Feeding In Planktonic Protozoans: Evidence For Non-Random Acquisition of Prey

ABSTRACT The literature on discriminant feeding by planktonic protozoans using geometric and nongeometric criteria is reviewed with emphasis on recent studies that indicate phagotrophic protists can use information other than particle size or shape to sort among potential prey. Sufficient data are available for ciliates, aplastidic microflagellates, and phagotrophic dinoflagellates. Numerous representative taxa of all three groups have chemosensory capabilities, either to specific chemicals or to prey exudates, that modify their motility patterns resulting in aggregation or dispersal. Representatives of all three groups also have specific prey preferences. These considerations imply, but do not prove, selectivity in feeding through use of chemical cues. Although prey geometry is clearly a first-order determinant of ingestion through passive mechanical selection, recent studies illustrate that planktonic ciliates and flagellates can use other criteria to discriminate among prey. the evidence clearly implicates use of chemical cues, most likely perceived through contact chemoreception. Filter feeders as well as raptors have such abilities indicating that feeding mechanisms per se do not imply limitations on feeding behavior. Evidence of considerable flexibility and complexity in chemoperceptive feeding suggests that we have only glimpsed the more detailed features of feeding behavior in aquatic protozoans.     

OF MICE AND KIN: THE FUNCTIONAL SIGNIFICANCE OF KIN BIAS IN SOCIAL BEHAVIOUR

1. Sharing recent ancestry (kinship) increases the degree of genetic similarity between individuals, where genetic similarity could mean anything from sharing a particular allele to sharing an entire genome. 2. Genetic similarity can influence behavioural and other responses between individuals in a number of ways, discriminatory and non-discriminatory. All are likely to result in kin bias, because of the correlation between genetic similarity and kinship, but only some should be regarded as involving kin discrimination. 3. Non-discriminatory kin bias could arise through close relatives sharing, for instance, physical characteristics (such as those influencing competitive ability), thresholds of behavioural response or requirements for particular resources. 4. Discriminatory kin bias could arise through the direct perception of genetic similarity between individuals (direct similarity discrimination) or the use of cues likely to correlate with genetic similarity (indirect similarity discrimination--of which kin discrimination is one form). Alternatively, it could arise incidentally through mistaken identity or discrimination at some other level, such as species identification. 5. Experiments with laboratory and wild house mice have revealed kin bias in a number of contexts, including (a) parental and infanticidal behaviour, (b) sexual development and behaviour and (c) investigatory behaviour and passive body contact among juveniles and adults. 6. While kin bias in mice has been interpreted as evidence for kin discrimination, there are several problems with such an interpretation. These include (a) pronounced and complex effects of familiarity on discrimination, (b) a high risk of error-proneness in the indirect cues used in apparent kin discrimination and (c) weak and easily disrupted kin bias effects in certain contexts. 7. Consideration of social structure and discriminatory responses within populations of wild house mice leads to an alternative explanation for some kin bias in terms of incidental discrimination based on social group membership. 8. Several results from laboratory experiments suggest incidental discrimination is a more parsimonious explanation than kin discrimination for some intrasexual kin bias in behaviour. However, kin or direct similarity discrimination appears to be the most likely explanation for other aspects of intrasexual kin bias and for intersexual kin bias.     

Diurnal Variation in Acetylene Reduction and Net Hydrogen Evolution in Five Tropical and Subtropical Nitrogen-Fixing Tree Symbioses

Diurnal variations in acetylene reduction and net hydrogen evolutionwere shown in five tropical and subtropical nitrogen-fixingtree symbioses. The symbioses studied in a growth chamber were:Acacia albida x TAL 1457, Leucaena leucocephala x TAL 1145,Prosopis chilensis x TAL 600, Casuarina glauca x HFP Cc13 andC. obesa x HFP Cc13. Acetylene reduction was highest at the end of the light periodin all symbioses studied. In the A. albida x TAL 1457 symbiosis,the diurnal variations in acetylene reduction and net hydrogenevolution showed a minor synchrony, while in the other symbiosesthe diurnal pattern of acetylene reduction and net hydrogenevolution clearly differed. Also, a diurnal variation in relativeefficiency of nitrogenase was shown in the A. albida x TAL 1457symbiosis. A hydrogen uptake enzyme was detected at a low substrate concentration(24.5 mmol m^–3 H₂) for L. leucocephala x TAL 1145, C.obesa x HFP Cc13 and has earlier been found for C. glauca xHFP CcI3. A hydrogen uptake system was also found for P. chilensisx TAL 600 and A. albida x TAL 1457 at a 17-fold higher substrateconcentration. The results show that a diurnal variation in C₂H₂ reductionand H₂ evolution occurs, and that diurnal variation in the conversionfactor between C₂H₂ reduction and N₂ fixation could occur. Thisfact raises criticisms regarding the use of a point estimateof this factor. Key words: Acetylene reduction, hydrogen evolution, uptake hydrogenase, nitrogen-fixing tree symbioses     

Photosynthesis, photorespiration and nitrogen metabolism

Abstract. The ATP and reduced ferredoxin generated in photosynthetic reactions in the chloroplast are utilized for a large number of reactions other than CO₂-fixation. Quantitatively the most important reaction is the reassimilation of ammonia liberated during photorespiration in C₃ plants via the glutamate synthase cycle. Chloroplasts are also able to reduce nitrite to ammonia, sulphate to sulphide, and synthesize a number of amino acids. The amino acids essential for human nutrition are all synthesized in the chloroplast and evidence is presented to suggest that they may be the sole site of such biosynthetic reactions.     

Carbohydrate Effects on Amino Acid Transport by Trypanosoma equiperdum*

SYNOPSIS. Uptake of ¹⁴C-labeled alanine, glutamate, lysine, methionine, proline, and phenylalanine by Trypanosoma equiperdum during 2-minute incubations occurred by diffusion and membrane-mediated processes. Amino acid metabolism was not detected by paper chromatography of trypanosome extracts. Most of 18 carbohydrates tested for ability to alter amino acid transport neither changed nor significantly inhibited transport. Glucose, however, stimulated glutamate, lysine and proline transport; fructose stimulated lysine uptake and 2-deoxy-D-glucose increased phenylalanine and methionine absorption. No evidence was found that the carbohydrates acted by binding to amino acid transport “sites.” Glucose inhibition of alanine, phenylalanine, and methionine uptake was linked to glycolysis. The rapid formation of alanine from glucose stimulated alanine release and, when glycolysis was blocked, glucose no longer inhibited alanine transport. Methionine and phenylalanine release was also stimulated by glucose. Glucose changed the ability of lysine, glutamate, and proline to inhibit each others’uptake, indicating that certain amino acids are preferentially absorbed by respiring cells. Analysis of free pool amino acid levels suggested that some amino acid transport systems in T. equiperdum are linked in such a way to glycolysis as to control the cell concentrations of these amino acids.     

Tails of Tetrahymena

SYNOPSIS. The source of force generation of beating cilia and flagella is an interaction between the doublet microtubules mediated by the dynein-1 arms which cause the doublets to slide relative to one another. Previously, we demonstrated direct sliding of Tetrahymena ciliary axonemes by dark field light microscopy. In this paper, the results of such an experiment have been captured on a polylysine-coated grid surface for whole-mount electron microscopy. Images in which sliding between doublets has taken place can be identified. We conclude that doublets slide relative to one another with a constant polarity. To produce the observed displacement, the direction of the dynein-1 arm force generation must be from base to tip, so that the doublet (n), to which the arms are attached, pushes the next doublet (n+ 1) toward the tip. In addition to the functional polarity, the dynein-1 arms are found to have a structural polarity: they tilt toward the base when viewed along the edges of the A-subfiber. A scheme is presented which reconciles the finding of a single polarity of active sliding with the geometry of microtubule tip displacement of bent cilia.     

Aspects of Scotia Sea zooplankton

Information on small scale distributions of three species of Antarctic zooplankton is reviewed. Aggregations of the euphausiid Euphausia superba , the tunicate Salpa thompsoni , and the amphipod Parathemisto gaudichaudii are compared, and the manner in which such aggregations mav arise is discussed. A possible relationship between swarming and feeding activity in E. superba is suggested in which krill are thought to be dispersed whilst feeding but that on repletion they swarm. It is thought that this may account for this species' irregular spatial distribution as recorded bv previous expeditions. A further consequence of this theory is that during the Winter swarming will be minimal.     

In vivo Chlorophyll Fluorescence Monitoring with Solid State Photosensors

Solid state photosensors with their many advantages have not been utilized for chlorophyll fluorescence research. One reason is their reputed low photosensitivity compared to photomultiplier tubes. A photodarlington sensor has a relatively low photosensitivity and a nonlinear current output versus light intensity. However, when incorporated into an apparatus described in this paper it can respond to fluorescence signals from leaves using light excitation as low as 500 μW/cm². The sensitivity of another solid state device (photovoltaic photodiode) was compared to five photomultipliers using a monochromator-microphotometer testing apparatus. This solid state sensor proved to have equal or greater sensitivity to chlorophyll fluorescence. An apparatus incorporating the photovoltaic photodiode is discussed.     

Thermal Inactivation of Plant Growth: Effects on Cotyledon Metabolism

Temperature exposures which normally decrease growth of Pisum sativum seedlings by 50 % were found to be lethal in plants whose cotyledons were removed. Utilization of the two major reserves, starch and protein, decreased at high temperatures. However, the two enzymes responsible for their hydrolysis were thermostable. It appears that the influence of high temperatures on seedling growth is not due to direct effects of temperature on cotyledon metabolism, but rather indirectly through the axis.