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长掌义县龙(Yixianosaurus longimanus)是发现于中国辽西下白垩统的一种小型兽脚类恐龙。最初的研究认为它代表一种进步的手盗龙类,但最近的一项研究工作质疑了这一系统发育假说,新的系统发育研究认为长掌义县龙代表一种原始的手盗龙类。鉴于长掌义县龙的系统位置会影响我们对兽脚类前肢和羽毛演化等关键问题的理解,因此需要评估哪一个系统发育假说更为可靠。本文评述了长掌义县龙所有可被用于系统发育研究的形态学特征,证明了这一小型兽脚类恐龙属于基干副鸟类,并很可能属于基干恐爪龙类。这一结论与最初的研究结果相吻合。这一系统位置也与长掌义县龙可能具片状羽毛相吻合,并且否定了手盗龙类前肢演化历史复杂的假说。 相似文献
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综述了近年来分子生物学标记技术在鲸类系统学研究中的进展。分子生物学证据支持鲸目与有蹄类之间有较近的亲缘关系,并支持鲸类的单系起源,但鲸类不同类群(须鲸类、抹香鲸类及不包括抹香鲸类的齿鲸类)之间的系统发生关系仍存在争议。抹香鲸类到底与须鲸类还是与其它齿鲸类有更近的亲缘关系,不同的分子生物学家所得到的结果并不一致。此外,分子生物学技术还被用于解决须鲸亚目和齿鲸亚目内科间以及科内种间的系统发生关系,特别是齿鲸亚目的海豚科、鼠豚科和淡水豚类。通过分子标记技术来研究鲸类种下的遗传结构是鲸类分子系统学研究中的一个新热点,使用的标记主要是mtDNA控制区、核DNA微卫星和主要组织相容性复合体(major histo-compatibilitv complex,MHC)等。 相似文献
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被子植物起源研究中几种观点的思考 总被引:1,自引:0,他引:1
对被子植物起源研究中的几种观点进行了讨论。(1)由于被子植物存在着一组共同的性状,它们不可能是从不同祖先起源的,而是有着共同的祖先。被子植物是一个单源起源的类群。现存被子植物分类系统是依据包括形态学(广义)、分子系统学、古植物学和植物地理学等的综合性状建立的,只能表示出现存类群的亲缘关系并且追溯到它们最近的祖先。人们现在还不可能建立一个包括全部已绝灭的类群和现代生存类群的谱系发生系统。因此,现存被子植物分类系统只能看作是“亲缘”系统。(2)分析了用于推测被子植物起源时间的分子、化石和地理分布证据。我们认为,要确定被子植物起源时间,植物化石是一类重要证据,但化石只能说是植物本身可保存部分和当时当地所提供的化石条件的综合反映,它们不可能就是植物类群或种的起源时间。人们还必须考虑到化石本身的演化历史。应用分子钟也是一种手段,但误差比较大。如果我们除了利用上述两种资料之外,根据植物类群的现代分布格局及其形成,把植物的演化同地球的历史和板块运动联系起来,以推断它们起源的时间,这无疑会增加其可信度。通过对56个种子植物不同演化水平的重要科属地理分布的研究结果,我们曾提出被子植物的起源时间可能要追溯到早侏罗世,甚至晚三叠世。(3)分析了基于分子证据所提出的被子植物基部类群——ANITA成员(包括无油樟科Amborellaceae、睡莲科Nymphaeaceae、八角目Illiciales、早落瓣科Trimeniaceae、木兰藤科Austrobaileyaceae)的性质,讨论了ANITA成员在现代几个被子植物分类系统中的系统位置的不同观点,评价了它们的形态学(广义)性状。指出ANITA的成员由于包含大量的祖征,是属于原始的类群。但由于它们的共有衍征很少,如花粉球形,说明它们在被子植物演化早期就分道扬镳了,沿着不同的传代线分化。因此ANITA是一个源于不同传代线的复合群。 相似文献
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不同生物类群包含的物种数目常存在巨大差异,这是生态学和生物学研究中普遍观察到的现象。然而,这一现象产生的原因仍然是未解之谜。从宏观进化的角度,进化时间假说和多样化速率假说是两个比较流行的假说。进化时间假说认为类群的演化时间越长,积累的物种丰富度越高;而多样化速率假说认为类群的净多样化速率越快,则其物种丰富度越高。为验证这两个假说,该文以一棵包含1 539个物种化石定年的虎耳草目系统发育树为基础,通过宏观进化分析获取了虎耳草目内15个科的物种形成和灭绝速率,并计算了每个科的平均多样化速率。结果表明:(1)虎耳草目的物种多样化速率有着增加的趋势,并且多样化速率的增加主要出现在温带和高山类群,如茶藨子科、景天科和芍药科等。(2)采用系统发育广义最小二乘模型(PGLS)和线性回归模型(LM)结果表明,虎耳草目15个科的物种丰富度与科的分化时间和科内物种的最近共同祖先年龄都没有显著相关关系,而与净多样化速率显著正相关(R2 =0.380,P<0.05)。该研究支持了多样化速率假说,认为不同科的净多样化速率的差异是导致虎耳草目科间物种数目差异的主要原因之一。全球气候变冷... 相似文献
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有瓣蝇类分类、系统发育及演化 总被引:1,自引:0,他引:1
有瓣蝇类(Calyptratae)隶属于昆虫纲(Insecta)四大超适应辐射类群之一的双翅目(Diptera),占双翅目已知物种多样性的近20%。有瓣蝇类分布广泛,生物学习性极为多样,在维系生态系统稳定中发挥着重要作用,是媒介、法医、传粉和天敌昆虫学研究领域的热点类群,也是探究双翅目系统演化及其成功适应辐射的关键类群。为了还原有瓣蝇类的演化历史,许多著名昆虫学者先后对该类昆虫开展过不同层面的研究。有瓣蝇类的单系性得到了普遍支持,并被分为3个总科——虱蝇总科(Hippoboscoidea)、蝇总科(Muscoidea)和狂蝇总科(Oestroidea),其中单系的狂蝇总科与多系的蝇总科聚为一支,再与虱蝇总科成为姐妹群。在科级阶元水平,蝠蝇科(Streblidae)(虱蝇总科)、花蝇科(Anthomyiidae)(蝇总科)、丽蝇科(Calliphoridae)(狂蝇总科)、邻寄蝇科(Rhinophoridae)(狂蝇总科)等类群的单系性仍有待验证,且新的科仍在不断被建立[如粉蝇科(Polleniidae)、乌鲁鲁蝇科(Ulurumyiidae)],因此,有瓣蝇类科级系统发育关系仍不十分明晰。已有研究对虱蝇总科虱蝇科(Hippoboscidae)、蝠蝇科、蛛蝇科(Nycteribiidae),蝇总科蝇科(Muscidae)、粪蝇科(Scathophagidae),狂蝇总科麻蝇科(Sarcophagidae)、狂蝇科(Oestridae)胃蝇亚科(Gasterophilinae)的演化历史进行研究,明确了起源与扩散、寄主转移、取食策略等关键生物学习性的演化历史。但由于部分关键类群生活史信息的缺失,以及尚未有效解决的系统发育关系,有瓣蝇类演化历史仍有许多待解之谜。本文综述了有瓣蝇类分类、系统发育及演化研究进展,是在系统学研究进入系统发育基因组学时代后对该类群相关研究进展的首次全面总结。 相似文献
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石松类和蕨类植物研究进展: 兼论国产类群的科级分类系统 总被引:8,自引:0,他引:8
综述了石松类和蕨类植物系统发育的最新研究成果。目前研究表明传统的蕨类植物概念(包括石松类和蕨类)需要修订, 一个关于蕨类植物的分类系统也已经发表。中国的植物多样性很丰富, 包括了世界上石松类和蕨类植物主要类群的代表。我们利用rbcL基因序列(包括国产蕨类63科中的62科179属184种)构建了系统发育树。基于rbcL序列分析所获得的石松类和蕨类各主要类群间的系统演化关系同以往对各个特定类群开展的较为密集的类群取样和多性状分析(形态学+分子序列证据)的结果基本一致。在参考Smith等人系统的基础上, 我们尝试性地对中国石松类和蕨类植物进行了科级水平上的系统发育重排。 相似文献
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《古脊椎动物学报》2015,(3)
报道和描述了一些在属级别上不确定的鸭嘴龙超科材料;标本发现于湖北省西北地区与河南交界的淅川盆地西南部的上白垩统马家村组中段。鸭嘴龙超科的骨骼化石和分散的恐龙蛋共存于同一层位,大部分的骨骼化石属于未离巢晚期和幼年早期的个体发育阶段。这一状况可以很好地解释为未离巢和幼年早期阶段的个体与更年老个体所组成的群体之间的地域分隔。通过直接的形态学对比研究,确信可以识别出至少两个鸭嘴龙超科的类群:其中一个类群可能代表了一个相对进步的基干鸭嘴龙类,而另一个类群则很可能归属于鸭嘴龙亚科。鉴于北美鸭嘴龙亚科最早出现的地层时代要更晚,中桑顿期马家村组中段的鸭嘴龙亚科化石材料提供了鸭嘴龙亚科乃至鸭嘴龙科亚洲起源的新证据。 相似文献
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Pushkar Shejwalkar 《Inorganica chimica acta》2011,366(1):209-218
New sulfur derivatives of phosphoramidite ligands were synthesized and the impact of the sulfur unit on the spectroscopic properties of their rhodium and iridium complexes was investigated. The new ligands Bn2NPSCH2CH2Sa(P-Sa) (Bn = benzyl, 4), Bn2NPSCHCHSa(CH2)3CaH2(P-Sa)(Ca-Sa) (6) and Bn2NP(4-XC6H4OMe)2 (X = S, 7a; X = O, 7b) were converted to the rhodium and iridium complexes trans-[Rh(CO)Cl(L)2] (L = 4, 6, 7), [RhCl(COD)(L)] (L = 4, 6, 7), [IrCl(COD)(7a)] and [IrCl2Cp∗(6)]. For comparison, some phosphoramidite complexes of these formulations also were synthesized. The new metal complexes were spectroscopically analyzed. For the carbonyl complexes, the νCO IR stretching frequencies were lower than for the corresponding phosphite and phosphoramidite ligands. The 1JPRh coupling constants for the rhodium complexes with the new ligands were also smaller than for the respective phosphoramidite and phosphite complexes. Finally, the 1JPSe coupling constants of the selenides of the new ligands were lower than those of the phosphoramidite ligands but higher than for PPh3. The spectroscopic data reveal that the new thio ligands 4, 6 and 7a are more electron donating than phosphites and phosphoramidites but less electron donating than PPh3. 相似文献
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Astrocytes transport the monocarboxylate acetate, but synaptosomes do not. The reason for this is unknown, because both preparations express monocarboxylate transporters (MCT). The transport and metabolism of lactate, another monocarboxylate, was examined in these two preparations, and the results were compared to those for acetate. Lactate transport is more rapid in astrocytes than in synaptosomes, but of lower affinity (Kms of 17 and 4 mM, respectively). Lactate (0.2 mM) is metabolized to CO2 more rapidly in synaptosomes than in astrocytes (rates of 0.37 and 0.07 nmol x mg protein(-1) x min(-1), respectively). The reason for this is unclear, but cellular differences in lactate dehydrogenase isotype expression may be involved. Acetate is metabolized to CO2 more rapidly in astrocytes than in synaptosomes (rates of 0.43 and 0.02 nmol x mg protein(-1) x min(-1), respectively). This is likely due to cellular differences in the expression of monocarboxylate transporter subtypes. 相似文献
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Hand JW 《Progress in biophysics and molecular biology》2007,93(1-3):192-194
The first and second sessions of the Workshop focussed on the basics of ultrasound and infrasound, their applications in both industry and medicine, and metrology and protection standards for ultrasound applications. 相似文献
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Gonzalez-Reimers E Rodriguez-Moreno F Martinez-Riera A Mas-Pascual A Delgado-Ureta E Galindo-Martin L Arnay-de la Rosa M Santolaria-Fernandez F 《Biological trace element research》1999,68(1):41-49
To elucidate accumulation of minerals in human iliac arteries with aging, the content of minerals was analyzed by inductively
coupled plasma atomic emission spectrometry. Bilateral common, internal, and external iliac arteries of 16 men and 8 women,
ranging ages from 65 to 93 yr, were examined. It was found that an extremely high accumulation of calcium and phosphorus occurred
in the common iliac artery at old age, being higher than that of the internal and external iliac arteries. It should be noted
that the accumulation of calcium and phosphorus is the highest in the common iliac artery among the human arteries examined
to date.
Regarding sexual differences, the content of calcium and phosphorus in the common and internal iliac arteries was higher in
women than in men, whereas their content in the external iliac artery was lower in women than in men. 相似文献
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J. Morley M.A. Bray R.W. Jones D.H. Nugteren D.A. van Dorp 《Prostaglandins & other lipid mediators》1979,17(5):729-736
The ability of partially purified human and guinea-pig haematogenous cell populations, when cultured in vitro, to metabolise arachidonic acid (AA) has been studied. Supernatants from 24 hour cell culture have been subjected to analysis for products of AA metabolism by gas chromatography with electron-capture detection.The cell types studied were human peripheral blood monocytes (both glass adherent and non-adherent), neutrophils, eosinophils and leukemic leucocytes; thoracic duct lymphocytes and lung alveolar macrophages. From the guinea-pig, induced and non-induced macrophage or neutrophil enriched peritoneal exudate populations, lymph node cells, peritoneal eosinophils and peripheral blood platelets were examined. Supernatants were assayed for the presence of PGE2, PGD2, PGF2α, TXB2 and 6-keto-PGF1α. In all types studied PGE2 and TXB2 were the major products formed. The identification of PGE2 and TXB2 was confirmed by GC/MS with multiple ion monitoring.The results have been compared with other reports and their possible significance discussed in relation to the proposed role of prostaglandins as mediators and modulators in immunopathology. 相似文献
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Allergic asthma can be precipitated by many factors. For the atopic person, fungus, pollen, dust mites, cockroach antigens, and diesel exhaust are all agents that may trigger an allergic attack. Cytokines and chemokines are integral mediators of fungal asthma. From the earliest time points, they recruit and activate the cells required for the clearance of fungus as well as being critical factors involved in the immunopathology of this disease. In the final analysis, it is clear that these mediators can act to the benefit or the detriment of the host. 相似文献
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Sandra M. Vaz 《Archives of biochemistry and biophysics》2009,484(2):127-431
In spite of the many studies on protein modifications by reactive species, knowledge about the products resulting from the oxidation of protein-aromatic residues, including protein-derived radicals and their stable products, remains limited. Here, we compared the oxidative modifications promoted by peroxynitrite and myeloperoxidase/hydrogen peroxide/nitrite in two model proteins, ribonuclease (6Tyr) and lysozyme (3Tyr/6Trp). The formation of protein-derived radicals and products was higher at pH 5.4 and 7.4 for myeloperoxidase and peroxynitrite, respectively. The main product was 3-nitro-Tyr for both proteins and oxidants. Lysozyme rendered similar yields of nitro-Trp, particularly when oxidized by peroxynitrite. Hydroxylated and dimerized products of Trp and Tyr were also produced, but in lower yields. Localization of the main modified residues indicates that peroxynitrite decomposes to radicals within the proteins behaving less specifically than myeloperoxidase. Nitrogen dioxide is emphasized as an important protein modifier. 相似文献