Acid-stable cytochromes in ferrous ion oxidizing cell-free preparations from Thiobacillus ferrooxidans

Abstract Cell-free preparations from ferrous ion- and sulfur-grown Thiobacillus ferrooxidans prepared under neutral (pH 7.5) or acidic conditions (pH 2.0) were compared. Under neutral conditions the ferrous ion-oxidizing system of T. ferrooxidans was membrane-bound. At acidic conditions, the enzyme system became partially solubilized. In ferrous ion-oxidizing membranes of ferrous ion-grown cells (neutral conditions) a₁-, c- and b-type cytochromes were present. The acidic preparations contained only cytochrome a₁ and c. At least three acid-stable c-type cytochromes (M_r 60 000, 30 000 and 25 000), an acid-stable protein with non-convalently bound heme group (M_r probably rusticyanin, were detected in ferrous ion oxidizing preparations. Membranes of sulfur-grown cells prepared under neutral conditions still oxidized ferrous ions, and contained a₁-, b-, c- and in addition an aa₃-type cytochrome. Cytochrome b and aa₃ were acid-labile.     

Serological characteristics of coagulase-positive staphylococci isolated from man and animals

A simplified method allowed Staphylococcus aureus, Staph. intermedius and coagulase-positive Staph. hyicus subsp. hyicus isolated from humans, dogs, monkey, sheep, poultry, rabbits, giant rats ( Cricetomys gambianus ) and other animals to be serotyped. The nine coagulase-positive staphylococcal strains of human origin possessed thermolabile and thermostable agglutinogens. Two strains of Staph. intermedius of human and canine origins examined had agglutinogen K₁K₂. The three Staph. aureus strains isolated from African giant rats ( Cricetomys gambianus ) had agglutinogens a₅ and P common to them. The Staph. aureus strain isolated from a monkey belonged to serotype b₁, c₁, o and the caprine strain of Staph. hyicus subsp. hyicus was serotype a₅, c₁.     

Tritrophic interactions in the context of climate change: a model of grasses, cereal Aphids and their parasitoids

Biologists have been challenged to envisage the likely consequences of increases in atmospheric carbon dioxide concentrations, and the suite of accompanying environmental changes (e.g. rising temperature, changing rainfall patterns, etc.) on our biotic systems. Research to date on plant responses has been extensive, but work on herbivore responses has been less complete, and work on higher trophic levels nearly nonexistent. One group of herbivores that has been reasonably well studied is aphids, and at least for this group, researchers have even begun to investigate responses at higher trophic levels, to include parasitoids. In this paper, we develop a mechanistic mathematical model of the general interaction between grasses, cereal aphids and their parasitoids. We used this model to investigate the interacting effects of rising CO₂ and temperature. The model suggests that, while parasitoids do have an impact on the aphid colony population dynamics, they do not fundamentally alter the aphid response to climate change. The model predicts that for both aphids and their parasitoids, the population responses to combined effects of elevated CO₂ and temperature will be more similar to current ambient conditions than we might expect from the individual effects of CO₂ or temperature increases. This interaction has important consequences for the interpretation of results from experiments that study only the effect of rising CO₂.     

Population variability among three small mammal species in the semiarid Neotropics: the role of density-dependent and density-independent factors

We addressed the role of density-dependent (direct and delayed) and density-independent (precipitation) factors in shaping the dynamics of fluctuating populations of three small mammal species. Using a stepwise regression procedure, we tested the effects of nonlagged population density (log₁₀ N_t-1), lagged population density (log₁₀ N_t-2), and annual precipitation on the per capita rate of population change of Phyllotis darwini, Akodon olivaceus , and Thylamys elegans in two habitat types of a semiarid region of Chile. The most irruptive species ( P. darwini ) showed direct and delayed density-dependent effects in equatorial subpopulation, and only direct density-dependence in polar subpopulation. The per capita rates of population change of A. olivaceus showed direct density-dependent and precipitation effects in both habitats types, while T. elegans showed direct density-dependence and precipitation effects in the equatorial subpopulation but only a marginal effect of direct density-dependence in the polar subpopulation. The presence of delayed density-dependent strongly suggests the importance of biological interactions in shaping the dramatic irruptions exhibited by P. darwini.     

Leaf structure and chemical composition as affected by elevated CO2: genotypic responses of two perennial grasses

Genotypic variability was studied in two Mediterranean grass species, Bromus erectus and Dactylis glomerata , with regard to the response to CO₂ of leaf total non-structural carbohydrate concentration ([TNC]_lf), specific leaf area (SLA), and leaf carbon and nitrogen concentrations ([C]_lf and [N]_lf, respectively). Fourteen genotypes of each species were grown together on intact soil monoliths at ambient and elevated CO₂ concentrations (350 and 700 μmol mol⁻¹, respectively). In both species, the most consistent effect of elevated CO₂ was an increase in [TNC]_lf and a decrease in leaf nitrogen concentration when expressed either as total dry mass [N_m]_lf, structural dry mass [N_mst]_lf or leaf area [N_a]_lf. The SLA decreased only in D. glomerata , due to an accumulation of total non-structural carbohydrates and to an increase in leaf density. No genotypic variability was found for any variable in B. erectus , suggesting that genotypes responded in a similar way to elevated CO₂. In D. glomerata , a genotypic variability was found only for [Cst], [N_m]_lf, [N_mst]_lf and [N_a]_lf. Since [N_m]_lf is related to plant growth and is a strong determinant of plant–herbivore interactions, our results suggest evolutionary consequences of elevated CO₂ through competitive interactions or herbivory.     

Population ecology of the paddy field-dwelling fish Channa gachua (Günther) (Perciformes, Channidae) in Sri Lanka

A population of Channa gachua in a small irrigation canal that supplies rice fields was studied by monthly sampling over 2 years. The population density was positively correlated with the rainfall and varied from 0.34 to 0.95 individuals m⁻². The growth parameters of the von Bertalanffy growth equation determined on monthly size–frequency data were L_x = 179 mm total length and K =0.50. Overall male to female ratio was 0.82 and there were more females than males in the middle size classes. Spawning occurred throughout the year, but all evidence indicated enhanced breeding during major rainy periods of May to July and October to December. The length at first spawning was 102 mm, which is reached in about 20 months. Fecundity, which varied between 389 and 2130, was positively correlated with gonad weight, body weight and total length. Longevity and natural mortality were estimated as 6 years and l.27 yr⁻¹, respectively. However, 99% of the population appeared to live for only 3 years. The mean biomass, average annual production and turnover ratio of the population were 7.35 g m⁻², 12.06 g m⁻² and 1.64, respectively.     

Potential effects of elevated CO2 and changes in temperature on tropical plants

Abstract. Very little attention has been directed at the responses of tropical plants to increases in global atmospheric CO₂ concentrations and the potential climatic changes. The available data, from greenhouse and laboratory studies, indicate that the photosynthesis, growth and water use efficiency of tropical plants can increase at higher CO₂ concentrations. However, under field conditions abiotic (light, water or nutrients) or biotic (competition or herbivory) factors might limit these responses. In general, elevated atmospheric CO₂ concentrations seem to increase plant tolerance to stress, including low water availability, high or low temperature, and photoinhibition. Thus, some species may be able to extend their ranges into physically less favourable sites, and biological interactions may become relatively more important in determining the distribution and abundance of species. Tropical plants may be more narrowly adapted to prevailing temperature regimes than are temperate plants, so expected changes in temperature might be relatively more important in the tropics. Reduced transpiration due to decreased stomatal conductance could modify the effects of water stress as a cue for vegetative or reproductive phenology of plants of seasonal tropical areas. The available information suggests that changes in atmospheric CO₂ concentrations could affect processes as varied as plant/herbivore interactions, decomposition and nutrient cycling, local and geographic distributions of species and community types, and ecosystem productivity. However, data on tropical plants are few, and there seem to be no published tropical studies carried out in the field. Immediate steps should be undertaken to reduce our ignorance of this critical area.     

Altered kelp (Laminariales) phlorotannins and growth under elevated carbon dioxide and ultraviolet-B treatments can influence associated intertidal food webs

Due to the importance of brown algae, such as kelp (Laminariales, Phaeophyta), within most cool nearshore environments, any direct responses of kelp to multiple global changes could alter the integrity of future coastal marine systems. Fifty-five-day manipulation of carbon dioxide (CO₂) and ultraviolet light (UVB) within outdoor sea-tanks, approximating past, present and two predicted future levels, examined the direct influences on Saccharina latissima (= Laminaria saccharina ) and Nereocystis luetkeana development and biochemistry, as well as the indirect influences on a marine herbivore ( Tegula funebralis ; Gastropoda, Mollusca) and on naturally occurring intertidal detritivores. Kelp species displayed variable directional (negative and positive growth) and scale responses to CO₂ and UVB manipulations, which was influenced by interactions. Kelp phlorotannin (phenolic) production in blade tissues was induced by elevated UVB levels, and especially enhanced (additively) by elevated CO₂, further suggesting that some actively growing kelp species are carbon limited in typical nearshore environments. Negative indirect effects upon detritivore consumers fed CO₂-manipulated kelp blade tissues were detected, however, no statistical relationships existed among UVB-treated tissues, and test herbivores did not distinguish between phlorotannin-altered CO₂: UVB-treated kelp blade tissues. Results suggest that past and future conditions differentially benefit these kelp species, which implies a potential for shifts in species abundance and community composition. Higher CO₂ conditions can indirectly impede marine decay processes delaying access to recycled trace nutrients, which may be disruptive to the seasonal regrowth of algae and/or higher trophic levels of nearshore ecosystems.     

Measurements of photosynthesis and respiration in plants

Methods for measuring the rates of photosynthesis and respiration in plants are reviewed. Closed systems that involve manometric techniques, ¹⁴CO₂ fixation, O₂ electrodes and other methods for measuring dissolved and gas phase O₂ are described. These methods typically provide time-integrated rate measurements, and limitations to their use are discussed. Open gas exchange systems that use infra-red CO₂ gas analysers and differential O₂ analysers for measuring instantaneous rates of CO₂ and O₂ exchange are described. Important features of the analysers, design features of gas exchange systems, and sources of potential error are considered. The analysis of chlorophyll fluorescence parameters for estimating the quantum yield for O₂ evolution and CO₂ fixation is described in relation to new fluorescence imaging systems for large scale screening of photosynthetic phenotypes, and the microimaging of individual chloroplasts.     

Mitigation of adverse effects of rising CO2 on a planktonic herbivore by mixed algal diets

Putative future increase in atmospheric CO₂ is expected to adversely affect herbivore growth due to decrease in contents of key nutrients such as nitrogen and phosphorus (P) relative to carbon in primary producers including plant and algal species. However, as many herbivores are polyphagous and as the response of primary producers to elevated CO₂ is highly species-specific, effects of elevated CO₂ on herbivore growth may differ between feeding conditions with monospecific and multiproducer diets. To examine this possibility, we performed CO₂ manipulation experiments under a P-limited condition with a planktonic herbivore, Daphnia , and three algal species, Scenedesmus obliquus (green algae), Cyclotella sp. (diatoms) and Synechococcus sp. (cyanobacteria). Semibatch cultures with single algal species (monocultures) and multiple algal species (mixed cultures) were grown at ambient (360 ppm) and high CO₂ levels (2000 ppm) that were within the natural range in lakes. Both in the mono- and mixed cultures, algal steady state abundance increased but algal P : C and N : C ratios decreased when they were grown at high CO₂. As expected, Daphnia fed monospecific algae cultured at high CO₂ had decreased growth rates despite increased algal abundance. However, when fed mixed algae cultured at high CO₂, especially consisting of diatoms and cyanobacteria or the three algal species, Daphnia maintained high growth rates despite lowered P and N contents relative to C in the algal diets. These results imply that algal diets composed of multiple species can mitigate the adverse effects of elevated CO₂ on herbivore performance, although the magnitude of this mitigation depends on the composition of algal species involved in the diets.     

Age-specific survival and fecundity and their effects on the intrinsic rate of increase of Aphelinus gossypii (Hym., Aphelinidae), a parasitoid of Aphis gossypii (Hom., Aphididae)

Abstract: The age-specific survival and fecundity of female adults of the aphidophagous parasitoid, Aphelinus gossypii Timberlake (Hym., Aphelinidae), were determined at a host density of 50 Aphis gossypii Glover (Hom., Aphididae) per leaf of Ageratum houstonianum Mill each day at 25°C. The age-specific mummy production, emergence rate and sex ratio of progeny were calculated. The implication of these results in terms of potential population growth of A. gossypii and related species is discussed. The age-specific survival curve ( l _x ) of females exhibited a Type I pattern, which resulted in little difference between Σ m _x and Σ l _x   m _x . The l _x curve of males exhibited a Type II pattern, and their survival time was much shorter than that of females. Each mated female produced on average 598.9 ± 64.0 aphid mummies, and preyed on 87.9±6.2 aphids. Most of the biological performance parameters were not different significantly between mated and virgin females. The highly female-biased sex ratio of offspring produced by mated females soon after their emergence resulted in a high fecundity rate ( m _x ) during the early reproductive period. Therefore, although the sex ratio of progeny was male-biased during the entire reproductive period, the intrinsic rate of increase estimated using age-specific sex ratios was larger than that estimated using a constant sex ratio of 0.5. These results indicate that the high survival and the adaptation of producing mostly female offspring during the early reproductive period contribute much to the population increase potential of this parasitoid.     

A simple persistence condition for structured populations

The fundamental question in both basic and applied population biology of whether a species will increase in numbers is often investigated by finding the population growth rate as the largest eigenvalue of a deterministic matrix model. For a population classified only by age, and not stage or size, a simpler biologically interpretable condition can be used, namely whether R ₀, the mean number of offspring per newborn, is greater than one. However, for the many populations not easily described using only age classes, stage-structured models must be used for which there is currently no quantity like R ₀. We determine analogous quantities that must be greater than one for persistence of a general structured population model that have a similar useful biological interpretation. Our approach can be used immediately to determine the magnitude of changes and interactions that would either allow population persistence or would ensure control of an undesirable species.     

Diagnostic parameters for selecting against novel spruce (Picea abies) decline: IV. Response of photosynthesis and transpiration to SO2+NO2 exposures

The dose- and time-response effects of 3 days of 6 h day-time sequential exposures to NO₂, SO₂ and SO₂+NO₂ of 0.45–1.81 μl l⁻¹ (ppm) SO₂ and 1.50–7.65 μl l⁻¹ NO₂ on photosynthesis, transpiration and dark respiration were examined for nine Carpatho-Ukrainian half-sib families and a population from the GFR ('Westerhof') of Norway spruce [ Piecea abies (L.) Karst.], all in their 5th growing season.
SO₂+NO₂ inhibited photosynthesis and transpiration and stimulated dark respiration more than SO₂ alone. SO₂ and SO₂+NO₂ at the lowest concentrations inhibited night transpiration, but increased it at the highest concentration, the strongest effects being obtained with combined exposures. Photosynthesis of the different half-sib families was affected significantly differently by SO₂+NO₂ exposures. NO₂ alone had no effects.
Sensitivity to transpiration decline correlated negatively with branch density. Height of trees correlated postitively with decline sensitivity in the seed orchard. The distribution of photosynthesis and transpiration sensitivities over all tested half-sib families correlated negatively with the distribution of decline sensitivity of their parents in a rural Danish seed orchard. The relative photosynthesis and transpiration sensitivities may thus serve as diagnostic parameters for selecting against novel spruce decline.     

Size of the first spring generation of Helicoverpa punctigera (Wallengren) (Lepidoptera: Noctuidae) and winter rain in central Australia

Serious infestations of Helicoverpa punctigera are experienced yearly in the eastern cropping regions of Australia. Regression analysis was used to determine whether the size of the first generation in spring (G₁), which is comprised mostly of immigrants from inland Australia, was related to monthly rainfall in inland winter breeding areas. Data from two long series of light-trap catches at Narrabri in New South Wales (NSW) and Turretfield in South Australia (SA) were used in the analyses. The size of G₁ at Narrabri in each year was significantly regressed on the amount of rainfall in western Queensland and NSW in May and June. The size of G₁ at Turretfield each year was significantly regressed on the amount of rain in May, June and July in western Queensland and NSW and also in the desert of central Western Australia. Low r ² values of the regressions suggest that rainfall data for more sites, as well as biological and other physical factors, such as temperature, evaporation, and prevailing wind systems, may need to be included to improve forecasts of the potential magnitude of the infestations in coastal cropping regions.     

Distribution of C3 and C4 grasses along an altitudinal gradient in Central Argentina

The distribution pattern of C₃ and C₄ grasses was studied in eight sites located between 350 m and 2100 m along an altitudinal gradient in Central Argentina. Of 139 taxa fifty-nine are C₃ and eighty C₄. Species of the C₃ tribes (Stipeae, Poeae, Meliceae, Aveneae, Bromeae and Triticeae) and C₃ Paniceae species increase in number at higher elevations; only one C₃ species was found below 650 m. C₄ Aristideae, Pappophoreae, Eragrostideae, Cynodonteae, Andropogoneae and Paniceae increase at lower altitudes. The floristic crossover point is at about 1500 m; the ground cover cross-over point is at about 1000 m. Analysis of the relationships between % C₄ species along the gradient and nine climatic and environmental variables showed the highest correlation with July mean temperature, but all temperature variables show highly significant correlations with % C₄. Correlation with annual rainfall is lower but also significant. These results are consistent with previous research showing the relative importance of C₄ grasses as temperature increases. C₃ species make a high contribution to relative grass coverage below the C₃/C₄ floristic crossover point but are rare below 1000 m.     

Elevated CO 2and water supply interactions in grasslands: a pastures and rangelands management perspective

Water is a key variable driving the composition and productivity of pastures and rangelands, and many of the ecosystems in these grasslands are highly sensitive to changes in water supply. The possibility that elevated CO₂ concentrations may alter plant water relations is therefore particularly relevant to pastures and rangelands, and may have important consequences for grassland ecosystem function, water use, carbon storage and nutrient cycling. The planning of effective research to better understand these changes requires attention to both: (i) gaps in knowledge about CO₂ and water interactions, and (ii) knowledge of how precisely the effects of CO₂ must be understood in relation to other factors, in order to predict changes in grassland structure and production. A recent microcosm experiment illustrates that non-linear effects of CO₂ and water stress could perturb primary production by triggering changes in grassland community composition. The magnitudes of the effects of CO₂ on key grassland ecosystems remain to be precisely determined through ecosystem-level experiments. A simplified simulation of the impact of different levels of productivity change in a water-limited Australian rangeland system was conducted by varying effects of CO₂ on radiation and water use efficiency. The results indicate that direct effects of CO₂ may be moderated at the enterprise scale by accompanying changes in adaptive management by farmers. We conclude that future research should aim to construct quantitative relationships and identify thresholds of response for different grassland systems. The sensitivity of these systems to management (such as grazing pressure) should also be considered when developing integrated predictions of future effects of CO₂ on water supply to grassland ecosystems.     

Sibling cannibalism among juvenile vundu under controlled conditions. II. Effect of body weight and environmental variables on the periodicity and intensity of type II cannibalism

Cannibalism among starved groups of juvenile (19–48 days old) vundu catfish Heterobranchus longifilis was 66·5% nocturnal, and its impact under modified day length was proportional to the duration of the dark phase. Shallow depth and high population density decreased the intensity of cannibalism, whereas low density and deeper environments had an opposite effect. The presence of refuges had no significant effect on cannibalism. The maintenance ( R _maint) and maximum ( R _max) daily food rations (% day⁻¹) of cannibals feeding on live prey were modelled as R _maint=3·899 W _C^0·327 ( r ²=0·684; d.f.=31), and R _max=49.545 W _C^0·321 ( r ²=0·999; d.f.=5), where W _C was the body weight of the cannibal (g). The latter model indicated that the impact of a cannibal on a population decreased by a 20% margin each time the cannibal doubled its body weight, and suggested that cannibalism among vundu would become insignificant for cannibals heavier than 30 g. The significance of these findings is discussed within the contexts of vundu aquaculture and of general, conceptual models of the dynamics of cannibalism among fishes.     

The use of compound continuous flow diffusion chemostats to study the interaction between nitrifying and nitrate-reducing bacteria

Abstract The interactions occuring between populations of a nitrate-respiring Vibrio sp. and autotrophic nitrifying bacteria belonging to the genera Nitrosomonas and Nitrobacter have been investigated in a compound bi-directional flow diffusion chemostat at a dilution rate of 0.025 h⁻¹ and a temperature of 25°C. When grown under NO⁻₃ limitation, the Vibrio sp. produced NH⁺₄ as the principal end-product of nitrate respiration, and there was a corresponding significant increase in cell numbers of the Nitrosomonas sp. population, which derived energy by the oxidation of NH⁺₄ to NO⁻₂. Nitrite in turn was used by the Nitrobacter sp. population as an energy source with the concomitant regeneration of NO⁻₃. Under NO⁻₃ excess growth conditions the Vibrio sp. produced NO⁻₂ rather than NH⁺₄ as the major product of NO⁻₃ dissimilation, and growth of the Nitrobacter population was stimulated as increased quantities of NO⁻₂ became available. In contrast, the Nitrosomonas sp. population declined sharply as the energy source NH⁺₄ became limiting. These data demonstrate that defined mixed populations of obligately aerobic nitrifying bacteria and facultatively anaerobic nitrate respiring bacteria can co-exist for extended time periods and operate an internal nitrogen cycle which is energetically beneficial to both populations.     

RAT BRAIN TUBULIN: SUBUNIT HETEROGENEITY AND PHOSPHORYLATION

Abstract— Evidence for multiple forms of the α and β subunits of tubulin isolated from rat brain has been obtained by means of SDS polyacrylamide gel electrophoresis, isoelectric focusing, and SDS hydroxylapatite column chromatography. Fourteen distinct bands, localized near pH 5.4, were formed when tubulin was subjected to isoelectric focusing in a gradient established with a very narrow range ampholyte mixture. Three tubulin subunits, a₁., α₂, and β, were separated by sodium dodecyl sulfate polyacrylamide slab gel electrophoresis in a second dimension. The β subunit was more acidic than the α subunits. Brain sections were incubated in tissue culture medium containing ³²P₁ and radiolabeled tubulin was subsequently isolated and subjected to electrophoresis. Only the β subunit was labeled. All radioactivity was associated with two or three adjacent bands on isoelectric focusing gels.     

Lethal genes in O5, chromosomes of Drosophila subobscura from Europe and America

In populations of D. subobscura , a species that is know for its high chromosomal polymorphism, the O₅ inversion has a rather erratic frequency distribution in the Palearctic region. An O₅ lethal chromosomal line obtained from a Balkan population near Zanjic (South Adriatic, Montenegro, Yugoslavia) was tested for lethal allelism with other O₅ lethal chromosomal lines derived from American (USA and Chile) colonizing populations, and from the French population of Taulé. No allelism was found between the Balkan lethal gene and those from America and France. Thus, the lethal genes of the O₅ inversions are not of the same origin and it is most probable that the American colonizations did not start from the Zanjic population. The general difference in the chromosomal inversion polymorphism corroborates this conclusion. The cytological analysis confirms the assumption that all O₅ chromosomes studied are identical with respect to breakage points.