Effect of Viscosity on Formation and Sedimentation of Polytomella agilis Vertical Aggregates*

The response of vertical aggregates of Polytomella agilis to increased viscosity of the medium indicates that viscous resistance of the medium is a critical factor controlling the formation and sedimentation of protozoan aggregates. Aggregate formation time increased from 20 sec to 6.5 min as viscosity was increased 1.72 times. Sedimentation rate decreased about 140 μm/sec for each 10% increment in viscosity. Although there was a 60% decrease in speed of falling aggregates when relative viscosity was increased from 1.0 to 1.6, individually swimming P. agilis decreased less than 22% in speed even at a relative viscosity of 1.84 where aggregates did not form. Cells continued to accumulate near the surface by negative geotactic swimming after vertical aggregation ceased. Vertical aggregation is a cyclic process composed of 4 phases: a) accumulation-aggregation; b) aggregate sedimentation; c) ablation and dispersal; and d) negative geotaxis. Phase d is unique to motile microorganisms and only in such populations is vertical aggregation continuously selfperpetuating. Phases a-c occur with both motile and nonmotile bodies and are dependent upon viscous forces of the medium.     

Effects of Thiamine Deprivation and Replacement on the Mitochondrion of Polytomella agilis*

SYNOPSIS. Late log-phase cells of Polytomella agilis, grown with or without thiamine, were examined by electron microscopy. The mitochondrial profiles of cells cultivated in the presence of thiamine are relatively few in number and irregular in shape. The inner membranes, randomly dispersed in a light matrix, are elongated, vesicular, or branched in appearance. In vitamin-deficient cells, numerous mitochondrial profiles are evident. They have a regular circular or ovoid appearance. The inner membranes are regularly arrayed in an electron-dense matrix and generally appear elongated. By means of partial 3-dimensional reconstruction of whole cells the appearance of mitochondrial profiles in vitamin-deficient cells can be explained by the increased branching of a single structure. Following transfer of vitamin-deficient cells to complete medium, normal mitochondrial structure is attained by ∼3 hr. Reduced-minus-oxidized difference spectra of suspensions of normal and vitamin-deficient cells, grown with gentle aeration, were recorded. The concentrations of a- and b-type cytochromes are reduced by 80-90%, and c-type cytochromes are reduced by 40% in thiamine-deficient cells.     

Characterization of DNA components from some colorless algae

The DNA components of five colorless algae were characterized by their buoyant densities in cesium chloride. Two DNA components were detected in Polytoma obtusum and Polytoma uvella. Upon renaturation of the thermally denatured DNA the minor and approx. 15% of the major DNA component returned to their native densities. The buoyant densities of the major and minor DNA of P. obtusum and P. uvella are different from that of the morphologically and biochemically similar green alga Chlamydomonas reinhardtii. A major and a minor DNA component with the same buoyant densities as that of the green alga Euglena were also found in Astasia longa, which is morphologically similar to Euglena. The renaturation of the minor but not the major component was readily detectable by the change in buoyant density. Only one DNA component was detected in Polytomella agilis and Polytomella caeca. After thermal denaturation approx. 5% of each of these DNA components were renatured readily. Based on these data, the possible evolutionary origin of these colorless algae is discussed.     

Effects of thiamine deprivation on the growth and metabolism of the phytoflagellatePolytomella agilis

The effects of thiamine deprivation on the growth, respiration, and activity of several enzymes of the phytoflagellate protozoanPolytomella agilis were studied. Vitamin deprivation had no effect on the exponential growth rate; the peak population of cultures grown without thiamine was 50% of the control level. The rates of oxygen consumption in control and thiamine-deprived cultures were not significantly different from each other. The activities of pyruvate dehydrogenase and oxoglutarate dehydrogenase in vitamin-deprived cells were 14% and 30%, respectively, of the control values. In these cells, the succinic dehydrogenase activity was 10% and mitochondrial ATPase activity was twice that of control cells. Vitamin deprivation had no effect on the activities of malate dehydrogenase and isocitrate lyase, but pyruvic carboxylase activity increased fourfold. These results indicate a complex role for thiamine in the regulation of growth, respiration, and metabolism in this organism.     

Intrinsic competition between two secondary hyperparasitoids results in temporal trophic switch

Interspecific competition amongst parasitoids is important in shaping the evolution of life‐history strategies in these insects as well as community structure. Competition for hosts may occur between adult female parasitoids (‘extrinsic’ competition) or their progeny (‘intrinsic’ competition). Here, we examined intrinsic competition between two solitary secondary hyperparasitoids, Lysibia nana and Gelis agilis in cocoons of a primary parasitoid, Cotesia glomerata. Each species was allowed to sting hosts previously parasitized by the other at 24 h time intervals over the course of 144 h (6 days). When hosts were attacked simultaneously, neither species was dominant although the species to attack first won most encounters when it had a 24–48 h head start. However, after this time there was dramatic shift in the outcome with G. agilis dominating in all hosts > 72‐h old, regardless of which species had parasitized C. glomerata first. G. agilis larvae, which initially had competed with L. nana for control of C. glomerata resources, began attacking the larvae of L. nana, whereas L. nana rejected hosts with older G. agilis larvae or pupae. Effects of multiparasitism also affected the development time and adult mass of the winning parasitoid. Our results reveal a shift in the trophic status of G. agilis from C. glomerata (in younger hosts) to L. nana (in older hosts), the first time such a phenomenon has been reported in parasitoids.     

Comparative demography of sympatric populations of Lacerta vivipara and Lacerta agilis

Summary A mark-recapture study was carried out in sympatric populations of Lacerta agilis and Lacerta vivipara in the Netherlands from 1976 to 1982. In most years the age structure of both populations was pyramidal. For both species life expectation of females was higher and on average they did live longer. Hence the sex ratio for adults deviated significantly from 1.0 in favour of females. Maximum age for Lacerta vivipara was 8 years (female) and for Lacerta agilis 12 years (male). The density of both species fluctuated around 100/ha. The biomass of Lacerta agilis was twice that of Lacerta vivipara. In Lacerta vivipara the 3rd and 4th calendar year class supplied 78% of total net reproduction; in Lacerta agilis the 4th, 5th, and 6th calendar year classes supplied 68%. In both populations the population replacement rate was 2. Population turnover time was 4.83 years for Lacerta agilis and 2.81 for Lacerta vivipara. The life history strategy of the Lacerta vivipara population is compared with six other European Lacertavivipara populations.     

Patterns of daily behaviour in two lizard species Lacerta agilis L. and Lacerta vivipara Jacquin

Summary During the period May to August 1978, individuals of both Lacerta agilis and Lacerta vivipara were observed in a specially constructed out-door vivarium. The daily patterns of behaviour of the two species were recorded along with surface and air temperatures. Daily activity of both species followed a similar basic pattern but was modified by variations in the local weather. Adults of L. vivipara reached a thermal preferendum more quickly and had a longer daily activity period than adults of L. agilis. The larger L. agilis can increase its period of activity by making use of different thermal conditions in a diverse habitat with varied vegetation structure under conditions of high solar radiation. The status of viable populations of L. agilis could be maintained or enhanced by management aimed at modifying the microenvironment of the lizard's habitat.     

Studies on the growth and encystment ofPolytomella agilis

Summary Changes in cell population density, cell protein and cell carbohydrate levels of the flagellatePolytomella agilis during growth in batch cultures on a complex medium at 25° C, 18° C and 9° C were examined. At 25° C, cell protein and carbohydrate levels fell markedly during exponential population growth. At 18° C, cell protein values remained fairly constant, while cell carbohydrate increased. During growth at 9° C, both cell protein and carbohydrate increased. Changes in these cellular parameters were related to marked differences in the rates of population growth at these temperatures. The cellular locus of changes observed at 25° C was examined by centrifugal fractionation of disrupted cells on density gradients.Encystment was studied in cultures grown at 25° C. The maximum number of cysts produced was 5–10 per cent of the peak population density; the rate and degree of encystment were not increased by growth on conditioned medium or starvation. Cysts isolated from mixed populations by a centrifugal procedure remained viable, even after storage at —5° C for several weeks. The soluble proteins of separately disrupted motile and encysted forms ofP. agilis were examined and compared by disc electrophoresis.This investigation was supported by U.S.P.H.S. Grant AI-07926-02.     

Comparing and contrasting development and reproductive strategies in the pupal hyperparasitoids Lysibia nana and Gelis agilis (Hymenoptera: Ichneumonidae)

In most animals, the optimal phenotype is determined by trade-offs in life-history traits. Here, I compare development and reproductive strategies in two species of solitary secondary hyperparasitoids, Lysibia nana and Gelis agilis, attacking pre-pupae of their primary parasitoid host, Cotesia glomerata. Parasitoid larvae of both species exploit a given amount of host resources with similar efficiency. However, adults exhibit quite different reproductive strategies. Both species are synovigenic, and female wasps emerge with no mature eggs. However, G. agilis must first host-feed to produce eggs, while L. nana does not host-feed but mobilizes internal resources carried over from larval feeding to initiate oogenesis. Further, G. agilis is wingless, produces large eggs, has a long life-span, and generates only small numbers of progeny per day, whereas these traits are reversed in L. nana. Given unlimited hosts, the fecundity curve in L. nana was “front-loaded,” whereas in G. agilis it was depressed and extended over much of adult life. In L. nana (but not G. agilis), wasps provided with honey but no hosts lived significantly longer than wasps provided with both honey and hosts. Differences in the fecundity curves of the two hyperparasitoids are probably based on differing costs of reproduction between them, with the wingless G. agilis much more constrained in finding hosts than the winged L. nana. Importantly, L. nana is known to be a specialist hyperparasitoid of gregarious Cotesia species that pupate in exposed locations on the food plant, whereas Gelis sp. attack and develop in divergent hosts such as parasitoid cocoons, moth pupae and spider egg sacs. Consequently, there is a strong match between brood size in C. glomerata and egg production in L. nana, but a mismatch between these parameters in G. agilis.     

Geographic variation of life‐history traits in the sand lizard,Lacerta agilis: testing Darwin's fecundity‐advantage hypothesis

The fecundity‐advantage hypothesis (FAH) explains larger female size relative to male size as a correlated response to fecundity selection. We explored FAH by investigating geographic variation in female reproductive output and its relation to sexual size dimorphism (SSD) in Lacerta agilis, an oviparous lizard occupying a major part of temperate Eurasia. We analysed how sex‐specific body size and SSD are associated with two putative indicators of fecundity selection intensity (clutch size and the slope of the clutch size–female size relationship) and with two climatic variables throughout the species range and across two widespread evolutionary lineages. Variation within the lineages provides no support for FAH. In contrast, the divergence between the lineages is in line with FAH: the lineage with consistently female‐biased SSD (L. a. agilis) exhibits higher clutch size and steeper fecundity slope than the lineage with an inconsistent and variable SSD (L. a. exigua). L. a. agilis shows lower offspring size (egg mass, hatchling mass) and higher clutch mass relative to female mass than L. a. exigua, that is both possible ways to enhance offspring number are exerted. As the SSD difference is due to male size (smaller males in L. a. agilis), fecundity selection favouring larger females, together with viability selection for smaller size in both sexes, would explain the female‐biased SSD and reproductive characteristics of L. a. agilis. The pattern of intraspecific life‐history divergence in L. agilis is strikingly similar to that between oviparous and viviparous populations of a related species Zootoca vivipara. Evolutionary implications of this parallelism are discussed.     

Fine structure of encystment of the quadriflagellate alga,Polytomella agilis

Summary The differentiation of resting cysts of the algaPolytomella agilis was examined by electron microscopy. During encystment the free-swimming, quadriflagellate unicells lose their flagella, sink to the bottom of the culture, and form a thick cell wall. Populations of cells at various stages of encystment were collected on microscope slides placed at the bottom of the culture flasks. The mature cyst wall consists of four layers which are laid down sequentially next to the plasma membrane. Freeze-etching has shown that the first layer of wall deposited consists of fibrils which are formed partly embedded within the plasma membrane. A proliferation of rough endoplasmic reticulum and Golgi bodies is seen in early stages of encystment followed by a reduction in size or number of these organelles and of plastids in the maturing cyst. Microtubular structures, including the basal bodies, dedifferentiate and are not observed in the later stages of encystment. The redifferentiation of the swimming cell during excystment is described in the companion paper.This work was supported by grant A6353 from the National Research Council of Canada to D. L.Brown and by the Inland Waters Directorate of Environment Canada.     

A lacewing with the wanderlust: the European song species 'Maltese', Chrysoperla agilis, sp.n., of the carnea group of Chrysoperla (Neuroptera: Chrysopidae)

Abstract. A fifth European member of the Holarctic carnea sibling species group, Chrysoperla agilis, sp.n. is described. This species was initially recognized because of its unique song phenotype. Both sexes produce one type of song, characterized by a single very long volley averaging 4.5 s in duration and repeated every 9.5 s. The unit of exchange during heterosexual duets (the shortest repeated unit) is the single volley. The carrier frequency is upwardly, then downwardly, modulated during each volley. The maximum frequency is higher (around 110 Hz) than in other members of the carnea group. Each volley ends with an audible, percussive ‘rattle’. Song features vary only slightly over a large geographical range that extends from northern Iran westward to the Azores and northward to southern Switzerland. Discriminant function analysis confirms the uniqueness of the C. agilis song in comparison with nine other song species. Morphologically, the adult of C. agilis is very similar to C. carnea and C. pallida and is generally intermediate between them with respect to the size of the pretarsal basal dilation, the shape of the genital lip and chin, the colour and type of setae on the abdomen, and colour markings on the head and mouthparts. No single feature will distinguish C. agilis from either C. carnea or C. pallida, but a suite of physical attributes can be used with reasonable success. Larval morphology fails to distinguish clearly C. agilis from other song species. Ecologically, C. agilis shares an affinity for low vegetation with C. lucasina and C. carnea, and a preference for milder, Mediterranean climates with C. mediterranea. Adults undergo a colour change to pale yellowish brown during winter diapause, and eggs are laid singly rather than in groups. Based on its ecological characteristics, C. agilis may prove to be an effective agent of biological control in the agricultural fields of warmer, drier parts of southern Europe and the Middle East, where other members of the carnea group are less common or absent.     

Morphology of Giardia agilis: Observation by Scanning Electron Microscopy and Interference Reflexion Microscopy1

The flagellated protozoan, Giardia agilis, was isolated from tadpole small intestine and examined by scanning electron microscopy and interference reflexion microscopy. The general morphology of the G. agilis trophozoite is similar to G. muris and G. duodenalis, but with modifications that reflect its elongated form. Interference reflexion microscopic analysis of attachment of G. agilis reveals a pattern of focal contacts by the lateral crest of the ventral disc, the ventrolateral flange, the lateral shield, and by numerous microvillus-like appendages found along the lateral border of the trophozoite. The pattern of focal contacts was observed to be dynamic; trophozoites were observed to make and break the focal contacts in a relatively short time and to glide along the surface of the substratum without breaking focal contacts.     

A comparison by means of antisera and lectins of surface structures ofNitrobacter winogradskyi andN. agilis

Nitrobacter winogradskyi was grown autotrophically on carbon dioxide and nitrite, mixotrophically on pyruvate and nitrite, and heterotrophically on acetate and pyruvate.N. agilis was grown autotrophically on carbon dioxide and nitrite and heterotrophically on pyruvate, acetate, and yeast extract-peptone. Antisera were then prepared against these cells. Strong cross-reactions occurred between all antisera raised againstNitrobacter agilis cells in the homologous and heterologous reactions with the differently grownNitrobacter agilis cells. Similar results were obtained withN. winogradskyi; but there were differences between the heterotrophically grown cells and the autotrophically and mixotrophically grown cells. The autotrophically grown cells ofN. winogradskyi andN. agilis had nearly no immunological differences, while the cross-reactions of the heterotrophically grown cells differed strongly. So, growth conditions are of considerable influence on the serological behavior of the two bacteria tested. Of twelve lectins tested, five (fromAaptos papillata, Axinella polypoides, Cerianthus sp.,Ulex europeus, and Anti-H specific agglutinin of eel serum) agglutinated cells ofN. agilis andN. winogradskyi, indicating thatN-acetyl-glucosamine, galactose, and fucose may be present in the bacterial cell wall. Immunodiffusion showed that cells of both nitrifying organisms grown under different conditions had at least one antigenic surface structure in common.     

<i>Arthrobacter agilis</i> UMCV2 accelerates growth of <i>Pinus devoniana</i>

Pinus devoniana is one of the most widely distributed species of Pinus in Mexico, and has a relevant economic and ecological importance. In this work, the effect of inoculating juvenile P. devoniana plants with the rhizobacteria Arthrobacter agilis UMCV2, and its dimethylhexadecylamine compound was studied under greenhouse conditions. Our results showed that A. agilis UMCV2 promoted growth of P. devoniana as a result of increases on height and stem diameter, fresh weight and chlorophyll concentrations. Under our experimental conditions, the bacterial dimethylhexadecylamine compound produced an increase in the concentration of chlorophyll. These data show the feasibility of using A. agilis UMCV to significantly enhance the growth rate of P. devoniana at a greenhouse scale.     

Evaluation of the probiotic and functional potential of Lactobacillus agilis 32 isolated from pig manure

Escherichia coli is a symbiotic bacterium in humans and animals and an important pathogen of humans and animals. Prevention and suppression of E. coli infection is of great concern. In this study, we isolated a strain of Lactobacillus agilis 32 from pig manure and evaluated its biological characteristics, and found that its bacterial survival rate was 25% after 4 h of treatment at pH 2, and under the condition of 0·5% bile concentration, its survival rate exceeds 30%. In addition, L. agilis 32 has a cell surface hydrophobicity of 77·8%, and exhibits 67·1% auto-aggregation and 63·2% aggregation with Enterotoxigenic E. coli 10 (ETEC 10). FITC fluorescence labelling showed that the fluorescence intensity of cecum was significantly higher than that of duodenum, jejunum or colon (P < 0·05), but no significant difference from ileum. Lactobacillus agilis 32 bacterial culture and CFS showed average inhibition zone diameters of 14·2 and 15·4 mm respectively. Lactobacillus agilis 32 CFS treatment can significantly reduce the pathogenicity of ETEC 10. These results show that L. agilis 32 is an active and potential probiotic, and it has a good antibacterial effect on ETEC10, which provides basic research for probiotics to prevent and treat intestinal diarrhoea pathogen infection.     

Fine structure of excystment of the quadriflagellate algaPolytomella agilis

Summary Populations of mature resting cysts of the algaPolytomella agilis were purified from asynchronously encysting cultures and incubated in fresh culture medium to promote excystment. Up to 90 percent of the cysts germinated, with approximately 50 percent excysting between 3 and 7 hours of incubation. Each germinating cyst releases a single, fully differentiated, swimming cell. The entire excystment process of individual cysts was followed by light microscopy to establish the time course of release and cells at comparable stages of excystment were examined by electron microscopy. During the first 3 hours of incubation the cysts increase in size, presumably due to uptake of water, and a polarity is established in the cytoplasm which makes it possible to identify the site of subsequent release. Release involves a selective degradation of a portion of the cyst wall at this site followed by a physical rupturing of the weakened area. Details of the structural alterations in the wall and cytoplasm are described. The cytoplasmic organelles observed to dedifferentiate during encystment (preceding paper) are completely redifferentiated during excystment. The emergent cell is flagellated and possesses the elongate form typical of the swimming cell.This work was supported by grant A6353 from the National Research Council of Canada to D. L.Brown and by the Inland Waters Directorate of Environment Canada.     

Availability of food resources and habitat structure shape the individual‐resource network of a Neotropical marsupial

相似文献   

Microbodies und Diaminobenzidin-Reaktion in den Acetat-Flagellaten Polytomella caeca und Chlorogonium elongatum

Summary In two forms of acetate flagellates, the colourless Volvocale Polytomella caeca and the green Volvocale Chlorogonium elongatum, cell organelles can be demonstrated which are ultrastructurally similar to microbodies of higher organisms. The organelles do not have a close association with the endoplasmic reticulum and are located in the peripheral cytoplasm between the elongated mitochondria. In Polytomella they exhibit more or less spherical profiles in section and have a maximum diameter of approximately 0.2–0.25 . In Chlorogonium the organelles occasionally have an elongated shape and are larger than in Polytomella. Employing the electron microscopic cytochemical reagent diaminobenzidine (DAB)/H₂O₂ to localize the microbodial marker enzyme catalase in these organelles, it was found that no accumulation of the electron-opaque product occurs in the microbodies either at alkaline or neutral pH or at room temperature or 37° C. Only the cristae of mitochondria are stained with the DAB reaction caused by cytochrome oxidase and possibly by a cytochrome peroxidase.Organelles of Polytomella caeca containing catalase or cytochrome oxidase can be separated by rate centrifugation of a crude particulate fraction on a sucrose gradient (Gerhardt, 1971). The particles isolated from the peak of catalase activity show the same fine structural characteristics as the microbodies in situ do. But again, there is no detectable staining of these organelles by the DAB/H₂O₂ reaction.The identity of the microbody-like particles in Polytomella caeca and Chlorogonium elongatum with microbodies in general is deduced despite the negative results in cytochemical localization of catalase in these organelles.