鸟类起源揭密

当今人们对鸟类的认识,主要集中在对现生鸟类的种类、数量,以及生态习性的探索和了解上,而对于有关鸟类始祖和起源等问题,却每每受限于化石发现的不连续性以及人们对自然认知的有限性上。然而,追求未知世界的天性却常常激发人类探索的激情,特别是当一些珍贵的化石标本被发现后。近些年来,我国出土了的大量鸟类化石,在学术界可以说是继始祖鸟之后又一次震惊世界的发现。始祖鸟鲜为人知的事实如果说人类认识鸟类是从现生鸟开始,那么,谱写鸟类进化历史的关键一环就是发现了始祖鸟。因为在此之前,人们虽然知道鸟的一般特征,但却不能给鸟类下定义…     

140000000年前的鸟——三塔中国鸟

一般认为,现代鸟类起源于始祖鸟.始祖鸟的化石发现在德国巴伐利亚省的索伦霍芬(Solnhofen)地区,化石埋藏在大约一亿五千万年前的晚侏罗世的地层中.始祖鸟身上同时具有爬行动物和鸟类动物的特征.始祖鸟化石的发现,为人类研究鸟类起源,提供了极其重要的初始材料.但是,始祖鸟是如何进而发展成为现代鸟类的?由于缺乏足够的化石材料而成了悬而未决的自然之谜.因此自始祖鸟发现后一百多年来,对鸟类进化的研究步履维艰.     

哈利特角形虫宿主新纪录及两个地理株系的比较

[目的]研究哈利特角形虫(Ceratomyxa hallettae)在不同地理分布和宿主种类下的遗传分化.[方法]基于哈利特角形虫的形态学、18S rDNA的分子特征、系统发育、宿主、地理分布等特征对哈利特角形虫中国株系与澳大利亚株系间的遗传分化进行研究.[结果]褐蓝子鱼(Siganus fuscescens)为哈利特角形虫的新宿主;形态学分析显示哈利特角形虫两株系在形态量度上差异较小;分子特征分析显示两株系18S rDNA序列之间存在7个变异位点,且两者相似度为99.60％,遗传距离为0.003 8;系统发育分析表明,哈利特角形虫中国株系聚于海洋角形虫进化支,且与澳大利亚株系形成姐妹群关系.[结论]宿主种类差异与长期的地理隔离可能是造成哈利特角形虫中国株系与澳大利亚株系在分子(18S rDNA)和形态上发生分化的主要原因.综合角形虫的系统发育、地理分布、宿主类群等信息可知,哈利特角形虫的原始宿主可能为单斑裸颊鲷(Lethrinus harak),而褐蓝子鱼应为该寄生虫经历了宿主转移事件而获得的新宿主.     

叩问恐龙蛋——鸟类与恐龙有怎样的亲缘关系?

鸟类的起源问题是生物学研究的热点领域,涉及鸟类的形态结构、飞行和羽毛等多方面内容。随着越来越多重要化石的发现,鸟类的恐龙起源学说已经逐渐为学术界所接受。特别是近年来,在我国早白垩世热河生物群以及侏罗纪地层中发现了许多保存精美的带毛恐龙、中生代鸟类化石等,     

基于RLCKVⅡ基因序列的蜘蛛抱蛋属系统发育分析

蜘蛛抱蛋属(Aspidistra Ker-Gawl.)是单子叶植物中同一属内物种多样性最为丰富的类群之一.由于缺乏分子序列方面的研究资料,该属种间系统发育关系一直都不清楚.本研究对20种具有代表性的蜘蛛抱蛋属植物的RLCKVⅡ基因进行了测序分析.结果表明,采用分子系统学证据所构建的该属系统发育关系不支持先前基于形态证据所建立的分类系统;蜘蛛抱蛋属植物复杂的平行进化关系很可能是该属分化早期频繁种间杂交的结果.RLCKVⅡ基因适用于禾本科、棕榈科和天门冬科等类群,可作为研究单子叶植物系统发育关系的备选基因.     

鸟类进化中的模糊问题初探

鸟类进化是生物进化的重要组成部分之一,是生物进化论、鸟类学研究的重要内容之一。根据古生物学研究成就,就古亚纲、今鸟亚纲进化、水鸟类形态结构进化中的模糊问题进行了初步探讨。     

陆生植物的起源和维管植物的早期演化

陆生植物的起源和演化是地球生命中的重大事件,它影响到地球上所有的其他生命和全球环境。在过去的20年中,从中奥陶世历经整个志留纪至早泥盆世的岩层中,化石植物(微化石和大化石)的新发现改变了人们对陆生植物起源的认识,并且为陆生植物和维管植物早期演化分异提供了基部类群分化的时间框架。据此人们识别出地史中的3个陆生植物的时代：始胚植物时代、始维管植物时代和真维管植物时代。另一方面,分子系统的研究使人们深入认识了植物的系统发育和早期分支。通过比较形态学研究和基因序列的共同努力,建立了植物系统发育树。总结了最近的进展和新的认识,评价了基于分支分析的系统发育研究。     

DNA测序在苔藓植物系统学研究中的应用

DNA序列分析技术是近年来兴起的研究植物系统发生的常用方法,由于其快速、高效、准确等优点,因而近年来在苔藓植物系统发育与进化研究中应用的越来越广泛。简要介绍了苔藓植物形态分类学所面临的一些问题和分子系统学研究常用的DNA序列分析方法,并将近年来该方法在苔藓植物分子系统学研究中的应用做了概述。     

鸟类的起源与恐龙

关于鸟类起源的争论,持续了一百多年之久,由于可依赖的论据没有突破性的进展,90年代初稍微平静了下来。然而石破天惊,近几年中国北方,尤其辽西地区相继发现了中国鸟、华夏鸟和朝阳鸟等大批早白垩世鸟类化石,特别是自1994年以来在朝阳北票地区晚侏罗世义县组底部发现了以孔子鸟为代表的原始鸟类群,使刚刚平静下来的鸟类起源争论烽火再起,而且有愈演愈烈     

揭秘辽西热河生物群中的古鸟类

“天空不留下鸟的痕迹,但我已经飞过”——这是泰戈尔诗集中的名句.当你仰望苍穹的时候,是否也会对着那片蔚蓝冥思苦想?亿万年前的空中,有哪些鸟儿曾振翅高飞?它们长什么模样?以什么为食?本文将带领大家走近辽西热河生物群,解读古鸟类化石这本无字史书. 在现生脊椎动物中,鸟类是仅次于鱼类的第二大类群,约有10000多种,广泛分布于世界各地.鸟类大多身披色彩斑斓的羽毛,拥有悦耳的叫声,并且善于飞行,因此深受人们的喜爱. 罕见的辽西热河古鸟化石 目前已知最原始的鸟是始祖鸟,发现于德国索伦霍芬地区上侏罗统地层中(距今约1.5亿年).从化石来看,始祖鸟同时具有鸟类和爬行动物的骨骼特征,因此被视为支持达尔文生物演化论的重要依据之一.这一观点得到普遍接受,同时也引发了关于鸟类起源与演化的激烈讨论.     

Evidence that Hensen's node is a site of retinoic acid synthesis.

Hensen's node of amniotes, like the Spemann organizer of amphibians, can induce a second body axis when grafted into a host embryo. The avian node, as well as several midline structures originating from it (notochord, floor plate), can also induce digit pattern duplications when grafted into the chick wing bud. We report here that the equivalent of Hensen's node from mouse is an effective inducer of digits in the chick wing bud. Tissues anterior and posterior to the node also evoke pattern duplications, but with a significantly lower efficiency. The finding that the murine node operates in an avian wing bud suggests that the same inducing agent(s) function in both primary and secondary embryonic fields and have been conserved during vertebrate evolution. Digit pattern duplications are also evoked by local administration of all-trans-retinoic acid. This similarity raises the possibility that Hensen's node is a source of retinoic acid. The mouse node is capable of synthesizing retinoic acid from its biosynthetic precursor all-trans-retinol at a substantially higher rate than either anterior or posterior tissues.     

鸟类分子生物学研究相关的Internet资源与常用软件

通过对互联网上的鸟类分子生物学资源进行数据挖掘、统计与分析,结果显示,当前鸟类的分子生物学研究资源已经相当丰富,尤其是在家鸡的全基因组测序之后,鸟类的分子生物学研究数据迅速上升,这一趋势仍将愈演愈烈.文中罗列了目前常用的互联网鸟类资源,以及相关软件的应用情况,对鸟类的基因组数据及基因组计划情况进行介绍与总结,相关信息通过表格形式详细列出.     

Clusters of iron-rich cells in the upper beak of pigeons are macrophages not magnetosensitive neurons

Understanding the molecular and cellular mechanisms that mediate magnetosensation in vertebrates is a formidable scientific problem. One hypothesis is that magnetic information is transduced into neuronal impulses by using a magnetite-based magnetoreceptor. Previous studies claim to have identified a magnetic sense system in the pigeon, common to avian species, which consists of magnetite-containing trigeminal afferents located at six specific loci in the rostral subepidermis of the beak. These studies have been widely accepted in the field and heavily relied upon by both behavioural biologists and physicists. Here we show that clusters of iron-rich cells in the rostro-medial upper beak of the pigeon Columbia livia are macrophages, not magnetosensitive neurons. Our systematic characterization of the pigeon upper beak identified iron-rich cells in the stratum laxum of the subepidermis, the basal region of the respiratory epithelium and the apex of feather follicles. Using a three-dimensional blueprint of the pigeon beak created by magnetic resonance imaging and computed tomography, we mapped the location of iron-rich cells, revealing unexpected variation in their distribution and number--an observation that is inconsistent with a role in magnetic sensation. Ultrastructure analysis of these cells, which are not unique to the beak, showed that their subcellular architecture includes ferritin-like granules, siderosomes, haemosiderin and filopodia, characteristics of iron-rich macrophages. Our conclusion that these cells are macrophages and not magnetosensitive neurons is supported by immunohistological studies showing co-localization with the antigen-presenting molecule major histocompatibility complex class II. Our work necessitates a renewed search for the true magnetite-dependent magnetoreceptor in birds.     

Avian sarcoma virus Y73 genome sequence and structural similarity of its transforming gene product to that of Rous sarcoma virus

From the complete nucleotide sequence of the genome of the avian sarcoma virus Y73, we have predicted amino acid sequence of p90 gag-yes, the product of the transforming gene. Contrary to previous evidence from molecular hybridization studies p90 gag-yes was found to have much homology with the transforming gene product p60 src of Rous sarcoma virus, suggesting that the cellular counterparts of the two (c-yes and c-src) originated from a common prototype sequence.     

Definitive fossil evidence for the extant avian radiation in the Cretaceous

Long-standing controversy surrounds the question of whether living bird lineages emerged after non-avian dinosaur extinction at the Cretaceous/Tertiary (K/T) boundary or whether these lineages coexisted with other dinosaurs and passed through this mass extinction event. Inferences from biogeography and molecular sequence data (but see ref. 10) project major avian lineages deep into the Cretaceous period, implying their 'mass survival' at the K/T boundary. By contrast, it has been argued that the fossil record refutes this hypothesis, placing a 'big bang' of avian radiation only after the end of the Cretaceous. However, other fossil data--fragmentary bones referred to extant bird lineages--have been considered inconclusive. These data have never been subjected to phylogenetic analysis. Here we identify a rare, partial skeleton from the Maastrichtian of Antarctica as the first Cretaceous fossil definitively placed within the extant bird radiation. Several phylogenetic analyses supported by independent histological data indicate that a new species, Vegavis iaai, is a part of Anseriformes (waterfowl) and is most closely related to Anatidae, which includes true ducks. A minimum of five divergences within Aves before the K/T boundary are inferred from the placement of Vegavis; at least duck, chicken and ratite bird relatives were coextant with non-avian dinosaurs.     

Molecular virology: was the 1918 flu avian in origin?

Taubenberger et al. claim that the 1918 influenza virus was derived from an avian source and adapted to humans shortly before the pandemic. However, we do not believe that this conclusion, which has been widely disseminated in the popular press and in scientific journals, is supported by their phylogenetic evidence.     

禽鹦鹉热衣原体实验室诊断技术的研究进展

摘要: 鹦鹉热衣原体是一种重要的人兽共患病病原,由于临床上缺少准确、快速、敏感的诊断方法和诊断试剂盒,严 重影响了该病原的确诊。因此,它对家禽、高危人群造成的危害易被忽视。本文就近年来对禽鹦鹉热衣原体实验 室诊断技术的研究进展作一综述,包括病原的抗原诊断、抗体诊断和分子诊断技术,为禽鹦鹉热衣原体的确诊和流 行病学调查提供技术支持。     

受分子寿命影响的中继最大可达传输速率

基于扩散的分子通信以分子作为信息载体进行信息的传输,分子在信道中做布朗运动,遵循菲克扩散定律.随着扩散距离的增加,分子浓度急速衰减,造成信道可达传输速率非常低,因此,可以采用中继传输来提高传输性能.鉴于扩散分子通信中继可达传输速率是业界研究的热点与难点,采用配体-受体结合机制,考虑分子寿命及分子到达概率等因素的影响,研究了基于扩散的分子通信中继信道对分子传输可达速率的影响,也探索了基于分子寿命的中继节点位置对中继可达传输速率的影响.仿真结果显示,随着分子寿命的增加,分子在信道中存在的时间增加,使得信道最大传输速率增大.同时,随着分子寿命的增加,中继节点需要靠向接收端,才能使信道最大传输速率达到最大.     

禽流感及其对经济社会影响的研究综述

综述了近年来国内外关于禽流感的发生与传播、社会经济影响及其风险评估方法研究进展.从野鸟、家鸭、水稻种植及交通贸易等角度归纳总结了各因素与禽流感发生及传播的关系,分析总结了禽流感发生造成的社会经济影响,探讨了基于这些影响下的风险评估方法.对已有研究,在研究方法、研究对象和研究范围等方面探讨了存在的问题及不足,展望了今后禽流感及其对经济社会影响的研究重点.