共查询到20条相似文献，搜索用时 31 毫秒
1.
Detailed analysis of evolutionary changes in a 10-million-year long Late Neogene lineage of planktonic foraminifera has revealed a pattern that is not consistent with either the gradualistic or the punctuational model of evolution. The lineage was in stasis over a considerable part of its total duration but underwent relatively rapid, but not geologically instantaneous, gradual morphologic change that did not lead to lineage splitting. The term punctuated gradualism is suggested for this evolutionary modality. 相似文献
2.
东亚是温带植物种丰度的热点地区,它与北美东部具有相似的气候和植物组成,但是物种丰度是北美东部的2倍。第四纪冰期和间冰期反复的气候变动形成了当今北半球温带物种的分布格局与遗传结构,反复的气候波动导致海平面的反复升降,为东亚地区物种扩张提供了路线,导致种群不断的分开和连接,从而促进了进化的发生和异域物种的形成。介绍了森林树种的群体遗传学研究及分子系统地理学研究情况,阐述了东亚地区森林树种迁移扩散研究概况,包括物种迁移扩散模式及森林树种天然种群在东亚的迁移扩散情况,最后展望了该研究领域的发展趋势。 相似文献
3.
目的 探讨冠心病心血瘀阻证动态演变过程中血瘀证前期、亚血瘀证期、心血瘀阻证期3个阶段的代谢组学通路。方法 信号通路分析采用KEGG,代谢产物分子注释、相关的酶或转运蛋白及其相关性质分析采用HMDB,代谢产物路径可视化采用metPA网络软件。结果 用MetPA分析的生物代谢通路显示,12个代谢产物参与了22条代谢路径。其中6条通路（氨酰-tRNA生物合成、缬氨酸,亮氨酸和异亮氨酸生物合成、缬氨酸,亮氨酸和异亮氨酸生物合成及降解、精氨酸和脯氨酸代谢、半乳糖代谢,D-精氨酸与D-鸟氨酸代谢）的影响值P<0.05。结论 6条密切相关的通路主要集中在亚血瘀证期和心血瘀阻期。 相似文献
4.
利用1961—2016年天长市光、热、水气候资源和一季稻的生育特点,分析气象因子对一季稻各生育期的影响,构建了天长一季稻气候适宜度模型,探讨气候变暖背景下一季稻气候适宜度演变特征。结果表明,天长一季稻生育期温度适宜度最大,日照适宜度次之,降水适宜度最小,即一季稻生育期光热资源充沛,降水量是主要的限制因子;从平均值来看,播种—三叶期、拔节—孕穗期及灌浆—成熟期气候适宜度较高,而移栽—返青期最低;1961—2016年天长一季稻全生育期气候适宜度略有减小趋势,气候适宜度年际波动大。 相似文献
5.
Vuilleumier BS 《Science (New York, N.Y.)》1971,173(3999):771-780
In recent years, the view that Pleistocene climatic events played a major role in the evolution of the biotas of southern, primarily tropical continents has begun to displace the previously held conviction that these areas remained relatively stable during the Quaternary. Studies of speciation patterns of high Andean plant and avian taxa (7-14) have led to the conclusion that Pleistocene climatic events were the factors that ultimately shaped the patterns now observed in the paramo-puna and the related Patagonian flora and fauna. The final uplift of the Andes at the end of the Tertiary automatically limits the age of the high Andean habitats and their biotas to the Quaternary. Within this period, the number of ecological fluctuations caused by the glaciations could easily have provided the mechanism behind the patterns now present in these habitats (Appendix, 1; Figs. 1 and 2; Table 1). In glacial periods, when vegetation belts, were lowered, organisms in the paramo-puna habitat were allowed to expand their ranges. In interglacial periods, these taxa were isolated on disjunct peaks, where differentiation could occur. At times of ice expansion, glacial tongues and lakes provided local barriers to gene exchange, whereas in warm, interglacial times, dry river valleys were a major deterrent to the interbreeding of populations on different mountains (Fig. 2; Table 2). A preliminary analysis of about 10 to 12 percent of the total South American avifauna (14), subsequent to the study of the high Andean biota, suggested that the birds of all the major habitats of the continent possess, with about equal frequency, similar stages of speciation. This correspondence in levels of evolution indicated that the avifauna of vegetation zones which were thought to have been more stable (for example, tropical rainforests) are as actively speciating as are those of the more recent paramo-puna habitats. More intensive work on lowland tropical taxa (16, 19-21) and recent work on montane forest elements (40) now justify the conclusion that the floras and faunas of these areas were also greatly affected by Pleistocene climatic shifts. In the broad region of South America that lies within the tropics, a series of humid-arid cycles (Appendix, 6, 8-10) drastically and repeatedly altered vegetation patterns during the Quaternary. Both montane and lowland rainforests were fragmented during dry periods and were able to reexpand during humid phases. Speciation of forest elements was initiated-and sometimes completed-in isolated patches of the fragmented forest. Secondary contact, with hybridization or reunition of populations that did not become reproductively isolated, occurred in periods of reexpansion. These biological data, combined with supportive geological evidence (Appendix, 1-11), show that climatic events during the last million or so years have affected the biota of South America as much as the Pleistocene glacial changes affected the biotas of Eurasia and North America. Since most of South America lies within tropical latitudes, it is suggested here that part of the diversity of species in the tropical areas of this continent is due to two historical factors: the lack of wholesale elimination of species (compared with northern and high latitudes), and ample opportunity for speciation in successive periods of ecological isolation. The apparent paradox of the wealth of species in the "stable tropics" is partially explained by the fact that the tropics have probably been quite unstable, from the point of view of their biotas, during the Pleistocene and perhaps part of the Tertiary. 相似文献
6.
Human influenza A (subtype H3N2) is characterized genetically by the limited standing diversity of its hemagglutinin and antigenically by clusters that emerge and replace each other within 2 to 8 years. By introducing an epidemiological model that allows for differences between the genetic and antigenic properties of the virus's hemagglutinin, we show that these patterns can arise from cluster-specific immunity alone. Central to the formulation is a genotype-to-phenotype mapping, based on neutral networks, with antigenic phenotypes, not genotypes, determining the degree of strain cross-immunity. The model parsimoniously explains well-known, as well as previously unremarked, features of interpandemic influenza dynamics and evolution. It captures the observed boom-and-bust pattern of viral evolution, with periods of antigenic stasis during which genetic diversity grows, and with episodic contraction of this diversity during cluster transitions. 相似文献
7.
8.
[目的]通过对光合生理指标和形态学指标的对比,探讨黄山松和马尾松对不同海拔的适应性。[方法]选取黄山风景区365、882m 2个海拔的马尾松群落和882、1 575 2个海拔的黄山松群落为研究对象,分别测定其针叶长、叶面积、单根叶重以及比叶面积等形态指标和光合速率、蒸腾速率、气孔导度、胞间CO2浓度等光合生理指标。用Duncan多重比较方法,检验了种内和种间差异。物种的参数测定使用LI-6400便携式光合测定仪等工具,数据整理和分析使用Spss18.0和Excel等软件。[结果]同一物种在不同海拔各形态指数差异性在0.05水平显著;同一海拔的不同物种形态指数差异性不显著(P0.05);光合生理参数在种内和种间差异性均不显著(P0.05)。[结论]在长期的进化过程中,黄山松和马尾松通过表现型的改变维持了其生理生态的稳定性,很好地适应了当地高山严酷的环境,即二者均对山地具有较强的适应能力。 相似文献
9.
10.
11.
Simulation of changes in energy costs of soil formation during the period of irrigation reclamation in the steppe zone has been performed using Wavelets analysis. A method has been proposed for the evaluation of natural-anthropogenic soil-forming process with consideration for the contribution of irrigation water to the hydrothermal regime during the growing season and the prediction of soil evolution under the effect of changing climatic conditions for the area of irrigated agriculture. 相似文献
12.
六盘山植被覆盖度的变化及其与气温降水蒸发量的关系 总被引：1，自引：0，他引：1
使用1982～2005年的NDVI资料和气象观测资料,将NDVI资料换算成覆盖度,分析六盘山植被覆盖度的变化情况及其与温度、降水和蒸发量的关系。结果表明,六盘山的植被覆盖度一直处于波动状态,这种波动主要是由于气候原因引起的;植被覆盖度增加或减少的季节性的明显差异,与天然草原植被恢复和退耕还林草工程有关;降水对六盘山北部各季节的植被生长影响很大,对中部则只是在春季影响较大,在南部降水已不是影响植被生长的限制因素;气温的变化对六盘山北部植被生长影响很小,对中、南部春季和夏季植被的生长影响较大,其中春季为正相关,而夏季则为负相关;蒸发量对六盘山各区域覆盖度的影响较为一致,春、夏季蒸发量与夏季植被覆盖度呈负相关,而冬季蒸发量与冬季植被覆盖度呈显著的正相关。 相似文献
13.
苏南茶区无霜期气候变化趋势研究 总被引：3，自引：0，他引：3
利用江苏省苏南茶区内9个站点1961-2008年的气象观测资料,采用气候倾向率、Mann-Kendall(简称M-K法)等数理统计方法分析了无霜期的气候变化,以期为苏南茶区调整茶树种植结构提供依据。结果表明:苏南茶区无霜期呈显著延长的变化趋势,平均每10a延长7～9d(苏锡常区域);极短无霜期和偏短无霜期均出现在1996年之前;极长无霜期和偏长无霜期均出现在1989年之后;各区无霜期均发生气候突变,宁镇区域和苏锡常区域气候突变点分别为1996年和1984年,突变后平均无霜期分别延长了16、15d。因此,建议苏南茶区茶树品种的种植结构应随气候变化进行调整,宁镇区域和苏锡常区域北部要大力引进早芽种,适度引进特早芽种;苏锡常区域南部适宜大力引进和推广特早芽种。 相似文献
14.
15.
Nagalingum NS Marshall CR Quental TB Rai HS Little DP Mathews S 《Science (New York, N.Y.)》2011,334(6057):796-799
Modern survivors of previously more diverse lineages are regarded as living fossils, particularly when characterized by morphological stasis. Cycads are often cited as a classic example, reaching their greatest diversity during the Jurassic-Cretaceous (199.6 to 65.5 million years ago) then dwindling to their present diversity of ~300 species as flowering plants rose to dominance. Using fossil-calibrated molecular phylogenies, we show that cycads underwent a near synchronous global rediversification beginning in the late Miocene, followed by a slowdown toward the Recent. Although the cycad lineage is ancient, our timetrees indicate that living cycad species are not much older than ~12 million years. These data reject the hypothesized role of dinosaurs in generating extant diversity and the designation of today's cycad species as living fossils. 相似文献
16.
Farci P Shimoda A Coiana A Diaz G Peddis G Melpolder JC Strazzera A Chien DY Munoz SJ Balestrieri A Purcell RH Alter HJ 《Science (New York, N.Y.)》2000,288(5464):339-344
The mechanisms by which hepatitis C virus (HCV) induces chronic infection in the vast majority of infected individuals are unknown. Sequences within the HCV E1 and E2 envelope genes were analyzed during the acute phase of hepatitis C in 12 patients with different clinical outcomes. Acute resolving hepatitis was associated with relative evolutionary stasis of the heterogeneous viral population (quasispecies), whereas progressing hepatitis correlated with genetic evolution of HCV. Consistent with the hypothesis of selective pressure by the host immune system, the sequence changes occurred almost exclusively within the hypervariable region 1 of the E2 gene and were temporally correlated with antibody seroconversion. These data indicate that the evolutionary dynamics of the HCV quasispecies during the acute phase of hepatitis C predict whether the infection will resolve or become chronic. 相似文献
17.
普达措国家公园海拔上限3个针叶树种径向生长对气候变化的响应 总被引：1，自引：1，他引：0
本文利用树木年轮学方法研究普达措国家公园海拔上限麦吊云杉、大果红杉和长苞冷杉的生长特征,构建差值年表并分析其与气候因子的关系,以揭示影响该区域3个主要树种径向生长的气候因子及对气候变化响应的种间差异。结果表明:1)生长后期的气候因子对该地区树木生长起着重要作用,但不同树种的响应方式存在差异;2)麦吊云杉生长主要受限于生长季的气候条件,与上年生长后期(上年9—10月)平均温度呈显著负相关,且当年生长盛期(6—8月)温度的升高有利于其径向生长;3)大果红杉生长主要受限于生长后期的水分条件,主要表现为与上年10月以及上年生长后期(9—10月)降水呈显著负相关;4)长苞冷杉生长主要受限于生长季的气候条件,主要表现为对当年生长季盛期(6—8月)以及当年生长季后期(9—10月)平均温度的显著正相关。本研究为香格里拉地区的气候重建提供基础数据。 相似文献
18.
How can species remain unaltered for long periods yet also undergo rapid diversification? By linking genetic variation to phenotypic variation via environmental stress, the Hsp90 protein-folding reservoir might promote both stasis and change. However, the nature and adaptive value of Hsp90-contingent traits remain uncertain. In ecologically and genetically diverse yeasts, we find such traits to be both common and frequently adaptive. Most are based on preexisting variation, with causative polymorphisms occurring in coding and regulatory sequences alike. A common temperature stress alters phenotypes similarly. Both selective inhibition of Hsp90 and temperature stress increase correlations between genotype and phenotype. This system broadly determines the adaptive value of standing genetic variation and, in so doing, has influenced the evolution of current genomes. 相似文献
19.
Rapid changes in flowering time in British plants 总被引：4，自引：0，他引：4
The average first flowering date of 385 British plant species has advanced by 4.5 days during the past decade compared with the previous four decades: 16% of species flowered significantly earlier in the 1990s than previously, with an average advancement of 15 days in a decade. Ten species (3%) flowered significantly later in the 1990s than previously. These data reveal the strongest biological signal yet of climatic change. Flowering is especially sensitive to the temperature in the previous month, and spring-flowering species are most responsive. However, large interspecific differences in this response will affect both the structure of plant communities and gene flow between species as climate warms. Annuals are more likely to flower early than congeneric perennials, and insect-pollinated species more than wind-pollinated ones. 相似文献
20.
Cole K 《Science (New York, N.Y.)》1982,217(4565):1142-1145
Fossil assemblages from 53 packrat middens indicate which plant species were dominant during the last 24,000 years in the eastern Grand Canyon. Past vegetational patterns show associations that cannot be attributed to simple elevational displacement of the modern zones. A model emphasizing a latitudinal shift of climatic values is proposed. 相似文献