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排序方式: 共有300条查询结果,搜索用时 15 毫秒
1.
Multilocus clines between Müllerian mimetic races of Heliconius butterflies provide a classic example of the maintenance of hybrid zones and their importance in speciation. Concordant hybrid zones in the mimics Heliconius erato and H. melpomene in northern Peru were carefully documented in the 1980s, and this prior work now permits a historical analysis of the movement or stasis of the zones. Previous work predicted that these zones might be moving toward the Andes due to selective asymmetry. Extensive deforestation and climate change might also be expected to affect the positions and widths of the hybrid zones. We show that the positions and shapes of these hybrid zones have instead remained remarkably stable between 1985 and 2012. The stability of this interaction strongly implicates continued selection, rather than neutral mixing following secondary contact. The stability of cline widths and strong linkage disequilibria (gametic correlation coefficients Rmax = 0.35–0.56 among unlinked loci) over 25 years suggest that mimetic selection pressures on each color pattern locus have remained approximately constant (s ≈ 0.13–0.40 per locus in both species). Exceptionally high levels of precipitation at the edge of the easternmost Andes may act as a population density trough for butterflies, trapping the hybrid zones at the foot of the mountains, and preventing movement. As such, our results falsify one prediction of the Pleistocene Refugium theory: That the ranges of divergent species or subspecies should be centered on regions characterized by maxima of rainfall, with hybrid zones falling in more arid regions between them.  相似文献   
2.
目的分析某院解热镇痛抗炎药的临床应用情况,为临床合理用药提供参考。方法回顾性分析2015年1~12月某院解热镇痛抗炎药的销售金额、DDDs、DDDc、排名比等项目,并进行统计分析。结果某院不同品规的解热镇痛抗炎药31种,季度销售金额突破万元的药品有10种;DDDc≤1元的药品占总品种数的38.7%,1元DDDc10元的药品占比38.7%,DDDc≥10元的药品占22.6%。结论某院解热镇痛抗炎药品配备基本合理,优质药品在临床使用广泛,临床用药宜综合考虑药品的安全性、有效性、经济性。  相似文献   
3.
The application of polymorphic markers in construction of phylogenetic trees has been documented. Five polymorphic markers located in the PAH gene region including PAH-BglII, PAH-PvuII(A), PAH-EcoRI, PAH-MspI and PAH-STR were selected for analysis of phylogenetic relationships of the Iranians with 15 other populations of the world. The lowest genetic distance was observed between the Iranians and populations residing in Adygei (an ethnic group of the Russian Caucasus), Russia and Druze (a Middle Eastern group). However, East Asian populations including Han, Japanese and Cambodians, Khmer or the Oceanians (Melanesian, Nasioi) showed high genetic distance with the Iranians. The data suggested that the Iranians might have relatively close evolutionary history with the populations residing in Russia rather than East Asian populations. This study provided the first new molecular insight into the evolutionary history of the Iranian population.  相似文献   
4.
Constant-force isometric muscle training is useful for increasing the maximal strength , rehabilitation and work-fatigue assessment. Earlier studies have shown that muscle fatigue characteristics can be used for evaluating muscle endurance limit. Study Objective: To predict muscle endurance time during isometric task using frequency spectrum characteristics of surface electromyography signals along with analysis of frequency spectrum shape and scale during fatigue accumulation. Method: Thirteen subjects performed isometric lateral raise at 60% MVC of deltoid (lateral) till endurance limit. Time windowed sEMG frequency spectrum was modelled using 2-parameter distributions namely Gamma and Weibull for spectrum analysis and endurance prediction. Results: Gamma distribution provided better spectrum fitting (P < 0.001) than Weibull distribution. Spectrum Distribution demonstrated no change in shape but shifted towards lower frequency with increase of magnitude at characteristic mode frequency. Support Vector Regression based algorithm was developed for endurance time estimation using features derived from fitted frequency spectrum. Time taken till endurance limit for acquired dataset 38.53 ± 17.33 s (Mean ± Standard Deviation) was predicted with error of 0.029 ± 4.19 s . R-square: 0.956, training and test sets RMSE was calculated as 3.96 and 4.29 s respectively. The application of the algorithm suggested that model required 70% of sEMG signal from maximum time of endurance for high prediction accuracy. Conclusion: Endurance Limit prediction algorithm was developed for quantification of endurance time for optimizing isometric training and rehabilitation. Our method could help personalize and change conventional training method of same weight and duration for all subjects with optimized training parameters, based upon individual sEMG activity.  相似文献   
5.
目的:通过临床研究探讨电针治疗膝关节骨性关节炎的最佳参数,为临床提供更加规范性的治疗,进一步提高电针疗效。方法:将符合膝关节骨性关节炎诊断标准的73例单膝患者随机分为电针疏波组、密波组两组,均针刺患侧膝眼穴,疏波组接2Hz连续波治疗,密波组接40Hz连续波治疗,采用WOMAC评分对两组治疗后疼痛、僵硬、躯体功能进行评估,同时判断1个疗程及3个疗程治疗效果。结果:经统计学处理,完成第一疗程后,两组疼痛评分比较,P均<0.01,说明两组在疼痛疗效上存在差异。而两组僵硬和躯体功能评分的比较,P>0.05,显示两组没有统计学意义。第3疗程后,两组WOMAC总分比较,P均<0.01,具有极显著性差异,第3疗程症状积分低于第1疗程,说明第3疗程后症状改善优于第1疗程。结论:电针疏波组在改善疼痛上优于密波组;第3疗程后,总体症状改善情况优于第1疗程。  相似文献   
6.
Many quantitative genetic and adaptive dynamic models suggest that disruptive selection can maintain genetic polymorphism and be the driving force causing evolutionary divergence. These models also suggest that disruptive selection arises from frequency-dependent intraspecific competition. For convenience or historical precedence, these models assume that carrying capacity and competition functions follow a Gaussian distribution. Here, we propose a new analytical framework that relaxes the assumption of Gaussian competition and carrying capacity functions, and investigate how alternative shapes affect the likelihood of disruptive selection. We found that the shape of both carrying capacity and competition kernels interact to determine the likelihood of disruptive selection. For certain regions of the parametric space disruptive selection is facilitated, whereas for others it becomes more difficult. Our results suggest that the relationship between the degree of frequency dependence and the likelihood of disruptive selection is more complex than previously thought, depending on how resources are distributed and competition interference takes place. It is now important to describe the empirical patterns of resource distribution and competition in nature as a way to determine the likelihood of disruptive selection in natural populations.  相似文献   
7.
8.
Selection is frequency dependent when an individual's fitness depends on the frequency of its phenotype. Frequency‐dependent selection should be common in gynodioecious plants, where individuals are female or hermaphroditic; if the fitness of females is limited by the availability of pollen to fertilize their ovules, then they should have higher fitness when rare than when common. To test whether the fitness of females is frequency dependent, we manipulated the sex ratio in arrays of gynodioecious Lobelia siphilitica. To test whether fitness was frequency dependent because of variation in pollen availability, we compared open‐pollinated and supplemental hand‐pollinated plants. Open‐pollinated females produced more seeds when they were rare than when they were common, as expected if fitness is negatively frequency dependent. However, hand‐pollinated females also produced more seeds when they were rare, indicating that variation in pollen availability was not the cause of frequency‐dependent fitness. Instead, fitness was frequency dependent because both hand‐ and open‐pollinated females opened more flowers when they were rare than when they were common. This plasticity in the rate of anthesis could cause fitness to be frequency dependent even when reproduction is not pollen limited, and thus expand the conditions under which frequency‐dependent selection operates in gynodioecious species.  相似文献   
9.
In ascomycetes vegetative incompatibility can prevent the somatic exchange of genetic material between conspecifics. It must occur frequently in natural populations, since in all species studied many vegetative compatibility groups (VCGs) are found. Using a population-genetic approach, this paper explores two possible selective explanations for the evolution of vegetative incompatibility in asexual fungi: selection by a nuclear parasitic gene, and selection by a harmful cytoplasmic element. In a deterministic model, assuming a random spatial distribution of VCGs in an infinitely sized population, it is found that neither of these forms of frequency-dependent selection can explain the large number of VCGs found in nature. The selective pressure for more VCGs disappears once a limited number of VCGs exist, because the frequency of compatible interactions decreases when the number of VCGs increases. In comparing the two selective explanations, selection by a cytoplasmic element seems a more plausible explanation than selection by a nuclear gene.  相似文献   
10.
Human airway cilia contain soluble adenylyl cyclase (sAC) that produces cAMP upon HCO3/CO2 stimulation to increase ciliary beat frequency (CBF). Because apical HCO3 exchange depends on cystic fibrosis transmembrane conductance regulator (CFTR), malfunctioning CFTR might impair sAC-mediated CBF regulation in cells from patients with cystic fibrosis (CF). By Western blot, sAC isoforms are equally expressed in normal and CF airway epithelial cells, but CBF decreased more in CF than normal cells upon increased apical HCO3/CO2 exposure in part because of greater intracellular acidification from unbalanced CO2 influx (estimated by 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) fluorescence). Importantly, ciliated cell-specific cAMP production (estimated by FRET fluorescence ratio changes of tagged cAMP-dependent protein kinase (PKA) subunits expressed under a ciliated cell-specific promoter) in response to increased apical HCO3/CO2 perfusion was higher in normal compared with CF cells. Inhibition of bicarbonate influx via CFTR (CFTRinh172) and inhibition of sAC (KH7) and PKA activation (H89) led to larger CBF declines in normal cells, now comparable with changes seen in CF cells. These inhibitors also reduced FRET changes in normal cells to the level of CF cells with the expected exception of H89, which does not prevent dissociation of the fluorescently tagged PKA subunits. Basolateral permeabilization and subsequent perfusion with HCO3/CO2 rescued CBF and FRET changes in CF cells to the level of normal cells. These results suggest that CBF regulation by sAC-produced cAMP could be impaired in CF, thereby possibly contributing to mucociliary dysfunction in this disease, at least during disease exacerbations when airway acidification is common.  相似文献   
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