Zooplankton impacts on chlorophyll and transparency in Onondaga Lake,New York,USA

The transparency of polluted, hypereutrophic Onondaga Lake, New York, USA has improved substantially in the late 1980's as a result of reductions in phytoplankton biomass, in the absence of significant reductions in external phosphorus loading. Much of this improvement has been due to the occurrence of clearing events, e.g. sudden and dramatic increases in transparency. Field measurements, laboratory experiments, and modelling analyses were utilized to identify processes regulating phytoplankton standing crop during the spring to fall interval of 1987. Changes in the zooplankton community documented over the past decade support the conclusion that increased zooplankton grazing has contributed to improvements in transparency. Herbivores now represent a greater fraction of the zooplankton population and more efficient cladocerans are present in greater numbers. Biomanipulation practices, e.g. reestablishment of piscivorous species, designed to reduce the abundance of planktivorous fish species in Onondaga Lake, may serve to reduce pressure on the grazing community and thus result in further improvements in transparency.     

Neue Aspekte zur zugzeitlichen Frugivorie der Gartengrasmücke (Sylvia borin)

Zusammenfassung Freilandbeobachtungen und frühere Laboruntersuchungen (Berthold 1976) führten bisher zu einer widersprüchlichen Bewertung der zugzeitlichen Frugivorie bei der Gartengrasmücke. Deshalb wurden das Wahlverhalten gegenüber verschiedenen Beeren und Früchten in deren natürlichem Gehänge in einer Voliere geprüft sowie die Auswirkung unterschiedlich frugivorer Ernährung auf Körpermasse und tägliche Nahrungsaufnahme unter kontrollierten Laborbedingungen untersucht. Zwischen dem Präferenzverhalten gegenüber bestimmten Beeren und Früchten und deren Profitabilität bzw. Nährstoffgehalt bestand kein eindeutiger Zusammenhang. Demnach ist die Wahl zwischen verschiedenen Vegetabilien nicht einfach abhängig von ihrer Größe oder dem Nährstoffgehalt. Erhebliche Unterschiede zwischen den getesteten Beeren und Früchten zeigten sich bei der täglichen Aufnahmerate und den Auswirkungen auf die Körpermasse. Während bestimmte Beeren nur als Zusatzfutter zu einem immer, wenn auch geringfügig notwendigen, animalischen Standardfutter verabreicht werden konnten, waren die Gartengrasmücken mit Schwarzem Holunder und Feige auch bei ausschließlicher Gabe nicht nur in der Lage, ihre Körpermasse zu halten, sondern konnten dabei sogar normale Fettdeposition vollziehen. Offensichtlich sind bestimmte Vegetabilien für die Gartengrasmücke wesentlich bedeutsamer als bisher angenommen. Die Ergebnisse stimmen somit mit Beobachtungen aus dem Freiland überein. Die beobachteten qualitativen Unterschiede zwischen den Früchten und deren Wirkung auf die Körpermasse der Versuchsvögel ließen sich nicht allein mit dem Nährstoffgehalt der Beeren erklären. Vermutlich spielen die spezifische Qualität der Nährstoffe (z. B. Fettsäurezusammensetzung) und möglicherweise auch sekundäre Pflanzenstoffe eine wichtige Rolle.

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The significance of seasonal frugivory in migratory Garden WarblersSylvia borin

Summary In contrast to field observation, exhibiting an important role of seasonal frugivory,Berthold (1976) concluded that fruits are only a supplementary food, and he rejected the hypothesis that songbirds shift to a fruit diet during migration in order to render or to accelerate fat deposition.We investigated the preference of Garden Warblers upon various berries and pulpy fruits in an outdoor aviary. Furthermore, the effects of frugivory on body mass and food intake is measured in caged specimens under controlled laboratory conditions.In almost all feeding trials a significant selection between the two alternative fruit diets are obvious. However, no clearcut relationship between profitability or nutritive content of the various fruits and food choice is evident.In the experiments under controlled laboratory conditions the effects of varying extends of frugivory on body mass and food intake of captive Garden Warblers reveal a considerable difference between various berries and fruits. In some berries, the birds were not able to compensate for a reduction of the standard animal food by increasing frugivory. With Black Elder berries or figs, however, they did not only compensate for to maintain body mass rather they were able to gain mass during migratory fat deposition, even kept on an exclusive fruit diet.These results clearly exhibit a significant role of fruit diets in migrating Garden Warblers, with particular regards to Black Elder berries and figs, respectively.The observed differences between the various fruit diets do not correspond to the crude nutritive content of the pulp. Presumably, the specific quality of nutrients (for instance, fatty acid composition) or even secondary plant compounds have to be considered.The experimental results agree with field observations, indicating the importance of frugivory for the Garden Warbler, and they contradict Berthold's suggestion that fruits are only a least important supplementary food to an always necessary animal food.

     

Neutrophil hyperpolarization in response to a chemotactic peptide

The chemotactic peptide formylmethionyl-leucyl-phenylalanine (fMLP), at concentrations below 10(-9) M, elicits a sustained increase in the human neutrophil's membrane potential within 10 s of its addition. This hyperpolarization, detected with the fluorescent cationic potentiometric probes, 3,3'-dipentyloxacarbocyanine (diO-C5-(3)), and 1,1'-dipropyl-3,3,3',3'-tetramethylindocarbocyanine iodide (diI-C3-(3)), and with the anionic probe bis-(1,3-diethylthiobarbituric)trimethine oxonol (bis-oxonol), is immediately followed by a large depolarization when [fMLP] greater than 10(-9) M. By extracellular substitution of sodium ions with potassium ions or choline or by pretreatment of the cells with ionophores, we report here that the hyperpolarization is primarily dependent on an intact potassium ion gradient and is accompanied by a concurrent acidification of the cytoplasm (approximately 0.05 pH unit) Although the latter occurs simultaneously with a large, transient increase in cytosolic Ca2+ at [fMLP] greater than 10(-10) M, it occurs without a detectable increase in cytosolic Ca2+ at [fMLP] less than 10(-10) M. The hyperpolarization is neither affected nor initiated by the chemotactic peptide antagonist tert-butyloxycarbonyl-methionyl-leucyl-phenylalanine, whereas the depolarization is completely inhibited. Neutrophils isolated from patients with X-linked chronic granulomatous disease exhibit normal hyperpolarizations and cytosolic Ca2+ increases in response to chemotactic peptides but exhibit no depolarization or oxidative burst. The hyperpolarization appears earlier in the ontogeny of differentiating myeloid precursor cells than either the rise in cytosolic Ca2+ or the depolarization response. Together, these findings indicate that an increase in transmembrane potential is one of the earliest events in the neutrophil response to chemotactic peptides, coinciding temporally with increases in cytoplasmic Ca2+ and H+ concentrations but preceding detectable oxidative burst activity.     

Analysis in vivo of translational mutants of the rIIB cistron of bacteriophage T4

We have mapped the mutants isolated by Nelson et al. (1981) that reduce the amount of rIIB protein synthesized during bacteriophage T4 infection of Escherichia coli B and characterized their rIIB expression in vivo. These mutants fall into four distinct groups in terms of mapping and phenotype. We have located the probable site of each mutation on the DNA sequence. We have also analyzed a number of other mutations near the initiating AUG of rIIB with respect to their rIIB expression. In some of these mutants, ribosomal recognition of the wild-type initiating AUG is precluded and so initiation occurs at a different AUG, which, in some instances, we have identified.     

Ultrastructural changes in the endoplasmic reticulum during dormancy release of apple embryos (Pyrus malus L.)

Apple embryos were treated by cold (0°C) within the fruits, to break their dormancy; the controls were treated at 12°C or at 20°C. Ultrastructural features of meristematic cells in the embryonic axis were compared for each treatment. The organization of the cells of dormant embryos was described: Endoplasmic reticulum consisted in some short rough cisternae; lipid droplets regularly arranged near the plasmalemma constituted a kind of shell; mitochondria had a few cristae; and dictyosomes were rarely observed. All these features are typical of dry seeds. After cold treatments, the only evolution observed was in the endoplasmic reticulum, where highly organized stacks appeared progressively as a function of time at 0°C. An intermediate temperature (12°C) induced similar formations in the reticulum but they were rarely observed and their degree of organization was lower than that obtained at 0°C. At 20°C, endoplasmic reticulum resembled that of the dormant embryo cells. The relation between the appearance of these structures in the reticulum and the disappearance of dormancy induced by cold is discussed.Abbreviations ER endoplasmic reticulum - RER rough endoplasmic reticulum     

Preparation and application of a photoreactive thrombin analogue: binding to human platelets

alpha-Thrombin has previously been shown to bind to specific, saturable glycoproteins on the platelet surface. Modification of the thrombin active site with tosyllysyl chloromethyl ketone (TosLysCH2Cl) does not alter thrombin's binding characteristics. Interaction of alpha-thrombin with high-affinity binding sites (KD = 10(-9) M) initiates the platelet response which involves proteolytic hydrolysis of this glycoprotein. Although TosLysCH2Cl--thrombin binds to and competes for the same sites as alpha-thrombin, it cannot induce platelet stimulation because it is enzymatically inactive. In this study, we describe the preparation and application of photoreactive tritium-labeled thrombin analogues. The alpha-thrombin derivative retains its platelet-stimulating and enzymatic activities and, upon photoactivation, covalently binds to specific platelet membrane components. When freshly washed human platelets are exposed to less than saturation doses (less than or equal to 2 nM) of the thrombin derivatives in the dark and photoactivated, a single labeled complex is detected. The same experiment with greater than saturating doses (greater than or equal to 20 nM) of the thrombin derivative yields a similar complex as well as two additional ones. Molecular weight estimates of these thrombin-bound complexes were obtained by gel filtration and NaDodSO4--polyacrylamide gel electrophoresis. The low dose (high affinity) complex with TosLysCH2Cl--thrombin has an approximate molecular weight of 200 000, while that with active alpha-thrombin is smaller, approximately 120 000, due to enzymatic cleavage. The additional complexes detected with the high thrombin dose had estimated molecular weights of 400 000 and 46 000, respectively, and appeared to be the same for TosLysCH2Cl--thrombin and for the alpha-thrombin coupled platelets. These isolated complexes appear to correspond to the two previously detected populations of thrombin binding sites on the platelet.     

Micropithecus clarki, a small ape from the Miocene of Uganda.

Micropithecus clarki, from Miocene sediments of Napak, Uganda, is the smallest known hominoid primate, living or fossil. In facial morphology it is very similar to extant gibbons. Dentally, it is most similar to the small apes from the Miocene of Kenya, Dendropithecus and Limnopithecus. All of the apes from the early Miocene of East Africa seem to represent a single phyletic group that could be easily derived from the Oligocene apes known from the Fayum of Egypt. Pliopithecus from the Miocene of Europe is more closely allied with the Oligocene radiation than with the later East African radiation.     

The use of amino acid sequence analysis in assessing evolution

The thirteen year history of assessing evolution by amino acid sequence analysis has made apparent the limitations imposed upon this system by the finite nature of the characters. This finiteness exists on several levels and ultimately expresses itself as parallelism, back mutation and the retention of primitive characters in the sequences of proteins from present day species and the putative ancestral protein chains. Sequence analysis shares these problems with other molecular approaches, but because it is concerned both with the nucleotide substitutions in the genome and with the functional roles of proteins, it has unique advantages. For example, the large fluctuation in the rate of fixation of mutations in a protein's evolution can be detected and used to point out the unreliability of any molecular clock for estimating divergence dates. Moreover, when consideration is given to studies which assign functional significance to specific amino acid sites in a protein, changes in function during the descent of a protein can be appreciated and their significance correlated with organismal evolution.