Explaining geographical variation in the isotope composition of mouse lemurs (Microcebus)

Aim We sought to quantify geographical variation in the stable isotope values of mouse lemurs (Microcebus) and to determine whether this variation reflects trophic differences among populations or baseline isotopic differences among habitats. If the latter pattern is demonstrated, then Microcebus can become a proxy for tracking baseline habitat isotopic variability. Establishing such a baseline is crucial for identifying niche partitioning in modern and ancient communities. Location We studied five species of Microcebus from eight distinct habitats across Madagascar. Methods We compared isotopic variation in C₃ plants and Microcebus fur within and among localities. We predicted that carbon and nitrogen isotope values of Microcebus should: (1) vary as a function of abiotic variables such as rainfall and temperature, and (2) covary with isotopic values in plants. We checked for trophic differences among Microcebus populations by comparing the average difference between mouse lemur and plant isotope values for each locality. We then used multiple regression models to explain spatial isotope variation in mouse lemurs, testing a suite of explanatory abiotic variables. Results We found substantial isotopic variation geographically. Ranges for mean isotope values were similar for both Microcebus and plants across localities (carbon 3.5–4.0‰; nitrogen 10.5–11.0‰). Mean mouse lemur and plant isotope values were lowest in cool, moist localities and highest in hot, dry localities. Rainfall explained 58% of the variation in Microcebus carbon isotope values, and mean plant nitrogen isotope values explained 99.7% of the variation in Microcebus nitrogen isotope values. Average differences between mouse lemur and plant isotope values (carbon 5.0‰; nitrogen 5.9‰) were similar across localities. Main conclusions Isotopic data suggest that trophic differences among Microcebus populations were small. Carbon isotope values in mouse lemurs were negatively correlated with rainfall. Nitrogen isotope values in Microcebus and plants covaried. Such findings suggest that nitrogen isotope values for Microcebus are a particularly good proxy for tracking baseline isotopic differences among habitats. Our results will facilitate future comparative research on modern mouse lemur communities, and ecological interpretations of extinct Holocene communities.     

Epigenetic switches in clag3 genes mediate blasticidin S resistance in malaria parasites

Malaria parasites induce changes in the permeability of the infected erythrocyte membrane to numerous solutes, including toxic compounds. In Plasmodium falciparum, this is mainly mediated by PSAC, a broad‐selectivity channel that requires the product of parasite clag3 genes for its activity. The two paralogous clag3 genes, clag3.1 and clag3.2, can be silenced by epigenetic mechanisms and show mutually exclusive expression. Here we show that resistance to the antibiotic blasticidin S (BSD) is associated with switches in the expression of these genes that result in altered solute uptake. Low concentrations of the drug selected parasites that switched from clag3.2 to clag3.1 expression, implying that expression of one or the other clag3 gene confers different transport efficiency to PSAC for some solutes. Selection with higher BSD concentrations resulted in simultaneous silencing of both clag3 genes, which severely compromises PSAC formation as demonstrated by blocked uptake of other PSAC substrates. Changes in the expression of clag3 genes were not accompanied by large genetic rearrangements or mutations at the clag3 loci or elsewhere in the genome. These resultsdemonstrate that malaria parasites can become resistant to toxic compounds such as drugs by epigenetic switches in the expression of genes necessary for the formation of solute channels.     

Impact of the new generation coronary care unit.

A 30-bed coronary care unit with facilities for fluoroscopy, haemodynamic monitoring, mechanical heart assistance, and long-term electrocardiographic monitoring operated at a reasonable cost over five years. Much of the work was entrusted to trained nurses, and there was close consultation with cardiac surgeons over those patients who needed catheterisation or surgery. New procedures greatly reduced the numbers of early deaths from cardiac arrest and cardiac failure but had less influence on late mortality. Hospital mortality for all 3353 patients was 6-8%, and for patients under 65 with definite infarction, who were admitted direct it was 5-7%.     

The specificity of a weak gamma delta TCR interaction can be modulated by the glycosylation of the ligand.

The gamma delta T cell clone LBK5 recognizes the MHC molecule IEk. Here, we demonstrate that the affinity of this interaction is weaker than those typically reported for alpha beta TCRs that recognize peptide/MHC complexes. Consistent with our previous finding that peptide bound to the IE molecule does not confer specificity, we show that the entire epitope for LBK5 is contained within the polypeptide chains of the molecule, centered around the polymorphic residues 67 and 70 of the IE beta-chain. However, LBK5 recognition is profoundly influenced by the N-linked glycosylation at residue 82 of the IE alpha-chain. Since infected, stressed, or transformed cells often change the posttranslational modifications of their surface glycoproteins, this finding suggests a new way in which gamma delta T cell Ag recognition can be regulated.     

Root exudation and physiological status of a root-colonizing fluorescent pseudomonad in mycorrhizal and non-mycorrhizal pepper (Capsicum annuum L.)

Ultramafic (serpentine) soils from and adjacent to the Dun Mountain Ophiolitic Belt, South Island, New Zealand were analysed for 11 elements in order to establish to what degree edaphic factors influenced the character of the overlying vegetation. Using principal components analysis with a mutual plot of the first two principal components, involving the total elemental concentrations in the soils, it was possible to divide the soils into 6 virtually non-overlapping fields, each of which represented a specific vegetation community. Component 1 was essentially an ultramafic plot with heavy loadings from the elements chromium, cobalt, iron, magnesium, manganese, and nickel. Component 2 was a non ultramafic plot with heavy loadings from aluminium, copper and zinc. For elements extracted from the soils at pH 5.9, discrimination was somewhat poorer but confirmed the great importance of magnesium and nickel as controlling elements for the serpentine vegetation. It was concluded that the results indicated the overriding importance of edaphic factors in controlling the serpentine vegetation.     

Flux Analysis of Glucose Metabolism in Rhizopus oryzae for the Purpose of Increasing Lactate Yields

A flux analysis of glucose metabolism in the filamentous fungus Rhizopus oryzae was achieved using a specific radioactivity curve-matching program, TFLUX. Glycolytic and tricarboxylic acid cycle intermediates labeled through the addition of extracellular [U-14C]glucose were isolated and purified for specific radioactivity determinations. This information, together with pool sizes and the rates of glucose utilization and end product production, provided input for flux maps of the metabolic network under two different experimental conditions. Based upon the flux analysis of this system, a mutant of R. oryzae with higher lactate and lower ethanol yields than the parent was sought for and found.     

Sexual dimorphism in Odonata: age, size, and sex ratio at emergence

Males and females of many organisms differ in important life-history and behavioral characters. Following a recent optimization analysis of sexually dimorphic life histories, we employed an odonate-like parameter set to identify patterns of life history and behavior to be expected in an odonate population. The default parameter magnitudes generated a smaller body size and shorter development time for males than for females, which resulted in a male-biased sex ratio. Whether population growth was density dependent or density independent, and whether development time was fixed or flexible had major impacts on life-history features. The model generated five general predictions for odonate systems. (1) For species with fixed development times, males and females should differ more in activity level, growth and mortality rates than for species with flexible life cycles. (2) In species with fixed development times, populations at high latitude or high altitude should be more active, emerge and reproduce at smaller size and have a more male-biased sex ratio than low latitude and low altitude populations. (3) In density-dependent populations, with density dependence mediated by activity-dependent mortality, higher predation rates should increase activity levels and reduce development time in species with flexible development times. (4) For species with flexible development times, in strongly density-dependent populations with density dependence mediated by mortality, activity levels should decrease and development times should increase at high prey abundance. (5) Males should be larger at emergence relative to females, and the sex ratio at emergence should be more female-biased in territorial than in non-territorial species. Existing empirical evidence concerning these predictions is generally sparse and equivocal; focused tests are clearly needed.     

Circadian rhythms ofMacaca mulatta: Sleep,EEG, body and eye movement,and temperature

EEG, EOG, EMG, gross activity, and temperature were continuously recorded over 24 hours from 38 maleMacaca mulatta monkeys. EEG, EOG, and EMG were translated into standard Sleep Stages. The EEG also was automatically filtered, rectified, integrated, digitized, and plotted. Results are presented first as 24-hour plots for temperature, Sleep Stages Awake, 1–2, 3–4, and REM, for EMG, gross motion, EOG, and for the occurrence of EEG bands delta, theta, alpha, sigma, and beta.Twenty-four-hour cosine curves were fitted to the data by least squares, demonstrating and quantifying with confidence intervals a circadian rhythm in each function. During the 12-hour dark span the acrophases, or peaks of the cosines fitted to the data, appeared in the following clockwise order: Stage 3–4, delta, Stage 1–2, Stage REM, total EEG, and theta. The clockwise order of acrophases appearing in the light span was: alpha, gross motion, sigma, beta, EMG, EOG, temperature, and Stage Awake. Circadian amplitudes are given for each rhythm.Three of these measures of brain function had circadian rises or falls which appeared to be influenced by the daily times of light-on or -off. Lighting acted as circadian phase-synchronizing stimulus for temperature and the EEG bands beta and sigma.The data demonstrate circadian rhythms for certain parameters associated with sleep—delta, theta, Stage REM, and Stage 3–4 and important differences in phase. This finding constitutes another line of evidence that sleep is not unitary, consisting rather of related but separately controlled rhythmic functions.Considerable phylogenetic constancy appears when these data on circadian phasing are compared with similar data from other primates, including man.The experimental work was part of Aeromedical Research Laboratory Project 6892, Holloman Air Force Base, U.S.A.F. Biochemical assays were supported by the U.S.P.H.S. (MH 15413). Data analysis performed at the University of Minnesota was supported by NASA (NAS 2-2738 and NGR-24-005-006), the U.S. Air Force (F29608-69-C-0011), and by the USPHS (CA 5-K6-GM 13981). Further reproduction of this article is authorized as needed to meet the requirements of the U.S. government. The animals used in this study were handled in accordance with the Guide for Laboratory Animal Facilities and Care published by the National Academy of Science-National Research Council. Drs.Crowley andKripke were on active duty, and Dr.Pegram was a civilian employee with the USAF during part of this project.