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1.
Cameroon, a west-central African country with a ~20 million population, is commonly regarded as ‘Africa in miniature’ due to the extensive biological and cultural diversities of whole Africa being present in a single-country setting. This country is inhabited by ancestral human lineages in unique eco-climatic conditions and diverse topography. Over 90% Cameroonians are at risk of malaria infection, and ~41% have at least one episode of malaria each year. Historically, the rate of malaria infection in Cameroon has fluctuated over the years; the number of cases was about 2 million in 2010 and 2011. The Cameroonian malaria control programme faces an uphill task due to high prevalence of multidrug-resistant parasites and insecticide-resistant malaria vectors. Above all, continued human migration from the rural to urban areas as well as population exchange with adjoining countries, high rate of ecological instabilities caused by deforestation, poor housing, lack of proper sanitation and drainage system might have resulted in the recent increase in incidences of malaria and other vector-borne diseases in Cameroon. The available data on eco-environmental variability and intricate malaria epidemiology in Cameroon reflect the situation in the whole of Africa, and warrant the need for in-depth study by using modern surveillance tools for meaningful basic understanding of the malaria triangle (host-parasite-vector-environment).  相似文献   

2.
Summary CO2 assimilation in relation to light intensity and the relationship between leaf nitrogen and phosphorus concentrations and CO2 assimilation in 14 species of ecologically important Zimbabwean trees were examined. Eight of the species are members of the Fabaceae (Leguminosae). In the majority of Zimbabwean climax woodlands, the dominant trees are non-nodulating members of the sub-family Caesalpinioideae. The species examined have higher light saturation points (>700 mol m–2 s–1) than woody species from temperate areas; one species, Acacia nigrescens, did not reach saturation at photon fluxes greater than 1500 mol m–2 sec–1. Higher leaf nitrogen content was found to correlate positively with higher CO2 assimilation rates (r=0.85; P0.0003); there was no correlation between leaf phosphorus content and CO2 uptake rates. There were no significant differences between sites in terms of leaf nitrogen or phosphorus content, but the mean photosynthetic rate at one of the sites (Chizedzi) was lower. Taxa from the nodulating legumes were found to have higher leaf nitrogen contents (309.1±SD 22 mmol m–2) than those of the non-nodulating species (239±33); the lowest nitrogen contents were found in nonleguminous trees (179±42), with the exception of Ziziphus mucronata. This species may form an association with an N2-fixing actinomycete.  相似文献   

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The water potentials of frozen leaves of Afroalpine plants were measured psychrometrically in the field. Comparison of these potentials with the osmotic potentials of an expressed cellular sap and the water potentials of ice indicated almost ideal freezing behaviour and suggested equilibrium freezing. On the basis of the osmotic potentials of expressed cellular sap, the fractions of frozen cellular water which correspond to the measured water potentials of the frozen leaves could be determined (e.g. 74% at -3.0° C). The freezing points of leaves were found to be in the range between 0° C and -0.5° C, rendering evidence for freezing of almost pure water and thus confirming the conclusions drawn from the water-potential measurements. The leaves proved to be frost resistant down to temperatures between -5° C and -15° C, as depending on the species. They tolerated short supercooling periods which were necessary in order to start ice nucleation. Extracellular ice caps and ice crystals in the intercellular space were observed when cross sections of frozen leaves were investigated microscopically at subfreezing temperatures.Symbols T temperature - water potential Dedicated to Professor Dr. Hubert Ziegler on the occasion of his 60th birthday  相似文献   

4.
The mating system of a subsocial spider mite, Schizotetranychus miscanthi Saitō, which is closely related to Schizotetranychus longus Saitō (the long seta form of Schizotetranychus celarius (Banks) is a synonym of the latter) was studied in comparison with that of S. longus. Comparisons between nesting patterns of the two related species, S. miscanthi and S. longus revealed a difference in distribution of males among nests. Although more than one male sometimes occurred in the large nests of S. miscanthi, most nests were occupied only by a single male. On the other hand, many nests of S. longus included several males. Behavioral experiments revealed that the male and females of S. miscanthi which cohabited in a nest defended their offspring from phytoseiid predators. Observations and a census of the nesting pattern in a wild population indicate that this is the second example of biparental defense and of a subsocial life-pattern in spider mites. Differences in mating systems were experimentally demonstrated in the two species. Only a single male of S. miscanthi survived in a nest, as a result of highly aggressive male-male combat, while two males of S. longus cohabited in a nest. The mating system of the former species is thus considered as harem polygyny, while that of the latter as scramble type polygyny. Furthermore, observations by video recording and scanning electron microscopy showed that the winning male in the male-male combat in S. miscanthi often preyed on the loser, suggesting cannibalism among them.  相似文献   

5.
Indigenous belief systems and informal institutions that result in the conservation of wild species or sites exemplify biocultural conservation. The erosion of cultural beliefs and practices can have adverse, often severe, consequences for biodiversity. We explored the relationships among informal institutions, religion, and human attitudes toward sacred populations of a threatened, endemic species, Sclater’s monkey (Cercopithecus sclateri), in two communities in southeastern Nigeria. Due to habitat loss and hunting pressure across the species’ range, monkeys in these two sites live alongside people, raid farms and gardens, and are commonly viewed as pests. Using structured (n = 410) and semi-structured (n = 21) interviews, we examined factors influencing residents’ views of the monkeys, mechanisms affecting adherence to social taboos against harming monkeys, and implications for conservation. Our analyses revealed that most residents, particularly those from one community, women, and farmers, held negative opinions of the monkeys. Crop and garden raiding by monkeys had the most adverse effect on people’s attitudes. Although the adoption of Christianity weakened residents’ views regarding the no-killing taboos, continued adherence to the taboos was particularly influenced by supernatural retribution in one site and community disapproval in the other. Only one community widely conferred symbolic importance on the monkeys. Such site differences illustrate the value of local cultural understanding in conservation. Pre-intervention studies of this nature allow for the development of locally and culturally sensitive conservation programs, as well as better-informed assessments of what interventions are most likely to be effective.  相似文献   

6.
Barley (Hordeum vulgare subsp. vulgare) is an economically important diploid model for the Triticeae; and a better understanding of low-temperature tolerance mechanisms could significantly improve the yield of fall-sown cereals. We developed a new resource for genetic analysis of winter hardiness-related traits, the Nure × Tremois linkage map, based on a doubled-haploid population that is segregating for low-temperature tolerance and vernalization requirement. Three measures of low-temperature tolerance and one measure of vernalization requirement were used and, for all traits, QTLs were mapped on chromosome 5H. The vernalization response QTL coincides with previous reports at the Vrn-1/Fr1 region of the Triticeae. We also found coincident QTLs at this position for all measures of low-temperature tolerance. Using Composite Interval Mapping, a second proximal set, of coincident QTLs for low-temperature tolerance, and the accumulation of two different COR proteins (COR14b and TMC-Ap3) was identified. The HvCBF4 locus, or another member of the CBF loci clustered in this region, is the candidate gene underlying this QTL. There is a CRT/DRE recognition site in the promoter of cor14b with which a CBF protein could interact. These results support the hypothesis that highly conserved regulatory factors, such as members of the CBF gene family, may regulate the stress responses of a wide range of plant species.Communicated by J.W. Snape  相似文献   

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Phytophthora root rot (PRR) of soybean (Glycine max (L.) Merr.) is the second most important cause of yield loss by disease in North America, surpassed only by soybean cyst nematode (Wrather et al. in Can J Plant Pathol 23:115–121, 2001). Tolerance can provide economically useful disease control, conditioning partial resistance of soybean to PRR. The aims of this study were to identify new quantitative trait loci (QTL) underlying tolerance to PRR, and to evaluate the effects of pyramided or stacked loci on the level of tolerance. A North American cultivar ‘Conrad’ (tolerant to PRR) was crossed with a northeastern China cultivar ‘Hefeng 25’ (tolerant to PRR). Through single-seed descent, 140 F2:5 and F2:6 recombinant inbred lines were advanced. A total of 164 simple sequence repeat (SSR) markers were used to construct a genetic linkage map. The percentage of seedling death was measured over 2 years (2007 and 2008) in the field at four naturally infested locations in Canada and China following additional soil infestation and in the greenhouse following inoculation with Phytophthora sojae isolate. A total of eight QTL underlying tolerance to PRR were identified, located in five linkage groups (F, D1b+w, A2, B1, and C2). The phenotypic variation contributed by the loci ranged from 4.24 to 27.98%. QPRR-1 (anchored in the interval of SSR markers Satt325 and Satt343 of LG F), QPRR-2 (anchored in the interval of Satt005 and Satt600 of LG D1b+w), and QPRR-3 (anchored in the interval of Satt579 and Sat_089 of LG D1b+w) derived their beneficial allele from ‘Conrad’. They were located at chromosomal locations known to underlie PRR tolerance in diverse germplasm. Five QTL that derived beneficial alleles from ‘Hefeng 25’ were identified. The QTL (QPRR-1 to QPRR-7) that were detected across at least three environments were selected for loci stacking and to analyze the relationship between number of tolerance loci and disease loss percentage. The accumulation of tolerance loci was positively correlated with decreases in disease loss percentage. The pyramid of loci underlying tolerance to PRR provided germplasm useful for crop improvement by marker-assisted selection and may provide durable cultivar tolerance against the PRR disease.  相似文献   

11.
Aluminum (Al) toxicity to plant roots is a major problem of acidic soils. The main chemical reaction involved is Al hydrolysis. Application of lime or nitrate fertilizers to raise soil pH reduces Al toxicity but not as economically as a plant genotypes with natural tolerance against this stress. Ammonium fertilization of crops and assimilation of ammonium (even that derived from dinitrogen) are particularly acidifying of the root zone. The aims of the present study were to find genotypes of soybean tolerant to aluminum stress and identify QTL underlying that trait. Used were recombinant inbred lines (RILs) derived from the cross of ‘Essex’ by ‘Forrest’. RILs were grown in a greenhouse for 3 weeks and then transferred to hydroponics in a growth chamber. Root lengths (RL) were measured before and 72 h after Al treatment. RL before and after Al treatment were measured and used to calculate root tolerance index (RTI) and relative mean growth (RMG). RILs 1, 85, 40 and 83 had significant (P < 0.005) tolerance to Al stress judged by RL after Al, RTI and RMG. Eleven minor but significant marker–trait associations (P < 0.05) were detected using one-way ANOVA but only two major loci were significant in composite interval maps (LOD >3.0). The QTL on linkage group F (chromosome 13) was in the interval Satt160–Satt252 with a peak at 24 cM (peak LOD was 3.3). The QTL underlay 31% of trait variation and the Essex allele provided an additional 1.61 cm of root growth over 72 h in the presence of Al. The QTL on linkage group C2 (probably chromosome 4) was in the interval from Satt202 to Satt371 with a peak at 3.2 cM (peak LOD was 14.7). The QTL underlay 34% of trait variation or 1.81 cm of growth over 72 h in the presence of Al. Both loci encompassed genes implicated in citrate metabolism, a method of aluminum detoxification known to vary among soybean cultivars. Two major loci and at least nine minor loci were inferred to underlie tolerance to Al. RILs and markers may be used to select alleles that increase tolerance to soybean against Al stress.  相似文献   

12.
M. Bodner  E. Beck 《Oecologia》1987,72(3):366-371
Summary The effect of supercooling and freezing on the photosynthetic capability of representatives of the permanent frost hardy giant rosette plants Dendrosenecio keniodendron, D. brassica and Lobelia telekii, of the tropical alpine regions was investigated with the non-invasive chlorophyll a fluorescence technique. While supercooling, normal chlorophyll a fluorescence kinetics exhibiting the sequence 0, I, (D), P, S, M, were recorded, however with some retardation of both, the fast and the slow characteristics as compared to those obtained at day-time temperature. As long as the leaves remained unfrozen, the rise of the variable fluorescence F from the level 0 to P was inversely related to a drop of the temperature from about 0°C to-8°C. The increase of F with lower temperature is understood to result from a decrease of the velocity of the quenching reactions while photoreduction of the primary electron acceptor appeared to be unimpeded. The second fluorescence maximum (M), usually interpreted to indicate the commencement of the biochemical reactions of photosynthesis was consistenly to be observed during supercooling. Fluoescence induction kinetics of frozen leaves showed only fast rise to presumably F max which was not followed by a significant decay for as long as 4 min. The lack of substantial quenching indicates that in the freeze-dehydrated state neither reoxidation of the primary acceptor nor energetization of the thylakoid membrane was accomplished. This effect however was immediately and fully reserved upon thawing of the leaves when the usual fluorescence induction kinetics as well as normal rates of CO2-uptake were observed. Thus the permanent frost-hardy afroalpine plants do not exhibit any even short-term memory effect of the nocturnal frost on such a delicate process as is photosynthesis.  相似文献   

13.
Delimitation of species boundaries within the fungal genus Diaporthe has been challenging, but the analyses of combined multilocus DNA sequences has become an important tool to infer phylogenetic relationships and to circumscribe species. However, analyses of congruence between individual gene genealogies and the application of the genealogical concordance principle have been somehow overlooked. We noted that a group of species including D. amygdali, D. garethjonesii, D. sterilis, D. kadsurae, D. ternstroemia, D. ovoicicola, D. fusicola, D. chongqingensis and D. mediterranea, commonly known as D. amygdali complex, occupy a monophyletic clade in Diaporthe phylogenies but the limits of all species within the complex are not entirely clear. To assess the boundaries of species within this complex we employed the Genealogical Concordance Phylogenetic Species Recognition principle (GCPSR) and coalescence-based models: General Mixed Yule-Coalescent (GMYC) and Poisson Tree Processes (PTP). The incongruence detected between individual gene phylogenies, as well as the results of coalescent methods do not support the recognition of lineages within the complex as distinct species. Moreover, results support the absence of reproductive isolation and barriers to gene flow in this complex, thus providing further evidence that the D. amygdali species complex constitutes a single species. This study highlights the relevance of the application of the GCPSR principle, showing that concatenation analysis of multilocus DNA sequences, although being a powerful tool, might lead to an erroneous definition of species limits. Additionally, it further shows that coalescent methods are useful tools to assist in a more robust delimitation of species boundaries in the genus Diaporthe.  相似文献   

14.
Resprouting of trees and shrubs in forest-grassland ecotones is a key process to understand the dynamics of these systems under different disturbance regimes. This study integrates resprouting of grassland shrubs and pioneer forest trees (??gullivers??), burned in subtropical lowland grassland and cut in temperate highland grassland of Rio Grande do Sul, Brazil. Per grassland site, 20 individuals each of 1?C2 grassland shrub species (Asteraceae) and two forest tree species (Myrsinaceae, Myrtaceae) were tagged, and post-disturbance survival and growth monitored for 1?year at 2?C4?month intervals. Differences in resprouting vigour (summed-up basal area of resprouted shoots per pre-disturbance summed-up area of basal stems), and in density and allometry of resprouted shoots (allocation mode) were compared between tree and shrub species by linear mixed effects modelling and multiple comparisons, using the Tukey test. All grassland shrub individuals resprouted and regained 73?C142?% (species average) of pre-disturbance basal area within one year, as opposed to 14?C24?% in trees. All Myrtaceae ??gullivers?? resprouted, but up to two-thirds of Myrsine individuals did not survive disturbance. Tree species tended to produce either many slender or few stout shoots, while shrub species were intermediate between these extremes. Forest trees regained 22?C46?% of pre-disturbance height, independent of allocation mode, and grassland shrubs up to 73?%. This suggests that grassland fires allow grassland shrubs but not forest trees to persist and to grow to reproductive size. Differing sprout allocation modes may reflect allometric constraints rather than strategies to outgrow the fire-prone grass matrix.  相似文献   

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Geographic distributions of all 125 endangered and threatened animals and all 70 endangered flowering plant species were compiled and mapped by administrative territory (republics, states, provinces, and districts) of the Russian Federation, based on distributional data in the official Red Data Books of the R.S.F.S.R. [Eliseev et al. (eds) (1985) Red Book of the R.S.F.S.R.: Animals. Rosleskhoz Publishing, Moscow; Golovanov et al. (eds). (1988). Red Book of the R.S.F.S.R.: Plants. Rosagprom Publishing, Moscow]. Territories were ranked using an algorithm that gives highest rank to the single territory with the greatest number of endangered species present, then iteratively assigns the next highest rank to the territory containing the greatest number of species not found in a territory of higher rank. This algorithm minimizes the number of territories necessary to include one population of each endangered species, but may designate very low rank to a territory that holds high numbers of endangered species if many of those species are found in a territory of higher rank. When different sets of species were used to determine territory rank with this algorithm the only significant correlation between rank lists was between ranks generated when all species are used and when only species endemic to single territories were used. Mountainous territories on Russia's southern borders held the greatest numbers of endangered species and were highly ranked whether or not species occurring outside of Russia were excluded from the ranking algorithm. The Maritime state, Krasnodar state, Dagestan republic, Sakhalin province and the Jewish province all are centers of endangered species diversity that together contain 50 or more of endangered species for multiple taxonomic groups; this was the Dobson et al. [(1997) Science 275: 550–553] definition of an endangered species hot spot. These are all mountainous territories on Russia's southern border. Precise territorial ranking within the mountainous southern regions of the Southern Far East, Caucasus, and Altai/Sayan regions of southern Siberia was highly influenced by species endemic to single territories.  相似文献   

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ABSTRACT

Contemporary discussion about race has a tendency to set off out without first checking the rear view mirror. In Theories of Race and Ethnicity: Contemporary Debates and Perspectives, in contrast, Murji and Solomos identify what has and has not been covered, and so appeal at the outset for a ‘more sustained’ account of changing research agendas of race and ethnic relations. Taken as a whole, the collection allows the editors to contemplate ‘what factors explain the mobilizing power of ideas about race and ethnicity in the contemporary environment?' and whether indeed ‘it is the “real” rather than race that should be placed in quotation marks’.  相似文献   

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Summary In this paperVrikshopama a new genus of Stilbaceae withV. swetasakha as type is described, which is characterised by the production of ramosely branched conidiophores, the ultimate branches of which are fertile, cutting off one-celled, subhyaline, cylindrical conidia acropleurogenously.  相似文献   

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This paper is concerned with a Filipino psychic surgeon confronted by a particularly challenging case of a kind perhaps unprecedented in his practice. The paper describes and analyzes how the practitioner modified his usual clinical performance and adapted his actions to demands of an extremely difficult situation. The case is viewed in wider perspective relative to the significance of performative acts of healing in a pluralistic medical setting.  相似文献   

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