Occurrence and diurnal population fluctuations of the ruminal protozoan Microcetus lappus

A series of experiments with bison and cattle were conducted to obtain information on the relatively uncommon ruminal protozoan Microcetus lappus. Although M. lappus is a holotrich, diurnal changes in concentrations indicate that it follows a cycle unlike most other holotrichs, decreasing shortly after feed is offered and then gradually increasing over time. Concentrations of M. lappus varied widely among animals, exceeding 50% of the total protozoan population in some cattle. In bison, Microcetus concentrations averaged 2% of the protozoan population. Dietary protein and energy levels apparently did not influence Microcetus numbers. The highest concentrations of M. lappus were found in the reticulum, whereas the lowest numbers occurred in the mid-dorsal sac.     

Microcetus lappus gen. nov., sp. nov.: new species of ciliated protozoon from the bovine rumen.

A new species of small, ciliated protozoon, Microcetus lappus gen. nov., sp. nov., from the rumen of Norwegian Red cattle is described. M. lappus possesses a novel cytopharyngeal apparatus of two rod-shaped structures, one situated on the dorsal side of the buccal cavity and one on the ventral side, suggesting that it belongs to a previously undescribed taxon.     

Natural variability and diurnal fluctuations within the bacteriophage population of the rumen.

To investigate the impact of nutritional and environmental factors on bacteriophage activity in the rumen, it is first valuable to determine the extent of natural variations and fluctuations in phage populations from different animal species, and from animals located together and separately, and variation in animals over time. Differences in phage populations between sheep on different diets, between sheep and goats, and within the rumen over time were investigated by using pulsed-field gel electrophoresis and comparing total phage DNA in ruminal fluid. It was found that no two individuals had similar DNA banding patterns, even when similarly fed and penned together, indicating there is considerable individual diversity in phage populations between animals. Despite these individual differences, the quantities, but not the banding patterns, of phage DNA were similar for animals within groups but varied between groups, suggesting that nutritional factors may influence overall phage activity in the rumen. In sheep fed once daily, a distinct diurnal variation in the phage population was observed. Two hours postfeeding, total phage DNA dropped to its lowest level. The phage population then increased, reaching a maximal level 8 to 10 h postfeeding before declining over the next 4 h to reach a stable concentration for the rest of the cycle. The general trend in phage DNA concentration appeared similar to previously recorded diurnal fluctuations in ruminal bacterial populations in cattle fed once daily.     

Microcetus lappus gen. nov., sp. nov.: new species of ciliated protozoon from the bovine rumen

A new species of small, ciliated protozoon, Microcetus lappus gen. nov., sp. nov., from the rumen of Norwegian Red cattle is described. M. lappus possesses a novel cytopharyngeal apparatus of two rod-shaped structures, one situated on the dorsal side of the buccal cavity and one on the ventral side, suggesting that it belongs to a previously undescribed taxon.     

Seasonal variation and diurnal fluctuations in ephemeral desert pools

The physical variables which directly affect organisms inhabiting desert ephemeral pools were examined in four pools in southeastern Utah. During the day, pools were hyperoxic (240 torr) and hypocapnic (0.07 torr) while pH and temperature increased (7.5–9.0 & 17–35 °C respectively). Conversely, predawn pool measurements were hypoxic (40 torr) and hypercapnic (3 torr). While TA increased throughout the season (from 0.4 to 1.43 meq l^–1), due largely to increased bicarbonate concentration (from 0.5 to 1.4 mmol l^–1), water osmolarity remained relatively constant. These desert ephemeral systems represent unique environmental habitats where organisms experience both diurnal and seasonal changes in numerous physical variables over short time frames.     

Chemical sympathectomy and diurnal fluctuations of noradrenaline calorigenic action in the rat

In the rat, in which a diurnal fluctuation of the sensitivity to noradrenaline was previously found, the effect of injected 6-hydroxydopamine (6-OHDA) was investigated. The heat production and catecholamines contents in the interscapular brown adipose tissue, heart and adrenals were measured. Chemical sympathectomy induces a disappearance of diurnal fluctuation in the sensitivity to injected noradrenaline. In these animals a lower capacity for heat production was found. However, a significant calorigenic effect of injected noradrenaline in 6-OHDA-treated animals was still present. In sympathectomized animals a depletion of noradrenaline from interscapular brown adipose tissue and the heart was observed. Besides, a change in adrenaline/noradrenaline ratio was found in the adrenals.     

Occurrence of restriction-modification systems in ruminal butyrate-producing bacteria

Thirty-five strains of ruminal bacteria belonging to the former Butyrivibrio fibrisolvens species were screened for the presence of site-specific restriction endonuclease and modification methyltransferase activities. Seven strains possessed endonuclease activities detectable in crude cell extracts. The recognition sequences and optimal reaction conditions for seven of them were determined. Five enzymes were found to be isoschizomers of type II endonucleases (EcoRV, NsiI, AseI (2x) and SauI), one was type IIS (FokI) and two remained unknown. The optimal reaction buffer was found to be a low ionic strength buffer and all enzymes possessed sufficient activity at 39 degrees C. The presence of DNA modification among all strains was also determined. Most of the methylation activities correlated with restriction activities, yet some strains possessed unaccompanied modification methyltransferases.     

Stochastic difference equation predictors of population fluctuations.

This paper studies the effectiveness of a class of linear statistical estimators called autoregressive and autoregressive-moving averages equations for mimicking and predicting the abundance fluctuations of three species of Drosophila censused at a pine plantation near Bogota, Colombia. A short introductory justification for the use of linear estimators is given followed by a brief discussion of the theoretical basis of statistical prediction. The assumptions of the method, fitting techniques, and use of the equations in forecasting are discussed. The mimicking ability of the equations is tested by comparing monte carlo simulations employing the fitted models to the observed fluctuations of the three species. Of the autoregressive equations fitted to each species two are judged successful and one less than successful. Autoregressive-moving averages models were found to be significantly worse predictors than the simpler autoregressive equations for these three species. The parameter estimates given by the preliminary estimation techniques are compared with the statistically efficient least squares estimates. The estimates compare well for most of the autoregressive models, but the parameter estimates for the autoregressive-moving averages models were misleading.     

An NAD(+)-dependent glutamate dehydrogenase cloned from the ruminal ciliate protozoan, Entodinium caudatum

An NAD(+)-dependent glutamate dehydrogenase (GDH; EC 1.4.1.24) was cloned from the ruminal ciliate protozoan, Entodinium caudatum. The gene had high sequence similarity to GDH genes from the Bacteroides (class)--a class of bacteria which is highly represented in the rumen. When expressed in Escherichia coli the enzyme had a high affinity for ammonia and alpha-ketoglutarate (apparent K(m) of 2.33 and 0.71 mM, respectively) and a low affinity for glutamate (apparent K(m) of 98 mM). GDH activity and GDH mRNA concentration were increased by incubating washed E. caudatum cells with ammonia and antibiotics. These results suggest that the GDH is an anabolic enzyme catalysing the assimilation of ammonia by E. caudatum in the rumen and that the gene was probably acquired by lateral gene transfer from a ruminal bacterium.     

Light control of fatty acid synthesis and diurnal fluctuations of fatty acid composition in leaves.

1. Although isolated spinach chloroplasts were almost entirely (greater than 99%) dependent on light for fatty acid synthesis, leaf discs were capable of fatty acid synthesis in the dark (up to 500nmol of 3H/h per mg of chlorophyll equivalent to approx. 400nmol of carbon/h per mg of chlorophyll), which represented 12-20% of the corresponding 'light rates'. 2. Net fatty acid accumulation by greening maize leaves occurred largely or entirely during the light period. 3. There was a diurnal fluctuation in the proportions of C18 unsaturated fatty acids in the lipids of developing spinach leaves, where an increase in the concentration of oleate during the day and a subsequent decline at night was observed; a complementary change occurred in the concentration of alpha-linolenate. The rhythm is interpreted as reflecting the continuation of oleate and linoleate desaturation at high rates when oleate synthesis is markedly decreased at night. 4. Changes in the fatty acid composition of 3-sn-phosphatidylcholine accounted for at least 60% of the total decrease in oleate over the dark period. This result is consistent with suggestions that this lipid is the substrate for the leaf microsomal oleate desaturase and an intermediate in leaf glycerolipid biosynthesis.     

Dark CO2-fixation and diurnal malic acid fluctuations in the submerged-aquatic Isoetes storkii

Summary In the leaves (but not corms) of the submerged aquatic Isoetes storkii malic acid concentration fluctuated from 22 eg g FW^-1 in the evening to 171 eg g FW^-1 in the morning. Associated with this was a change in titratable acidity of 152 eg g FW^-1 between morning and evening. ¹⁴C carbon was fixed in both the light and the dark, though the amount of carbon fixed in the light was more than that fixed in the dark. Autoradiographs show 88% of ¹⁴CO₂ fixed in the dark is recovered after 1 h, in malic acid and the remainder in one other unidentified product, whereas these two products contain less than 15% of the ¹⁴C fixed after 1 h exposure to ¹⁴CO₂ in the light. It is suggested that CAM metabolism in this aquatic species may be related to the low availability of CO₂ for photosynthesis during the day in its aquatic environment and that this metabolic pathway may prove common in the genus Isoetes.     

Seasonal fluctuations in the protozoan parasites of the centipedes Lithobius variegatusand Lithobius forficatus in a Yorkshire woodland

The seasonal variation in percentage parasitization and in the average number of individuals of Echinomera spp. in Lithobius forficatus and L. variegatus is described and discussed. It is suggested that infection by Echinomera hispida may account for the low numbers of L.forficatus in damp woodlands.
Coccidia occur only in L. variegatus and the incidence of metazoan parasites is very low.     

Nonlinear time-series modeling of vole population fluctuations

A central goal of population ecology is to understand and predict fluctuations in population numbers. Until recently, much of the debate focused on the issue of population regulation by density-dependent factors. In this paper, I describe an approach to nonlinear modeling of time-series data that is designed to go beyond this question by investigating the possibility of complex population dynamics, characterized by lags in regulation and periodic or chaotic oscillations. The questions motivating this approach are: what are relative contributions of endogenous vs. exogenous components of dynamics? Is the irregular component in fluctuations entirely due to exogenous noise, or do nonlinearities contribute to it, too? I describe the philosophy and the technical details of the nonlinear modeling approach, and then apply it to a collection of time-series data on vole population fluctuations in northern Europe. The results suggest that population dynamics of European voles undergo a latitudinal shift from stability to chaos. Dynamics in northern Fennoscandia are characterized by positive Lyapunov exponent estimates, and a high degree of short-term (one year ahead) predictability, suggesting a strong endogenous component. In more southerly populations estimated Lyapunov exponents are negative, and there is no one-step ahead predictability, suggesting that fluctuations are driven by exogenous factors.     

The spatial scale of population fluctuations and quasi-extinction risk

Using a spatially homogeneous population model with migration (random individual dispersal) and spatially autocorrelated environmental noise, we show how migration and local density regulation affect the spatial scale of fluctuations in the log of population sizes as well as the 1-yr differences in these. The difference between the squares of these two spatial scales of population fluctuations does not depend on the spatial scale of the noise but only on migration rate and strength of local density regulation. We also show how migration, local density regulation, and spatially correlated environmental noise affect the realized population process at a specific location. As the migration increases, the realized local density regulation and the expected population size increase, while the realized environmental noise decreases. This approach also enables us to analyze the dynamics of the total population size within quadrats of different sizes. The risk of local quasi extinction is strongly reduced by increasing quadrat size or migration rate, while an increase in environmental stochasticity or spatial correlation in the environmental noise increases the risk of quasi extinction.