of these three stages is illustrated, with particular emphasis on flagellate morphology. Amoeba morphology is typical of that of limax amoebas. Cysts, forming from trophic amoebas, are enclosed by a wall made up of two layers: ectocyst (ca. 70 nm), and endocyst (200 nm). The wall apparently forms from precursor material present in vesicles in the pre-cyst stage cytoplasm. Flagellate morphology is characterized by a well-defined top-shaped profile, maintained by microtubules under the plasma membrane. The flagellar apparatus or mastigont consists of four flagella, their basal bodies, sheaves of microtubules associated with two of the basal bodies, and several rhizoplasts (periodicity 20 nm). A deep, microtubule-supported, ventral invagination appears to function as a gullet. A small number of mitotic stages observed in amoeboid and flagellate individuals suggests similarity in the division process in both stages: intranuclear mitotic apparatus, nucleolus persisting through mitosis, no centrioles or basal bodies functioning as centrioles, difficulty in resolving chromosomes. The text compares ultrastructures of several amoeboflagellate organisms and evaluates the phylogenetic significance of those features common to different species. On the basis of this study, Tetramitus most closely resembles Naegleria spp.     

Land-use change and the carbon cycle

Changes in land use between 1850 and 1980 are estimated to have increased the global areas in croplands, pastures, and shifting cultivation by 891, 1308, and 30 × 10⁶ ha, respectively, reducing the area of forests by about 600 × 10⁶ ha, releasing about 100 PgC to the atmosphere, and transferring about 23 PgC from live vegetation to dead plant material and wood products. Another 1069 × 10⁶ ha are estimated to have been logged during this period, and the net release of carbon from the combined processes of logging and regrowth contributed 23 PgC to the 100-PgC release. Annual rates of land-use change and associated emissions of carbon have decreased over the last several decades in temperate and boreal zones and have increased in the tropics. The average release of carbon from global changes in land use over the decade of the 1980s Is estimated to have been 1.6 ± 0.7 PgC y^?1 almost entirely from the tropics. This estimate of carbon flux is higher than estimates reported in recent summaries because it is limited here to studies concerned only with changes in land use. Other recent analyses, based on data from forest inventories, have reported net accumulations of carbon as high as 1.1 PgC y^?1 in temperate and boreal zones. Because the accumulation of carbon in forests may result from natural processes unrelated to land-use change, estimates based on these inventories should be distinguished from estimates based on changes in land use. Both approaches identify terrestrial sinks of carbon. The argument is made here, however, that differences between the two approaches may help identify the location and magnitude of heretofore ‘missing’ sinks. Before different estimates can be used in this way, analyses must consider similar geographical regions and dates, and they must account for the accumulation and loss of carbon in forest products in a consistent fashion.     

How a Kantian Can Accept Evolutionary Metaethics

Contrary to widely held assumptions, an evolutionary metaethics need not be non-cognitivist. I define evolutionary metaethics as the claim that certain phenotypic traits expressing certain genes are both necessary and sufficient for explanation of all other phenotypic traits we consider morally significant. A review of the influential cognitivist Immanuel Kants metaethics shows that much of his ethical theory is independent of the anti-naturalist metaphysics of transcendental idealism which itself is incompatible with evolutionary metaethics. By matching those independent aspects to an evolutionary metaethics a cognitivist Kantian evolutionary metaethical theory is a possibility for researchers to consider.     

A Redescription of Uronema nigricans*

SYNOPSIS. Uronema nigricans, a hymenostome ciliate, is redescribed by modern technics. Anatomic studies were made on 4 strains treated primarily with the Chatton-Lwoff silver impregnation technic. Particular attention was given to the buccal apparatus and its importance to generic assignment in the order Hymenostomatida.     

Platyamoeba stenopodia. n. g., n. sp., a Freshwater Amoeba*

SYNOPSIS. Platyamoeba stenopodia n. g., n. sp., isolated from a lake in Alabama, is an amoeba with flattened form, usually more than 2.5 × as long as broad, the anterior half hyaline and the posterior half granular, with a single vesiculate nucleus at the posterior edge of the hyaline region. It forms a transitory floating stage with slender, hyaline pseudopods. Its cyst is spherical, uninucleate, with a smooth inner wall and a thinner, closely applied outer wall, which is often slightly wrinkled. Length of locomotive amoeba 15–36 μ diameter of cyst 7–11.5 μ Reproduction by binary fission with mesomitotic nuclear division, the nuclear membrane disappearing in prophase. The genus Platyamoeba is erected for amoebae including this organism; the type species is P. placida.     

A novel method for collection and preservation of faeces for genetic studies

Quantitative and qualitative measurements of DNA were used to compare faecal sample storage in ethanol and silica with a novel method (two‐step) in which samples are soaked in ethanol and then desiccated with silica. Silica‐preserved samples had the lowest DNA concentrations. The two‐step method yielded significantly more DNA in high quality samples (average DNA concentrations > 100 pg/µL with all storage methods). However, for lower quality samples, the ethanol and two‐step methods performed similarly. The amounts and rates of sample degradation were not strongly affected by storage method and neither was the percentage of target DNA (< 1%) obtained from the samples.