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排序方式: 共有388条查询结果,搜索用时 15 毫秒
1.
Jeff A Johnson Heather RL Lerner Pamela C Rasmussen David P Mindell 《BMC evolutionary biology》2006,6(1):65-12
Background
Populations of the Oriental White-backed Vulture (Gyps bengalensis) have declined by over 95% within the past decade. This decline is largely due to incidental consumption of the non-steroidal anti-inflammatory veterinary pharmaceutical diclofenac, commonly used to treat domestic livestock. The conservation status of other Gyps vultures in southern Asia is also of immediate concern, given the lack of knowledge regarding status of their populations and the continuing existence of taxonomic uncertainties. In this study, we assess phylogenetic relationships for all recognized species and the majority of subspecies within the genus Gyps. The continuing veterinary use of diclofenac is an unknown but potential risk to related species with similar feeding habits to Gyps bengalensis. Therefore, an accurate assessment of the phylogenetic relationships among Gyps vultures should aid in their conservation by clarifying taxonomic uncertainties, and enabling inference of their respective relatedness to susceptible G. bengalensis. 相似文献2.
3.
Action of hydroxyethyl starch on the flow properties of human erythrocyte suspensions 总被引:1,自引:0,他引:1
Hydroxyethyl starch (HES) has often been used as a plasma expander, but questions still remain concerning the mechanisms by which it produces changes in the rheological properties of blood and erythrocyte (RBC) suspensions under various flow conditions. The present investigation has shown that the dynamic viscosity of HES (232,000 and 565,000 daltons) solutions rises in a nonlinear fashion with increasing HES concentration, and for a given concentration of HES exhibits Newtonian behavior at shear rates between 0.15 to 124 sec-1. At low (less than 0.9 sec-1) shear rates the apparent viscosity of a 40% RBC suspension increases with lower concentrations of HES because of RBC aggregation. At higher concentrations of HES, increases in suspension viscosity are due to an increase in the viscosity of the continuous phase since the RBC are largely disaggregated. At high (greater than 36 sec-1) shear rates the relative viscosity (eta/eta O) of RBC suspensions slowly decreases with increasing HES concentration. At low shear rates eta/eta O increases and then decreases with increasing HES concentration. Evidence of the concentration-dependent effects of HES on RBC aggregation is provided not only by the viscometric analysis but also from measurements of erythrocyte sedimentation rate (ESR) and the zeta sedimentation ratio (ZSR). HES is a more potent aggregating agent in phosphate buffered saline (PBS) than it is in plasma. Polymer size has only a slight effect on the extent of RBC aggregation produced, but does have a significant effect on the concentration of polymer at which maximum aggregation occurs. The viscosity-corrected electrophoretic mobility of RBC in HES rises monotonically with the concentration of HES in the suspending medium. Decreases in the extent of RBC aggregation with increasing polymer concentrations probably result from an increase in the electrostatic repulsive forces between the cells. 相似文献
4.
Human natural killer cell activity is reversibly inhibited by antagonists of lipoxygenation 总被引:3,自引:0,他引:3
W E Seaman 《Journal of immunology (Baltimore, Md. : 1950)》1983,131(6):2953-2957
We here demonstrate that NK cell activity by human peripheral blood mononuclear cells (PBMC) against K562 or MOLT-4 target cells is rapidly and reversibly inhibited by two agents that inhibit the lipoxygenation of fatty acids, BW755C and nordihydroguaiaretic acid (NDGA). Natural killing by nonadherent PBMC was similarly inhibited by both agents, indicating that monocytes were not required for the effect. The inhibition of natural killing was not seen with indomethacin at concentrations that inhibit prostaglandin synthesis but not the lipoxygenation of arachidonic acid. Moreover, indomethacin did not alter inhibition by either BW755C or NDGA. Thus, suppression of natural killing by these agents was not mediated by the effects on prostaglandin synthesis; neither agent inhibited target cell binding. These results suggest that products of lipoxygenation are required for target cell lysis by human NK cells. 相似文献
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7.
alpha 1-Proteinase inhibitor (alpha 1-PI), a member of the serine
proteinase inhibitor superfamily, has a primary role in controlling
neutrophil elastase activity within the mammalian circulation. Several
studies have indicated that the reactive center region of alpha 1-PI, the
amino acid sequence of which is critical to recognition of and binding to
target proteinases, is highly divergent within and among species. This
appears to be a consequence of accelerated rates of evolution that may have
been driven by positive Darwinian selection. In order to examine this and
other features of alpha 1-PI evolution in more detail, we have isolated and
sequenced cDNAs representing alpha 1- PI mRNAs of the mouse species Mus
saxicola and Mus minutoides and have compared these with a number of other
mammalian alpha 1-PI mRNAs. Relative to other mammalian mRNAs, the extent
of nonsynonymous substitution is generally high throughout the alpha 1-PI
mRNA molecule, indicating greater overall rates of amino acid substitution.
Within and among mouse species, the 5'-half of the mRNA, but not the
3'-half, has been homogenized by concerted evolution. Finally, the reactive
center is under diversifying or positive Darwinian selection in murid
rodents (rats, mice) and guinea pigs yet is under purifying selection in
primates and artiodactyls. The significance of these findings to alpha 1-PI
function and the possible selective forces driving evolution of serpins in
general are discussed.
相似文献
8.
When distributional assumptions for analysis of variance are suspect, and nonparametric methods are unavailable, ecologists frequently employ rank transformation (RT) methods. The technique replaces observations by their ranks, which are then analysed using standard parametric tests. RT methods are widely recommended in statistics texts and in manuals for packages like SAS and IMSL. They are robust and powerful for the analysis of additive factorial designs. Recently, however, RT methods have been found to be grossly inappropriate for use with non-additive models. This severe limitation remains largely unreported outside of the theoretical statistics literature. Our goal is to explain this shortcoming of RT methods. 相似文献
9.
Polystoma marmorati n. sp. is described as a new polystomatid species parasitic in the urinary bladder of the painted reed frog Hyperolius marmoratus marmoratus collected in southern Natal, South Africa. Parasite prevalence varied from 14.5 to 47.4% and the mean intensity from 1.0 to 1.1. The hamuli of the new species have a characteristic, partly fragmented appearance, a feature also seen in Polystoma batchvarivi, the only other polystome described from a species of the genus Hyperolius. The similarity between the two species, in spite of their geographical separation, is commented upon. 相似文献
10.
Mitochondrial DNA polymorphisms in subterranean mole-rats of the Spalax ehrenbergi superspecies in Israel, and its peripheral isolates 总被引:1,自引:0,他引:1
Nevo E; Honeycutt RL; Yonekawa H; Nelson K; Hanzawa N 《Molecular biology and evolution》1993,10(3):590-604
Patterns of mitochondrial DNA (mtDNA) variation were examined in 133
mole-rats constituting all four chromosomal species (2n = 52, 2n = 54, 2n =
58, and 2n = 60) of the Spalax ehrenbergi superspecies in Israel, as well
as the peripheral isolates of 2n = 60. In the main range of the complex, a
total of 28 mtDNA haplotypes were found in 64 mole-rats, with most
haplotypes being unique to either a single chromosomal species or
population. mtDNA divergence increased from low to high diploid number in a
north-to-south direction in Israel. Overall levels of mtDNA diversity were
unexpectedly the highest in the 2n = 60, the youngest species of the
complex. The mtDNA haplotypes can be separated into two major groups, 2n =
52-54 and 2n = 58-60, and a phylogenetic analysis for each group revealed
evidence of a few haplotypes not sorted by diploid number. The overall
patterns of mtDNA divergence seen within and among the four chromosomal
species are consistent with the parapatric mode of speciation as suggested
from previous studies of allozyme and DNA hybridization. In a separate data
set the patterns of mtDNA variation were examined across the main
geographic range and across peripheral semi-isolates and isolates of the 2n
= 60 chromosomal species. Fifteen haplotypes were found in 69 mole-rats.
High levels of mtDNA diversity characterized the main range, semi-isolated,
and even some desert isolated populations. The peripheral isolates contain
much mtDNA diversity, including novel haplotypes.
相似文献