呼吸道病原体如何损害猪   总被引：1，自引：0，他引：1  

Stan Done  袁森泉  肖新 《中国畜牧兽医》2003,30(2):44-45

许多类型的病毒、细菌和支原体都能影响猪的正常呼吸 ,但作为呼吸道疾病的主要病因 ,生产者和兽医只需充分认识少数致病菌。我们越来越多地掌握了这些主要病原体所产生伤害的复杂机理。因此可鉴别诊断并制定控制措施 ,也将会生产出新的和更有效的疫苗。1　病毒存在于猪体内最麻烦的呼吸道病毒是猪流感和猪繁殖与呼吸综合征 ( PRRS)病毒及 2型猪环状病毒 ( PCV2 )。1 .1　猪流感病毒 ( SIV)　 SIV可在鼻粘膜、扁桃体、淋巴结和肺部中进行繁殖。病毒的增殖始于上呼吸道内皮细胞。沿气管向下感染至肺部。此病毒侵袭支气管及其较细小的分…  相似文献   

Genetic diversity and relatedness of boreal caribou populations in western Canada     

Philip D. McLoughlin  David Paetkau  Stan Boutin 《Biological conservation》2004,118(5):593-598

We studied genetic diversity within and gene flow among six ‘threatened’ populations of boreal caribou (Rangifer tarandus caribou) inhabiting Alberta and British Columbia, Canada. Mean expected heterozygosity (H_E) across 11 loci spanned a narrow range between 0.74 and 0.79. Estimates of H_E were in the mid to high range of those typically observed in natural populations of large mammals, including caribou, and were not suggestive of any immediate threat to survival. We concluded that recent anthropogenic fragmentation of caribou range in western Canada has yet to affect genetic diversity of populations. Analysis of population structure identified a region of relatively low gene flow corresponding with the valley of the Peace River. The highest value of F_ST observed between populations on the same side of the river was 0.025, whereas the lowest value that spanned the river was 0.044. Confirming this result, an assignment test demonstrated that 96.5% of animals could be assigned to the correct side of the Peace River, though only 66.0% of animals could, on average, be assigned to populations of actual origin. Taken as a whole, our results support the existence of two discrete metapopulations bisected by the Peace River, within each of which there exist multiple populations, or at least multiple regions, which experience considerably higher levels of interchange. For caribou inhabiting the boreal plains, large rivers such as the Peace and Mackenzie may serve as biologically meaningful boundaries for managing metapopulations.  相似文献   

Aberrant overexpression of satellite repeats in pancreatic and other epithelial cancers     

Ting DT  Lipson D  Paul S  Brannigan BW  Akhavanfard S  Coffman EJ  Contino G  Deshpande V  Iafrate AJ  Letovsky S  Rivera MN  Bardeesy N  Maheswaran S  Haber DA 《Science (New York, N.Y.)》2011,331(6017):593-596

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Genetic variation underlying kernel size,shape, and color in two interspecific S. bicolor2 × S. halepense subpopulations     

Nabukalu  Pheonah  Kong  Wenqian  Cox  Thomas Stan  Pierce  Gary J.  Compton  Rosana  Tang  Haibao  Paterson  Andrew H. 《Genetic Resources and Crop Evolution》2022,69(3):1261-1281

Genetic Resources and Crop Evolution - Throughout the history of sorghum domestication, kernel traits have been subject to extensive selection. Breeding of grain sorghum is highly dependent on...  相似文献   

Radio-frequency spectroscopy of ultracold fermions     

Gupta S  Hadzibabic Z  Zwierlein MW  Stan CA  Dieckmann K  Schunck CH  Van Kempen EG  Verhaar BJ  Ketterle W 《Science (New York, N.Y.)》2003,300(5626):1723-1726

Radio-frequency techniques were used to study ultracold fermions. We observed the absence of mean-field "clock" shifts, the dominant source of systematic error in current atomic clocks based on bosonic atoms. This absence is a direct consequence of fermionic antisymmetry. Resonance shifts proportional to interaction strengths were observed in a three-level system. However, in the strongly interacting regime, these shifts became very small, reflecting the quantum unitarity limit and many-body effects. This insight into an interacting Fermi gas is relevant for the quest to observe superfluidity in this system.  相似文献   

Effects of wind-driven rainfall on stemflow generation between codominant tree species with differing crown characteristics   总被引：1，自引：0，他引：1  

John T. Van Stan II  Courtney M. SiegertDelphis F. Levia Jr.  Carrie E. Scheick 《Agricultural and Forest Meteorology》2011,151(9):1277-1286

Meteorological influences on the variability of stemflow generation can affect the hydrology, ecology and soil chemistry of wooded ecosystems, yet the effects of directional wind-driven rainfall on differential stemflow production remain relatively un-researched. This study examines the correspondence of directional wind-driven inclined rainfall with stemflow generation in individual tree crowns utilizing multiple correspondence analysis (MCA) and intrastorm observations at 5 min monitoring intervals. In general, preferential stemflow generation at Fair Hill was observed during episodes of inclined rainfall driven by wind from the east to north-northeast (33.76-101.25°). This was supported by MCAs which produced significant correspondences between stemflow production and periods of inclined wind-driven rainfall for nearly all monitored storm events. Intrastorm plots of stemflow production from dominant and subcanopy trees of each codominant species (Fagus grandifolia Ehrh. (American beech) and Liriodendron tulipifera L. (yellow poplar)) also verified this correspondence. Interspecific canopy characteristics of L. tulipifera and F. grandifolia affected crown position, canopy structural characteristics, and, thus, the canopy's response to inclined precipitation. The greater vertical canopy depth observed for F. grandifolia trees enabled them to more efficiently capture inclined rainfall for enhanced stemflow production; whereas, the greater horizontal surface area of L. tulipifera canopies enhanced their droplet capture efficiency and subsequent stemflow generation for periods of un-inclined rainfall. As inclined wind-driven rainfall occurred within a majority of rain events at this site, preferential stemflow production may be a significant process to consider when examining the spatial distribution of canopy-derived water fluxes to the forest floor of wooded catchments under similar meteorological conditions.  相似文献   

Limited impacts of extensive human land use on dominance,specialization, and biotic homogenization in boreal plant communities     

Stephen J Mayor  Stan Boutin  Fangliang He  James F Cahill  Jr 《BMC ecology》2015,15(1)

Background

Niche theory predicts that human disturbance should influence the assembly of communities, favouring functionally homogeneous communities dominated by few but widespread generalists. The decline and loss of specialists leaves communities with species that are functionally more similar. Evenness of species occupancy declines, such that species become either widespread of rare. These patterns have often been observed, but it is unclear if they are a general result of human disturbance or specific to communities that are rich in species, in complex, spatially heterogeneous environments where the problem has often been investigated. We therefore tested whether human disturbance impacts dominance/evenness of species occupancy in communities, specialism/generalism of species, and functional biotic homogenization in the spatially relatively homogeneous, species poor boreal forest region of Alberta, Canada. We investigated 371 boreal vascular plant communities varying 0 – 100% in proportion of human land use.

Results

Rank species occupancy curves revealed high species dominance regardless of disturbance: within any disturbance class a few species occupied nearly every site and most species were found in a low proportion of sites. However, species were more widespread and displayed more even occupancy in intermediately disturbed communities than among communities of either low or high disturbance. We defined specialists and generalists based on turnover in co-occupants and thereby assessed impacts of human disturbance on specialization of species and community homogenization. Generalists were not disproportionately found at higher disturbance sites, and did not occupy more sites. Communities with greater human disturbance were not more functionally homogeneous; they did not harbor communities with more generalists.

Conclusions

We unexpectedly did not observe strong linkages between species specialism/generalism and disturbance, nor between community homogenization and disturbance. These results contrast previous findings in more species rich, complex or spatially heterogeneous systems and ecological models. We suggest that broad occupancy-based intercommunity patterns are insensitive to human land use extent in boreal vascular plants, perhaps because of ubiquity of generalists, low species richness, and history of natural disturbance. The poor sensitivity of these metrics to disturbance presents challenges for monitoring and managing impacts to biodiversity in this region.  相似文献   

High proportion of diploid hybrids produced by interspecific diploid × tetraploid <Emphasis Type="Italic">Sorghum</Emphasis> hybridization     

Stan Cox  Pheonah Nabukalu  Andrew H. Paterson  Wenqian Kong  Susan Auckland  Lisa Rainville  Sheila Cox  Shuwen Wang 《Genetic Resources and Crop Evolution》2018,65(2):387-390

A perennial version of grain sorghum [S. bicolor (L.) Moench] would create opportunities for greatly reducing tillage and preventing soil degradation. Efforts to select for perenniality and grain production among progeny of hybrids between S. bicolor (2n = 20) and the weedy tetraploid perennial S. halepense (L.) Pers. (2n = 40) are complicated in that F₁ hybrids produced by diploid × tetraploid sorghum crosses are usually tetraploid. In 2013, a set of random pollinations between 19 diploid cytoplasmic male-sterile inbred lines and 43 tetraploid perennial plants produced 165 F₁ hybrid plants, more than 75% of which had highly atypical plant, panicle, and seed phenotypes. Phenotypic segregation in F₂ populations derived from atypical hybrids was also anomalous. Examination of mitotic metaphase cells in F₁ or F₂ root tips revealed that 129 of the 165 hybrids were diploid. Parentage of the diploid progenies was confirmed using simple-sequence repeat analysis. The mechanism by which diploid hybrids arise from diploid × tetraploid crosses is unknown, but it may involve either production of monohaploid (n = 10) pollen by the tetraploid parent or chromosome elimination during early cell divisions following formation of the triploid zygote. The ability to produce diploid germplasm segregating for S. bicolor and S. halepense alleles could have great utility, both for the development of perennial sorghum and for the improvement of conventional grain sorghum.  相似文献   

Chromosome analysis of ducklings with a defective phenotype     

S Lemáková  M Sitko 《Veterinární medicína》1987,32(5):315-320

In two equal periods, using the conventional method of processing bone-marrow cells after Konstantinov and Dobriyanov (1974), we studied the connection between the occurrence of chromosomal aberrations and deviations of phenotype. In the first part of the observation we found 8.5% numerical aberrations in 20 ducklings with retarded motility, torticollis and contractures of the fingers, compared with 1.27% in the control group with normal phenotype. In the second part of the observation the occurrence of aberrations in ducklings with defective phenotype of the same breeding dropped considerably to 1.7% and in the control group to 0.54%. The statistical evaluation of the results showed statistically significant differences (chi (4)2 = 56.78; p less than 0.05, and/or chi (4)2 = 27.74; p less than 0.05).  相似文献   

Typing and number of chromosomes in the common pheasant and rock partridge     

S Lemáková 《Veterinární medicína》1984,29(2):107-111

The typology and number of chromosomes were studied in two species of feathered game: common pheasant and rock partridge. The use of the traditional method of bone marrow processing after Konstantinov and Dobriyanov (1974) made it possible in the studied species to form the caryotypes, even despite the problems encountered in avian cytogenetics. Chromosome typology was possible only in the largest chromosomes. In the remaining microchromosomes the position of centromere was not determined and the microchromosomes themselves appeared as points arranged by size in caryotypes. The number of chromosomes in common pheasant and rock partridge was 80.  相似文献