Nuclear-localized plastid DNA fragments in protozoa, metazoa and fungi

We analyzed nuclear-localized plastid-like DNA (nupDNA) fragments in protozoa, metazoa and fungi. Most eukaryotes that do not have plastids contain 40-5000 bp nupDNAs in their nuclear genomes. These nupDNA fragments are mainly derived from repeated regions of plastids and distribute through the whole genomes. A majority of nupDNA fragments is located on coding regions with very important functions. Similar to plastids, these nupDNAs most possibly originate from cyanobacteria. Analysis of them suggests that through millions of years of universal endosymbiosis and gene transfer they may have occurred in ancient protists before divergence of plants and animals/fungi, and some transferred fragments have been reserved till now even in modern mammals.     

Determination of cellular rate distributions in microbial cell populations: feeding rates of ciliated protozoa

A novel procedure is proposed for determining distributions of rate properties and correlations of rate with state properties of microbial cell populations. The procedure is novel in that it uses transient data, and thus, it does not require that the population be in balanced growth, although it requires that the population structure does not change during the short transient experiment. The procedure is applied to populations of the ciliated protozoan Tetrahymena to determine ingestion rate variability. The number of ingested microspheres per cell and the single-cell protein content-an indicator of cell size-were directly determined with dual-color flow cytometry. The proposed technique revealed the correlation pattern of the particle ingestion rate with cell size. In particular, ingestion rate was found to be positively correlated with cell size for the smaller feeding cells and to be uncorrelated with size for the larger cells. Using the fact that particle uptake from dilute particle suspensions is a Poisson random process, we determined that the coefficient of variation of the distribution of ingestion rates within the feeding population is about 50%. It was concluded that the dynamics of particle ingestion can be accurately described only if it is realized that particle ingestion rates are distributed. (c) 1993 John Wiley & Sons, Inc.     

Use of protozoa and metazoa for decreasing sludge production in aerobic wastewater treatment

Summary A new approach to decreasing sludge production in aerobic biological wastewater treatment involving use of protozoa and metazoa was tested. The dissolved organics in the two synthetic wastewaters (based on acetic acid and methanol, respectively) tested were decomposed to >90% and the biomass production was decreased by 60–80%. The total sludge yield, expressed as total suspended solids per gram chemical oxygen demand removed, was 0.17 g TSS/g COD in the system fed acetic acid, whereas it was 0.05 g TSS/g COD in the system fed methanol. The explanation for this difference was that in the system fed methanol, dispersed bacteria were obtained that were easily grazed by the protozoa and metazoa in the predator stage. In the system fed acetic acid, the bacteria formed zoogloeal flocs, which protected them from grazing in the predator stage. With both carbon sources a significant release of nitrate (> 7 mg N/l) and of phosphate (> 2.5 mg P/l) was observed in the effluent.     

Endosymbiotic interactions in anaerobic protozoa

Several aspects of the endosymbiosis of methanogenic archaea with anaerobic protozoa are reviewed. Special attention is payed to the role of hydrogenosomes and plastid-like organelles that seem to provide the substrates for the methanogenic endosymbionts. Evidence is presented that hydrogenosomes evolved several times in the various protoctistan taxa. Hydrogenosomes are seemingly different, and their common denominator is the production of hydrogen. The absence of nucleic acids and a protein-synthesizing machineny hampers the analysis of their divergent evolutionary history, and molecular genetic data argue not only for different but even a chimeric origin of the hydrogenosomes.     

Suspension feeding in ciliated protozoa: Functional response and particle size selection

The quantitative uptake of latex beads of different sizes and of live cells by 14 species of ciliates was studied. The functional response (uptake rate as function of food particle concentration) can be fitted to a hyperbolic function and this can be explained in terms of the function of the mouth apparatus. Each species shows a distinct size spectrum of particles which are retained and ingested. These size spectra may be explained by mouth morphology, and particle size selection may play a role for niche separation of coexisting ciliates. Most bacterivorous holotrich ciliates retain particles down to 0.2m and in one case down to 0.1m; they retain particles between 0.3 and 1m most efficiently. The spirotrich ciliates investigated do not retain particles smaller than 1–2m.     

Respiration rates in heterotrophic,free-living protozoa

Published estimates of protozoan respiratory rates are reviewed with the object of clarifying their value in ecological studies. The data show a surprisingly large variance when similarly sized cells or individual species are compared. This is attributed to the range of physiological states in the cells concerned. The concept of basal metabolism has little meaning in protozoa. During balanced growth, energy metabolism is nearly linearly proportional to the growth rate constant; at the initiation of starvation, metabolic rate rapidly declines. Motility requires an insignificant fraction of the energy budget of protozoans. For growing cells, metabolic rate is approximately proportional to weight^0.75 and the data fall nearly exactly on a curve extrapolated from that describing the respiration rates of poikilotherm metazoans as a function of body weight. It is conceivable that protozoan species exist with lower maximum potential growth and metabolic rates than those predicted from cell volume and the equations derived from the available data. However, the lack of information concerning the state of the cells studied prevents verification of this idea. Laboratory measurements of protozoan respiratory rates have no predictive value for protozoa in nature other than delimiting a potential range. For small protozoans, this range may, on an individual basis, represent a factor of 50.     

Selective feeding by protozoa: model and experimental behaviors and their consequences for population stability

Selective feeding by zooplankton can have profound consequencesfor the stability of grazer and prey populations, as demonstratedby the behavior of plankton dynamics models. We present an analyticalapproach—calculation of prey ratio trajectories—thatreveals unambiguously whether selective feeding behavior isstabilizing (i.e. provides a refuge for preferred prey speciesat low prey concentrations) or destabilizing (i.e. results inelimination of prey populations). Prey ratio trajectories werecalculated for three modeled selective feeding behaviors. Constantselection was consistently destabilizing, while selection behaviorsthat changed inresponse to either prey ratio or prey abundancecould be stabilizing. Batch culture experiments with four protozoangrazer species (three ciliates, one heterotrophic dinoftagellate)demonstrated that protozoa fed selectively in every case, weaklypreferring the larger of the two algal species offered. Stabilizingselection was observed only in the experiment with Favella sp.,however, meaning that only this species altered its selectionbehavior in response to changing experimental conditions. Becauseprotozoa are the major grazers of phytoplankton in many planktonicsystems, our findings indicate that the use of selective feedingbehaviors to stabilize plankton dynamics models needs carefulevaluation. The modeling and graphical techniques presentedhereare a tool for linking further exploration of selective feedingbehaviors with the development of planktondynamics models.     

Filtering and feeding rates of cyclopoid copepods feeding on phytoplankton

The algal biomass ingested by omnivorous cyclopoid copepods (Cyclops kolensis and C. vicinus) was measured by two methods in the hypertrophic Heiligensee in Berlin (West Germany). The clearance and ingestion rates inferred from measurements of natural populations of ¹⁴C labelled phytoplankton were compared with those obtained from chlorophyll a determinations using the presence/absence method (observed chlorophyll a content of natural lake phytoplankton with and without addition of cyclopoids). Both methods gave similar results. Nevertheless, the radio tracer method is preferred, mainly because the short feeding duration excludes high variations in both the food composition and food concentration that limit the presence/absence method.     

Interactions between the parasitic protozoa of small mammals

In the wild, small mammals are frequently infected with more than one parasite. Laboratory studies have revealed complex interactions between parasites and also between parasitic protozoa and viruses or bacteria. In general, infection with many parasites is accompanied by a period of immunodepression during which superimposed infections are favoured, giving rise to more intense and prolonged secondary infections while the original infection is unaffected. On the other hand, organisms that activate macrophages may protect die host against a subsequent infection. These kinds of interactions have been investigated in the laboratory using Trypanosoma musculi, T. lewisi, Giardia muris, Spironucleus muris, Babesia microti and Heligmosomoides polygyrus , all of which occur in British small mammals, suggesting that such interactions occur in the field, are worth investigating and should be considered in epidemiological studies.     

Importance of flavonoids in insect--plant interactions: feeding and oviposition

Jeffrey Harborne and colleagues have been responsible for collating the majority of data on the role of flavonoids in insect plant interactions. This article examines some of this information and assesses our knowledge about the role flavonoids play in insect feeding and oviposition behaviour. It is clear that insects can discriminate among flavonoids and that these compounds can modulate the feeding and oviposition behaviour of insects, but further work is required to understand the neural mechanisms associated with these behavioural responses. Despite the wealth of data about the diversity of flavonoids in plants, very few of these compounds have been tested against insects and their role in the evolution of host range in insect--plant interactions has yet to be determined.     

Universal temperature and body-mass scaling of feeding rates

Knowledge of feeding rates is the basis to understand interaction strength and subsequently the stability of ecosystems and biodiversity. Feeding rates, as all biological rates, depend on consumer and resource body masses and environmental temperature. Despite five decades of research on functional responses as quantitative models of feeding rates, a unifying framework of how they scale with body masses and temperature is still lacking. This is perplexing, considering that the strength of functional responses (i.e. interaction strengths) is crucially important for the stability of simple consumer–resource systems and the persistence, sustainability and biodiversity of complex communities. Here, we present the largest currently available database on functional response parameters and their scaling with body mass and temperature. Moreover, these data are integrated across ecosystems and metabolic types of species. Surprisingly, we found general temperature dependencies that differed from the Arrhenius terms predicted by metabolic models. Additionally, the body-mass-scaling relationships were more complex than expected and differed across ecosystems and metabolic types. At local scales (taxonomically narrow groups of consumer–resource pairs), we found hump-shaped deviations from the temperature and body-mass-scaling relationships. Despite the complexity of our results, these body-mass- and temperature-scaling models remain useful as a mechanistic basis for predicting the consequences of warming for interaction strengths, population dynamics and network stability across communities differing in their size structure.     

Assisted feeding for small herbivores

Force-feeding or syringe-feeding is a necessary skill in the care and maintenance of small herbivores. The ability to supply dietary energy to a rabbit, chinchilla or guinea pig is as important as the ability to administer medication. Anyone involved in the care of small herbivores must be comfortable with and accustomed to the process of restraint and administration of force-fed supplementation.     

A candidate U1 small nuclear RNA for trypanosomatid protozoa.

In trypanosomatid protozoa, all mRNAs obtain identical 5'-ends by trans-splicing of the 5'-terminal 39 nucleotides of a small spliced leader RNA to appropriate acceptor sites in pre-mRNA. Although this process involves spliceosomal small nuclear (sn) RNAs, it is thought that trypanosomatids do not contain a homolog of the cis-spliceosomal U1 snRNA. We show here that a trypanosomatid protozoon, Crithidia fasciculata, contains a novel small RNA that displays several features characteristic of a U1 snRNA, including (i) a methylguanosine cap and additional 5'-terminal modifications, (ii) a potential binding site for common core proteins that are present in other trans-spliceosomal ribonucleoproteins, (iii) a U1-like 5'-terminal sequence, and (iv) a U1-like stem/loop I structure. Because trypanosomatid pre-mRNAs do not appear to contain cis-spliced introns, we argue that this previously unrecognized RNA species is a good candidate to be a trans-spliceosomal U1 snRNA.     

Food,feeding rates and assimilation in woodland snails

Summary Analyses of the faeces of seven species of woodland, litterdwelling snails (Marpessa laminata, Clausilia bidentata, Oxychilus cellarius, O. alliarius, Discus rotundatus, Arianta arbustorum and Hygromia striolata), showed that all feed predominently on higher plant material, be it living or dead. H. striolata and A. arbustorum took more chlorophyll-containing plant material than the other species, D. rotundatus had a significant amount of fungus in its faeces, while the faeces of O. cellarius and O. alliarius contained significant amounts of animal material.The consumption and assimilation of a variety of foods by molluscs was studied in the laboratory using an ash-ratio technique, which had been shown to give similar results to those obtained by the standard gravimetric technique. The assimilation efficiency of the molluscs was found to be temperature independent, but ingestion rates and absolute assimilation rates were temperature dependent. The assimilation efficiency of D. rotundatus on living plant material (three field layer species) was 44.8±4.43% that of H. striolata (Urtica dioica) was 52.4±8.78% while O. cellarius and H. aspersa (on Lactuca sativa) had assimilation efficiencies of 70.2±4.40% and 53.50±6.04% respectively. The results fall within the range shown by other invertebrate groups. The assimilation efficiency of D. rotundatus on leaf litter (a mean of 49.1±1.88% on five litter types) was higher than that shown by other invertebrates, probably due to the presence of gut polysaccharidases. The assimilation on dead earthworm as animal material (86.9±2.53% with O. alliarius and 78.6±6.73% with D. rotundatus) was in the range of true carnivores. Consumption rates were more variable; Urtica dioica, amongst living material, was eaten in greatest quantity; Acer pseudoplatanus, Castanea sativa and Quercus robur litter were eaten in greater quantity than Fagus sylvatica and Carpinus betulus. Consumption was examined in terms of percentage body weight.     

Trophic interactions and population growth rates: describing patterns and identifying mechanisms

While the concept of population growth rate has been of central importance in the development of the theory of population dynamics, few empirical studies consider the intrinsic growth rate in detail, let alone how it may vary within and between populations of the same species. In an attempt to link theory with data we take two approaches. First, we address the question ''what growth rate patterns does theory predict we should see in time-series?'' The models make a number of predictions, which in general are supported by a comparative study between time-series of harvesting data from 352 red grouse populations. Variations in growth rate between grouse populations were associated with factors that reflected the quality and availability of the main food plant of the grouse. However, while these results support predictions from theory, they provide no clear insight into the mechanisms influencing reductions in population growth rate and regulation. In the second part of the paper, we consider the results of experiments, first at the individual level and then at the population level, to identify the important mechanisms influencing changes in individual productivity and population growth rate. The parasitic nematode Trichostrongylus tenuis is found to have an important influence on productivity, and when incorporated into models with their patterns of distribution between individuals has a destabilizing effect and generates negative growth rates. The hypothesis that negative growth rates at the population level were caused by parasites was demonstrated by a replicated population level experiment. With a sound and tested model framework we then explore the interaction with other natural enemies and show that in general they tend to stabilize variations in growth rate. Interestingly, the models show selective predators that remove heavily infected individuals can release the grouse from parasite-induced regulation and allow equilibrium populations to rise. By contrast, a tick-borne virus that killed chicks simply leads to a reduction in the equilibrium. When humans take grouse they do not appear to stabilize populations and this may be because many of the infective stages are available for infection before harvesting commences. In our opinion, an understanding of growth rates and population dynamics is best achieved through a mechanistic approach that includes a sound experimental approach with the development of models. Models can be tested further to explore how the community of predators and others interact with their prey.     

Culturally-transmitted feeding behaviour in primates: Evidence for accelerating learning rates

Cultural transmission implies the rapid spread of behavioural innovations when initially naïve individuals copy more informed ones. Mathematical models of transmission feature accelerating (and in most cases, logistic) rates of learning as animals that acquire an innovation provide ever increasing numbers of informers for potential learners. Conversely, non-accelerating rates have been proposed as a null hypothesis for apparent cases of cultural transmission that can best be explained by simpler mechanisms such as trial-and-error learning. Using the AIC technique for comparing models with different numbers of parameters, this paper examines the 21 cases in the primate literature where quantifiable data are available on learning rates for presumed culturally-transmitted feeding innovations. In each case, cumulative distributions over time of the frequency or proportion of individuals that acquire an innovation are compared with three accelerating functions (logistic, positive exponential, and hyperbolic sine) and two non-accelerating ones (linear and logarithmic). In 16 cases, the best fit is given by an accelerating function: nine of these support the logistic, four support the positive exponential and three, the reverse S-shaped hyperbolic sine. Individual cases often show small differences between alternative functions, but overall trends support the cultural assumption of accelerating learning rates.