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121.
122.
The population structure of Ascochyta rabiei (teleomorph: Didymella rabiei ) in Tunisia was estimated among five populations sampled from the main chickpea growing regions using simple sequence repeat markers (SSR) and a mating type ( MAT ) marker. Mating type 2 isolates ( MAT1-2 ) had reduced genetic and genotypic diversity relative to mating type 1 isolates ( MAT1-1 ). This result, coupled with previous observations of lower overall frequency and restricted geographical distribution of MAT1-2 in Tunisia, and recent (2001) observation of the sexual stage, support the hypothesis of a recent introduction of MAT1-2 . Despite the presence of both mating types in Nabeul, Kef and Jendouba, the hypothesis of random mating was rejected in these locations with multilocus gametic disequilibrium tests. Highly significant genetic differentiation ( θ = 0·32, G ST = 0·28, P < 0·001) was detected among populations and genetic distance and cluster analyses based on pooled allele frequencies revealed that populations from Nabeul and Kef were distinct from those in Beja, Bizerte and Jendouba. More than 70% of total gene diversity ( H T = 0·55) detected was attributable to variation within populations compared to 28% among populations. This result, coupled with the occurrence of private alleles in each population, suggests that gene flow is currently limited among populations, even those separated by short geographic distances. The presence of two main genetic clusters was confirmed using Bayesian model-based population structure analyses of multilocus genotypes (MLGs) without regard to geographic origin of samples. The presence of MAT1-2 isolates in both clusters suggests at least two independent introductions of MAT1-2 into Tunisia that are likely to be the result of importation and planting of infected chickpea seeds. 相似文献
123.
Testosterone serum profile,semen characteristics and testicular biometry of Mangalarga Marchador stallions in a tropical environment
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B Waddington JM Penitente‐Filho JGS Neves RO Pinho AY Chaya PP Maitan CO Silveira MG Neves SEF Guimarães GR de Carvalho JD Guimarães 《Reproduction in domestic animals》2017,52(2):335-343
This study was conducted to characterize the daily profile of testosterone secretion and its mean concentrations in the four seasons as well as to evaluate the semen characteristics and testicular biometry of Mangalarga Marchador stallions throughout the year in a tropical region. Three stallions were submitted to semen collections and evaluation of testicular biometry every 14 days along a year. Blood samples were collected once at the middle of each season, in a 20‐min interval during 24 hr in order to evaluate the testosterone secretion profiles among seasons. Testosterone concentrations along the day were higher at the beginning of the afternoon (from 12:00 to 15:00 hr), but a circadian secretion was not clearly observed. Mean testosterone concentrations did not differ among seasons (p > .05), but a pattern of secretion along the day showed variations with higher concentrations in the afternoon during the winter. Ejaculate volume was higher during summer; however, sperm motility decreased in summer and spring. Total sperm in ejaculate, sperm morphology and testicular biometry kept constant along the year showing no differences among the seasons. The results demonstrated that in a tropical region, reproductive aspects of stallions did not show a clearly defined seasonal variation, and months of autumn and winter were not unsuitable for reproduction of the males. 相似文献
124.
Dinoflagellates are single-celled organisms that reflect the ecological conditions in modern oceans and lakes. Ultrastructural data and molecular phylogeny suggest that they originated in the Neoproterozoic, yet dinoflagellate ancestors are classified only to the Middle Triassic ( approximately 240 million years ago). Examination of dinoflagellate-specific biological markers (dinosteranes and 4alpha-methyl-24-ethylcholestane) in concentrated microfossils with known morphology identified ancient dinoflagellate ancestors from the Early Cambrian ( approximately 520 million years ago). 相似文献
125.
SL Collins AK Knapp JMB riggs JM Blair EM Steinauer 《Science (New York, N.Y.)》1998,280(5364):745-747
Species diversity has declined in ecosystems worldwide as a result of habitat fragmentation, eutrophication, and land-use change. If such decline is to be halted ecological mechanisms that restore or maintain biodiversity are needed. Two long-term field experiments were performed in native grassland to assess the effects of fire, nitrogen addition, and grazing or mowing on plant species diversity. In one experiment, richness declined on burned and fertilized treatments, whereas mowing maintained diversity under these conditions. In the second experiment, loss of species diversity due to frequent burning was reversed by bison, a keystone herbivore in North American grasslands. Thus, mowing or the reestablishment of grazing in anthropogenically stressed grasslands enhanced biodiversity. 相似文献
126.
The small eccentricity of Neptune may be a direct consequence of apsidal wave interaction with the trans-Neptune population of debris called the Kuiper belt. The Kuiper belt is subject to resonant perturbations from Neptune, so that the transport of angular momentum by density waves can result in orbital evolution of Neptune as well as changes in the structure of the Kuiper belt. In particular, for a belt eroded out to the vicinity of Neptune's 2:1 resonance at about 48 astronomical units, Neptune's eccentricity can damp to its current value over the age of the solar system if the belt contains slightly more than an earth mass of material out to about 75 astronomical units. 相似文献
127.
A cluster analysis of the stratigraphic distribution of all Ordovician trilobite families, based on a comprehensive taxonomic database, identified two major faunas with disjunct temporal diversity trends. The Ibex Fauna behaved as a cohort, declining through the Ordovician and disappearing at the end-Ordovician mass extinction. In contrast, the Whiterock Fauna radiated rapidly during the Middle Ordovician and gave rise to all post-Ordovician trilobite diversity. Its pattern of diversification matches that of the Paleozoic Evolutionary Fauna; hence, trilobites were active participants in the great Ordovician radiations. Extinction patterns at the end of the Ordovician are related to clade size: Surviving trilobite families show higher genus diversity than extinguished families. 相似文献
128.
Soulen Jr RJ JM Byers MS Osofsky B Nadgorny T Ambrose SF Cheng Broussard C T Tanaka PR J Nowak JS Moodera A Barry JMD Coey 《Science (New York, N.Y.)》1998,282(5386):85-88
A superconducting point contact is used to determine the spin polarization at the Fermi energy of several metals. Because the process of supercurrent conversion at a superconductor-metal interface (Andreev reflection) is limited by the minority spin population near the Fermi surface, the differential conductance of the point contact can reveal the spin polarization of the metal. This technique has been applied to a variety of metals where the spin polarization ranges from 35 to 90 percent: Ni0.8Fe0.2, Ni, Co, Fe, NiMnSb, La0.7Sr0.3MnO3, and CrO2. 相似文献
129.
K. Mc Entee DVM PhD dipl ECVIM-CA C. Clercx DVM PhD Dipl ECVIM-CA T. Flandre DVM E. Jonville DVM C. Pynnaert DVM R. Van Beneden MS JM Ketelslegers MD PhD C. Michaux DVM Phd M. Balligand DVM PhD dipl ECVS-CA N. Miserque DVM M. Henroteaux DVM 《Journal of Veterinary Cardiology》2000,2(2):7
The aims of this study were to investigate (1) hormonal activation before and during dobutamine cardiac stress testing (DST) in a canine model of early left ventricular dysfunction (ELVD) induced by rapid right ventricular pacing (RRVP) and (2) the relationship between this hormonal profile and carnitine concentrations.Before the pacing period, the 6 dogs were assigned to 2 groups according their baseline total plasma carnitine concentration. A DST was performed on each dog before activation of the pacemaker and every 3 to 4 days during development of 3 progressive stages of ELVD (stages 1, 2 and 3). Plasma atrial natriuretic factor (ANF), angiotensin II (ANG II) and endothelin-1 (ET-1) levels were measured at the start and at the end of each DST. Effects of ELVD, DST and plasma carnitine concentration on these measurements were tested.The RRVP induced a significant increase of ANF and ANG II and a non significant trend toward increase of ET-1 in all dogs.Before the pacing period, ANF remained constant during the DST in dogs with normal total plasma carnitine concentration, while it significantly decreased in dogs with low total plasma carnitine concentration. Dobutamine stress testing induced a significant decrease in ANF in all dogs in ELVD. Dobutamine infusion induced a significant increase in ANG II in all dogs before as well as during the pacing period while ET-1 was unchanged.These results suggest that investigation of the hormonal profile before and after a dobutamine challenge might provide important diagnostic information in dogs with asymptomatic or mildly symptomatic cardiac dysfunction of different origins. 相似文献
130.
R H Dyer G E Martin P C Buscemi 《Journal of the Association of Official Analytical Chemists》1976,59(3):675-677
Wine samples containing beta-asarone (cis-2,4,5-trimethoxy-l-propenylbenzene) are distilled; beta-asarone is extracted by hexane and then quantitatively determined by gas-liquid chromatography (GLC), using ethyl palmitate as the internal standard. The GLC procedure is rapid and yields precise and accurate results. Mass spectrometry confirmed the identity of the GLC peak as beta-asarone. The ultraviolet spectra of beta-asarone and its isomer were also determined. 相似文献