Numerical responses by populations of red fox and mountain hare during an outbreak of sarcoptic mange

Summary During a severe outbreak of sarcoptic mange (Sarcoptes scabiei vulpes) starting among red foxes (Vulpes vulpes) in Sweden in the 1970s, we studied: 1) the establishment and spread of the disease in northernmost Sweden (by inquiries), and 2) the 1970–84 bag records for foxes and mountain hares (Lepus timidus) (an alternative prey to the fox's main prey, voles). Since the first case of sarcoptic mange in 1975 the disease spread rapidly, with >50% of the hunting organizations having reported the disease in 1981 and >75% in 1983. Also the disease became more abundant within the areas affected. In areas with a low mange infection rate (index) the number of foxes killed in the 1980s did not deviate markedly from the average level in the 1970s. However, there was a slight tendency towards a decline in areas with a medium index and numbers declined markedly where the index was high. Hare harvests initially were low (after a tularemia epidemic) in the 1970s. In that decade harvests increased dramatically and stabilized, increased gradually or changed little, respectively, where mange infection rates were low, medium or high in the early 1980s. In areas with a low mange index hare harvests remained cyclical and at the same level in the 1980s as in most of the 1970s. However, in areas with a medium index harvests increased and seemed to begin to lose their cyclicity, and where the index was high the low and relatively stable hare harvests increased annually. A predator-prey hypothesis, assuming predators to synchronize alternative prey declines to those of the cyclic main prey, predicts that a predator reduction would cause a gradual disappearance of the cyclicity and increasing numbers among alternative prey. Our hare data are partially consistent with this prediction.     

Comparison of the effect of excessive light on chlorophyll fluorescence (77K) and photon yield of O2 evolution in leaves of higher plants

High-light treatments (1750–2000 mol photons m^–2 · s^–1) of leaves from a number of higher-plant species invariably resulted in quenching of the maximum 77K chlorophyll fluorescence at both 692 and 734 nm (F _M, 692 and F _M, 734). The response of instantaneous fluorescence at 692 nm (F _O, 692) was complex. In leaves of some species F _O, 692 increased dramatically in others it was quenched, and in others yet it showed no marked, consistent change. Regardless of the response of F _O, 692 an apparently linear relationship was obtained between the ratio of variable to maximum fluorescence (F _V/F _M, 692) and the photon yield of O₂ evolution, indicating that photoinhibition affects these two variables to approximately the same extent. Treatment of leaves in a CO₂–free gas stream containing 2% O₂ and 98% N₂ under weak light (100 mol · m^–2 · s^–1) resulted in a general and fully reversible quenching of 77K fluorescence at 692 and 734 nm. In this case both F _O, 692 and F _M, 692 were invariably quenched, indicating that the quenching was caused by an increased non-radiative energy dissipation in the pigment bed. We propose that high-light treatments can have at least two different, concurrent effects on 77K fluorescence in leaves. One results from damage to the photosystem II (PSII) reaction-center complex and leads to a rise in F _O, 692; the other results from an increased non-radiative energy dissipation and leads to quenching of both F _O, 692 and F _M, 692 This general quenching had a much longer relaxation time than reported for pH-dependent quenching in algae and chloroplasts. Sun leaves, whose F _V/F _M, 692 ratios were little affected by high-light exposure in normal air, suffered pronounced photoinhibition when the exposure was made under conditions that prevent photosynthetic gas exchange (2% O₂, 0% CO₂). However, they were still less susceptible than shade leaves, indicating that the higher capacity for energy dissipation via photosynthesis is not the only cause of their lower susceptibility. The rate constant for recovery from photoinhibition was much higher in mature sun leaves than in mature shade leaves, indicating that differences in the capacity for continuous repair may in part account for the difference in their susceptibility to photoinhibition.Abbreviations and symbols kDa kilodalton - LHC-II light-harvesting chlorophyll-protein complex - PFD photon flux density (photon fluence rate) - PSI, PSII photosystem I, II - F _O, F _M, F _V instantaneous, maximum, variable fluorescence emission - absorptance - _a photon yield of O₂ evolution (absorbed light) C.I.W.-D.P.B. Publication No. 925     

Light and acetate regulate a mitochondrial malate dehydrogenase

A malate dehydrogenase was purified from the unicellular green alga Chlorogonium elongatum Dangeard. The enzyme was localized in the mitochondria by immunogold electron microscopy and was found to be present on the cristae. The concentration of the enzyme is regulated by acetate and light. In cells cultured heterotrophically with acetate as carbon source the activity and the concentration of the enzyme is 5- to 6-fold higher than in autotrophic cells. In mixotrophically cultured cells (light and acetate) the enzyme level attains only half of the value of that in heterotrophic cells. Acetate induces an increase of the enzyme concentration while light has an inhibitory effect on this process.     

The Susceptibility of Photosynthesis to Photoinhibition and the Capacity of Recovery in High and Low Light Grown Cyanobacteria, Anacystis nidulans

The susceptibility of photosynthesis to photoinhibition and the rate of its recovery were studied in the cyanobacterium Anacystis nidulans grown at a low (10 micromoles per square meter per second) and a high (120 micromoles per square meter per second) photosynthetically active radiation. The rate of light limited photosynthetic O₂ evolution was measured to determine levels of photoinhibition and rates of recovery. Studies of photoinhibition and recovery with and without the translation inhibitor streptomycin demonstrated the importance of a recovery process for the susceptibility of photosynthesis to photoinhibition. We concluded that the approximately 3 times lower susceptibility to photoinhibition of high light than of low light grown cells, significantly depended on high light grown cells having an approximately 3 times higher recovery capacity than low light grown cells. It is suggested that these differences in susceptibility to photoinhibition and recovery depends on high light grown cells having a higher turnover rate of photosystem II protein(s) that is(are) the primary site(s) of photodamage, than have low light grown cells. Furthermore, we demonstrated that photoinhibition of A. nidulans may occur under physiological light conditions without visible harm to the growth of the cell culture. The results give support for the hypotheses that the net photoinhibitory damage of photosystem II results from the balance between the photoinhibitory process and the operation of a recovery process; the capacity of the latter determining significant differences in the susceptibility of photosynthesis to photoinhibition of high and low light grown A. nidulans.     

Calculation of leaf photosynthetic parameters from light-response curves for ecophysiological applications

Measurement of the light response of photosynthetic CO₂ uptake is often used as an implement in ecophysiological studies. A method is described to calculate photosynthetic parameters, such as the maximum rate of whole electron transport and dissimilative respiration in the light, from the light response of CO₂ uptake. Examples of the light-response curves of flag leaves and ears of wheat (Triticum aestivum cv. ARKAS) are shown.Abbreviations and symbols A net photosynthesis rate - D ¹ rate of dissimilative respiration occurring in the light - f loss factor - I incident PPFD - I effective absorbed PPFD - J rate of whole electron transport - J _m maximum rate of whole electron transport - p ^c intercellular CO₂ partial pressure - PPFD photosynthetic photon flux density - q effectivity factor for the use of light (electrons/quanta) - absorption coefficient - I ^* CO₂ compensation point in the absence of dissimilative respiration (bar) - II conversion factor for calculation of CO₂ uptake from the rate of whole electron transport - convexity factor Gas-exchange rates relate to the projective area and are given in mol·m^-2·s^-1. Electron-transport rates are given in mol electrons·m^-2·s^-1; PPFD is given in mol quanta·m^-2·s^-1.     

Stressful life events preceding the acute onset of schizophrenia: A cross-national study from the World Health Organization

This study reports on the findings from a WHO sponsored cross-national investigation of life events and schizophrenia. Data are presented from a series of 386 acutely ill schizophrenic patients selected from nine field research centers located in developing and developed countries (Aarhus, Denmark; Agra, India; Cali, Colombia; Chandigarh, India; Honolulu, USA; Ibadan, Nigeria; Nagasaki, Japan; Prague, Czechoslovakia; Rochester, USA). On a methodological level, the study demonstrates that life event methodologies originating in the developed countries can be adapted for international studies and may be used to collect reasonably reliable and comparable cross-cultural data on psychosocial factors affecting the course of schizophrenic disorders. Substantive findings replicate the results of prior studies which conclude that socioenvironmental stressors may precipitate schizophrenic attacks and such events tend to cluster in the two to three week period immediately preceding illness onset.The paper was prepared by these authors on behalf of the collaborating investigators listed on page 196.     

Characterization of a heterogeneous camel milk whey non-casein protein

A milk protein, occurring in the whey fraction, has been characterized from camel milk. Determination of the primary structure reveals the existence of two related types of chain with residue differences in at least the N-terminal region. A fragment representing an N-terminal part of the protein was also recovered (heterogeneous at the same positions). The absence of cysteine residues in the protein shows that no disulphide bridges are present. The pattern of fragments and a parent protein resembles that for casein and its fragments, showing that fragments and a multiplicity of forms may be typical for different milk proteins.     

Size selection of latex beads by blackfly larvae (Diptera: Simuliidae) in the laboratory

In laboratory experiments, blackfly larvae collected from a lake outlet, a woodland and a meadow stream were tested for size selection of latex beads of < Ito > 100 μm diameters. 3 suspensions of varying proportions for each size category were supplied to these blackfly larvae in common experiments. Comparisons between the size frequency distributions of particles supplied and the particle compositions in the larval guts showed intra- and interspecific differences and were quantified by calculating Jacobs' electivity index. In all species selection of larger particles increased with the larger larval instars. Although there was a positive selectivity of small particles in some cases, the ingested proportion of large particles increases volumes and biomasses of gut content and may be more important for larval growth than small particles.     

The quantity of protein-bound [32P]phosphotyrosine in hepatocytes and fibroblasts. The effects of tyrosine protein kinase activating agents

Tyrosine protein kinase activities have been demonstrated in transformed and normal cell systems. So far, few data on the quantity of protein-bound phosphotyrosine in intact cells have been published. A knowledge of the stoichiometric increase in phosphotyrosine in cells after hormonal induction could be of interest when evaluating the importance of the tyrosine protein kinase activities found. By the addition of a known amount of unlabeled phosphotyrosine to the precipitated protein of 32P-phosphate-labeled cells it was possible after alkaline hydrolysis to spectrophotometrically follow the phosphotyrosine during consecutive chromatographies of the material. From the specific radioactivity of the purified phosphotyrosine the initial concentration of [32P]phosphotyrosine could be calculated. The method proved to be useful for the determination of [32P]phosphotyrosine is small amounts of cells. The minimum detectable amount of [32P]phosphotyrosine was about 1 pmol, and as an example, only 2.5 X 10(6) fibroblasts were needed. By this method it was shown that platelet-derived growth factor increased protein-bound [32P]phosphotyrosine from 600 to 3,200 pmol/g of fibroblasts, while insulin only increased the [32P]phosphotyrosine from 110 to 120 pmol/g of hepatocytes.