跳虫系统进化的研究进展

跳虫是弹尾纲（Collembola）的俗称,在所有六足动物中化石年代最早,因此跳虫是六足动物起源及进化研究中非常重要的类群。跳虫的起源、分类地位和系统关系等问题,对于阐明六足动物甚至节肢动物各大类群的系统关系非常关键,日益成为相关学者关注和争论的焦点。本文就跳虫形态学和分子系统学方面的研究工作进行了综述。     

低等六足动物系统学研究进展

低等六足动物包括原尾纲、弹尾纲和双尾纲三个类群,是探讨六足动物起源和进化问题的关键类群,近十年来成为节肢动物系统进化研究中的焦点之一。低等六足动物的系统发育地位以及它们之间的关系一直是备受争论的问题。通过介绍三类低等六足动物最新的分类系统,从经典分类学和系统发育两个方面对低等六足动物近十年来的研究进展进行了综述。迄今,对于三类低等六足动物都建立了比较完备的分类体系,原尾纲划分为3目10科,弹尾纲划分为4目30科,双尾纲划分为2亚目3总科10科。系统发育研究中,大多数的系统发育分析结果不支持传统的缺尾类假说,缺尾纲应摒弃不用。分子数据分析的结果普遍支持原尾纲与双尾纲近缘,但仍需要进一步探讨。线粒体基因组、比较胚胎学和比较精子学的研究结果表明,原尾纲可能经历了长期的趋异进化历史。最近的比较精子学研究支持了双尾纲的单系性。总之,三类低等六足动物系统学研究均取得了长足的发展,但仍然存在诸如研究人员匮乏和研究水平不均衡等问题。系统发育研究中,分子系统学研究成为关注的焦点,而基于核基因和线粒体基因的数据分别建立的系统发育假说存在分歧,亟需开发更优的数据分析方法。此外,需加强低等六足动物比较形态学、比较胚胎学、发育生物学等方面的研究,以便将来进行全证据的系统发育研究。     

有关节肢动物分类的几个问题

本文简要讨论了近年来有关节肢动物特别是昆虫高级分类研究中争论较大的几个关键问题,包括节肢动物的分类基础、“单肢亚门Ｕｎｉｒａｍｉａ”的单系性、六足总纲的单系性及昆虫纲（狭义）Ｉｎｓｅｃｔａ ｓ．ｓｔｒ．的范围等,以期引起我国动物学者的注意与重视。     

中国少足动物分类及其分布

我国对少足动物的研究起步较晚,直到近10年才渐有起色。目前,国际上对少足动物的研究仍集中于形态分类学,不过,随着物种描述和系统分类研究成果的积累,也陆续有区域性少足动物区系和分布的报道。本实验室自2006年起开展少足动物形态分类学研究,已报道少足动物1新属、19个新种和16个中国新纪录种。迄今,已记录和描述分布于我国的少足动物共计36种(包括3个未定名种),隶属于1目4科11属,即四少足目(Tetramerocerata),少足科(Pauropodidae)、广少足科(Eurypauropodidae)、短少足科(Brachypauropodidae)和球少足科(Sphaeropauropodidae),少足属(Pauropus)、别少足属(Allopauropus)、十别少足属(Decapauropus)、东泽络少足属(Donzelotauropus)、针少足属(Stylopauropus)、宋氏少足属(Songius)、广少足属(Eurypauropus)、三宝垄少足属(Samarangopus)、婆罗洲少足属(Borneopauropus)、短少足属(Brachypauropus)以及球少足属(Sphaeropauropus)。本文对我国现有少足动物的形态特征、分类和分布进行了综述,以期促进我国少足动物新种和新类群的发现,普及我国少足纲的系统分类学知识。     

昆明地区下寒武统沧浪铺组古虫动物新发现

文中详细描述昆明地区下寒武统沧浪铺组乌龙箐段古虫动物新种Vetulicola longbaoshanensis sp.nov.,并与相关属种作比较和讨论。古虫动物主要产于下寒武统筇竹寺组玉案山段的澄江动物群中,沧浪铺组乌龙箐段的地质年代较澄江动物群晚,该发现对研究古虫动物的演化具有重要意义。古虫动物的分类位置至今难以确定,争论的焦点多集中在古虫动物前体鳃囊的构造解释上。新材料鳃囊保存得完整清晰,为研究古虫动物的分类位置提供了新证据。     

六足动物分子系统学研究进展

对近期国内外六足总纲动物的原尾纲、弹尾纲、双尾纲和昆虫纲在种群遗传变异及进化、种及种下阶元的分类鉴定、种上阶元的系统发育分析等分子系统学方面的研究进展进行了综述。多基因的联合分子数据研究日益增加。随着分子技术的日益推广,不同类型的基因序列甚至全基因组的联合使用将引导分子系统学走向辉煌的未来。     

关于节肢动物系统分类与进化的分子佐证

从分子系统学方面就了肢动物系统进化及高级阶元分类研究中争论的关键问题进行比较分析。综述了该领域所取得的新进展,着重从分子水平来探讨节肢动物的起源与进化。     

国家自然科学基金委员会生命科学部2001年度资助重点科学基金项目一览表(26项)

项 目 名 称 申请者姓名 单 位 名 称野油菜黄单胞菌致病性的功能基因组学 唐纪良 广西大学低毒病毒的宿主因子基因和靶基因的克隆及其功能研究 陈保善 广西大学被子植物基部类群的结构、分化和系统学关系 路安民 中国科学院植物研究所现生六足动物高级阶元系统演化与分类地位的研究 尹文英 中国科学院上海昆虫研究所转“全鱼”生长激素基因鲤鱼的生态安全研究 汪亚平 中国科学院水生生物研究所受损常绿阔叶林生态系统退化机制的研究 宋永昌 华东师范大学朊蛋白（ＰｒＰ）糖基化和糖脂化修饰及其生物学功能的研究 董小平 中国预防医学科学院…     

六足总纲系统发育研究进展与新分类系统

简要综述了昆虫分纲、分目的历史变化,包括昆虫分目多少的变化,昆虫是纲级还是总纲级阶元的变化,昆虫各目分类地位系统排列的变化以及六足总纲系统发育研究进展。根据近10年来形态特征与分子测序数据相结合的系统发育研究,整理出六足总纲与系统发育支序分析相一致的分类系统,对昆虫35目的分类运用了10个分类阶元。在此基础上,删减次要分类阶元,提出简明分类系统,既反映每个高级分类单元的单系性,明晰各目的共祖近度,又减少了分类阶元层次,方便各分类单元的识别与鉴定。六足总纲Hexapoda分为4纲:原尾纲Protura(包括蚖目Acerentomata、华蚖目Sinentomata、古蚖目Eosentomata),弹尾纲Collembola(包括弹尾目Collembola),双尾纲Diplura(包括双尾目Diplura),昆虫纲Insecta。昆虫纲分为单髁亚纲SubclassMonocondylia(包括石蛃目Archaeognatha)与双髁亚纲SubclassDicondylia。双髁亚纲分为衣鱼部DivisionZygentoma(包括衣鱼目Zygentoma)与有翅部DivisionPterygota。有翅部分为10个总目、27目。     

双尾虫系统进化的初步探讨

双尾虫系统发生问题目前血受学者的关注。作为六足总纲中内,外颚亚纲的过渡类群,双尾虫是否单系性及其系统地位的确定是争论的焦点,也是解决六足总纲高级阶元系统关系的一个关键。文中综述了多年来双尾虫形态学和解剖学方面研究所引发的争议和达成的共识,并对近几年该方面分子系统学的工作进行了总结和初步探讨。     

Impact of the invasive shrub Amur honeysuckle (Lonicera maackii) on shrub-layer insects in a deciduous forest in the eastern United States

Invasive Amur honeysuckle (Lonicera maackii) creates a dense shrub layer in deciduous forests in eastern North America that negatively impacts native herbs and tree seedlings. We predicted that higher vegetative cover caused by this shrub would increase abundance and diversity of insects and alter composition of insect assemblages. We used paired plots, one with and one without honeysuckle, in ten forest locations in southwestern Ohio, USA, to sample insects and measure diversity and vertical cover of vegetation in the shrub layer. Vertical cover of this vegetation was higher on honeysuckle-present plots, but diversity of shrub-layer vegetation did not differ between honeysuckle-present and honeysuckle-absent plots. Species diversity of Hexapoda, Coleoptera, and Psocoptera, richness of Hexapoda, Coleoptera, Diptera, Hymenoptera, and Psocoptera, and abundance of Hexapoda, Diptera, Hymenoptera, and Psocoptera were higher on honeysuckle-present than on honeysuckle-absent plots. Evenness did not differ between honeysuckle treatments. Nonmetric multidimensional scaling distinguished taxonomic composition in honeysuckle-present plots from that in honeysuckle-absent plots. Presence of vertical cover explained higher richness of Hexapoda and Coleoptera, and higher abundance of Hexapoda, Diptera, Hymenoptera, and Psocoptera. Attributes of honeysuckle, independent of its contribution to vertical cover, explained increases in richness of Hexapoda, Coleoptera, and Hymenoptera and abundance of Hexapoda, Hymenopera, and Psocoptera. These attributes of honeysuckle could include a more complex vegetative structure, a greater availability of resources such as food, detritus, or shelter, and/or a more favorable cooler and moister microenvironment. To more fully understand the mechanisms causing increased richness and abundance of insects in honeysuckle-present areas, detailed studies on these attributes of honeysuckle would be necessary.     

A new view of insect-crustacean relationships II. Inferences from expressed sequence tags and comparisons with neural cladistics

The enormous diversity of Arthropoda has complicated attempts by systematists to deduce the history of this group in terms of phylogenetic relationships and phenotypic change. Traditional hypotheses regarding the relationships of the major arthropod groups (Chelicerata, Myriapoda, Crustacea, and Hexapoda) focus on suites of morphological characters, whereas phylogenomics relies on large amounts of molecular sequence data to infer evolutionary relationships. The present discussion is based on expressed sequence tags (ESTs) that provide large numbers of short molecular sequences and so provide an abundant source of sequence data for phylogenetic inference. This study presents well-supported phylogenies of diverse arthropod and metazoan outgroup taxa obtained from publicly-available databases. An in-house bioinformatics pipeline has been used to compile and align conserved orthologs from each taxon for maximum likelihood inferences. This approach resolves many currently accepted hypotheses regarding internal relationships between the major groups of Arthropoda, including monophyletic Hexapoda, Tetraconata (Crustacea + Hexapoda), Myriapoda, and Chelicerata sensu lato (Pycnogonida + Euchelicerata). "Crustacea" is a paraphyletic group with some taxa more closely related to the monophyletic Hexapoda. These results support studies that have utilized more restricted EST data for phylogenetic inference, yet they differ in important regards from recently published phylogenies employing nuclear protein-coding sequences. The present results do not, however, depart from other phylogenies that resolve Branchiopoda as the crustacean sister group of Hexapoda. Like other molecular phylogenies, EST-derived phylogenies alone are unable to resolve morphological convergences or evolved reversals and thus omit what may be crucial events in the history of life. For example, molecular data are unable to resolve whether a Hexapod-Branchiopod sister relationship infers a branchiopod-like ancestry of the Hexapoda, or whether this assemblage originates from a malacostracan-like ancestor, with the morphologically simpler Branchiopoda being highly derived. Whereas this study supports many internal arthropod relationships obtained by other sources of molecular data, other approaches are required to resolve such evolutionary scenarios. The approach presented here turns out to be essential: integrating results of molecular phylogenetics and neural cladistics to infer that Branchiopoda evolved simplification from a more elaborate ancestor. Whereas the phenomenon of evolved simplification may be widespread, it is largely invisible to molecular techniques unless these are performed in conjunction with morphology-based strategies.     

Molecular phylogeny of the major arthropod groups indicates polyphyly of crustaceans and a new hypothesis for the origin of hexapods

A phylogeny of the arthropods was inferred from analyses of amino acid sequences derived from the nuclear genes encoding elongation factor-1 alpha and the largest subunit of RNA polymerase II using maximum- parsimony, neighbor-joining, and maximum-likelihood methods. Analyses of elongation factor-1 alpha from 17 arthropods and 4 outgroup taxa recovered many arthropod clades supported by previous morphological studies, including Diplopoda, Myriapoda, Insecta, Hexapoda, Branchiopoda (Crustacea), Araneae, Tetrapulmonata, Arachnida, Chelicerata, and Malacostraca (Crustacea). However, counter to previous studies, elongation factor-1 alpha placed Malacostraca as sister group to the other arthropods. Branchiopod crustaceans were found to be more closely related to hexapods and myriapods than to malacostracan crustaceans. Sequences for RNA polymerase II were obtained from 11 arthropod taxa and were analyzed separately and in combination with elongation factor-1 alpha. Results from these analyses were concordant with those derived from elongation factor-1 alpha alone and provided support for a Hexapoda/Branchiopoda clade, thus arguing against the monophyly of the traditionally defined Atelocerata (Hexapoda + Myriapoda).      

Brain organization in Collembola (springtails)

Arthropoda is comprised of four major taxa: Hexapoda, Crustacea, Myriapoda and Chelicerata. Although this classification is widely accepted, there is still some debate about the internal relationships of these groups. In particular, the phylogenetic position of Collembola remains enigmatic. Some molecular studies place Collembola into a close relationship to Protura and Diplura within the monophyletic Hexapoda, but this placement is not universally accepted, as Collembola is also regarded as either the sister group to Branchiopoda (a crustacean taxon) or to Pancrustacea (crustaceans + hexapods). To contribute to the current debate on the phylogenetic position of Collembola, we examined the brains in three collembolan species: Folsomia candida, Protaphorura armata and Tetrodontophora bielanensis, using antennal backfills, series of semi-thin sections, and immunostaining technique with several antisera, in conjunction with confocal laser scanning microscopy and three-dimensional reconstructions. We identified several neuroanatomical structures in the collembolan brain, including a fan-shaped central body showing a columnar organization, a protocerebral bridge, one pair of antennal lobes with 20-30 spheroidal glomeruli each, and a structure, which we interpret as a simply organized mushroom body. The results of our neuroanatomical study are consistent with the phylogenetic position of Collembola within the Hexapoda and do not contradict the hypothesis of a close relationship of Collembola, Protura and Diplura.     

A new view of insect-crustacean relationships I. Inferences from neural cladistics and comparative neuroanatomy

Traditional hypotheses regarding the relationships of the major arthropod lineages focus on suites of comparable characters, often those that address features of the exoskeleton. However, because of the enormous morphological variety among arthropods, external characters may lead to ambiguities of interpretation and definition, particularly when species have undergone evolutionary simplification and reversal. Here we present the results of a cladistic analysis using morphological characters associated with brains and central nervous systems, based on the evidence that cerebral organization is generally robust over geological time. Well-resolved, strongly supported phylogenies were obtained from a neuromorphological character set representing a variety of discrete neuroanatomical traits. Phylogenetic hypotheses from this analysis support many accepted relationships, including monophyletic Chelicerata, Myriapoda, and Hexapoda, paraphyletic Crustacea and the union of Hexapoda and Crustacea (Tetraconata). They also support Mandibulata (Myriapoda + Tetraconata). One problematic result, which can be explained by symplesiomorphies that are likely to have evolved in deep time, is the inability to resolve Onychophora as a taxon distinct from Arthropoda. Crucially, neuronal cladistics supports the heterodox conclusion that both Hexapoda and Malacostraca are derived from a common ancestor that possessed a suite of discrete neural centers comprising an elaborate brain. Remipedes and copepods, both resolved as basal to Branchiopoda share a neural ground pattern with Malacostraca. These findings distinguish Hexapoda (Insecta) from Branchiopoda, which is the sister group of the clade Malacostraca + Hexapoda. The present study resolves branchiopod crustaceans as descendents of an ancestor with a complex brain, which means that they have evolved secondary simplification and the loss or reduction of numerous neural systems.     

A general theory of genital homologies for the Hexapoda (Pancrustacea) derived from skeletomuscular correspondences,with emphasis on the Endopterygota

No consensus exists for the homology and terminology of the male genitalia of the Hexapoda despite over a century of debate. Based on dissections and the literature, genital skeletomusculature was compared across the Hexapoda and contrasted with the Remipedia, the closest pancrustacean outgroup. The pattern of origin and insertion for extrinsic and intrinsic genitalic musculature was found to be consistent among the Ectognatha, Protura, and the Remipedia, allowing for the inference of homologies given recent phylogenomic studies. The penis of the Hexapoda is inferred to be derived from medially-fused primary gonopods (gonopore-bearing limbs), while the genitalia of the Ectognatha are inferred to include both the tenth-segmental penis and the ninth-segmental secondary gonopods, similar to the genitalia of female insects which comprise gonopods of the eighth and ninth segments. A new nomenclatural system for hexapodan genitalic musculature is presented and applied, and a general list of anatomical concepts is provided. Novel and refined homologies are proposed for all hexapodan orders, and a series of groundplans are postulated. Emphasis is placed on the Endopterygota, for which fine-grained transition series are hypothesized given observed skeletomuscular correspondences.     

The Tetraconata concept: hexapod-crustacean relationships and the phylogeny of Crustacea

A growing body of evidence indicates that Crustacea and Hexapoda are sister groups, rather than Hexapoda and Myriapoda. Some recent molecular data even suggest that Mandibulata is not monophyletic, with Myriapoda and Chelicerata instead being sister groups. Here, arguments for homology of the mandible throughout mandibulate arthropods and for a monophyletic Mandibulata will be presented, as well as arguments supporting the taxon Tetraconata (i.e. Crustacea + Hexapoda). The latter include molecular data (nuclear and mitochondrial ribosomal RNAs and protein coding genes), and morphological characters such as ommatidial structure, the presence of neuroblasts and a very similar axonogenesis of pioneer neurons. However, crustaceans are insufficiently sampled for the molecular data, and studies of neurogenesis are lacking for many crustacean taxa. Remipedia, Cephalocarida and Maxillopoda are particularly problematic. This is important for the entire problem, because monophyly of the Crustacea has not yet been proven beyond doubt and several molecular analyses suggest a paraphyletic Crustacea. Here, arguments for the monophyly of the Crustacea are reviewed and two alternatives for the relationships between the five higher taxa Remipedia, Cephalocarida, Maxillopoda, Branchiopoda and Malacostraca are discussed: the Entomostraca concept sensu Walossek with Malacostraca as sister group to Cephalocarida, Maxillopoda and Branchiopoda, and the Thoracopoda concept sensu Hessler with Cephalocarida, Branchiopoda and Malacostraca forming a monophylum.     

MicroRNA evolution provides new evidence for a close relationship of Diplura to Insecta

The phylogenetic interrelationships among four hexapod lineages (Protura, Collembola, Diplura and Insecta) are pivotal to understanding the origin of insects and the early diversification of Hexapoda, but they have been difficult to clarify based on the available data. In this study, we identified 91 conserved microRNA (miRNA) families from 36 panarthropod taxa, including seven newly sequenced non-insect hexapods. We found major clade differentiation accompanied by the origin of novel miRNA families, and most miRNA clusters are conserved with a high degree of microsynteny. Importantly, we were able to identify two miRNA families unique to Hexapoda, and four miRNA families and a miRNA cluster that exist exclusively in Diplura and Insecta, suggesting a close relationship between Diplura and Insecta as well as the monophyly of Hexapoda. Combined with a phylogenetic analysis based on the presence/absence matrix of miRNA families, our study demonstrates the effectiveness of miRNA in resolving deep phylogenetic problems.     

From variable to constant cell numbers: cellular characteristics of the arthropod nervous system argue against a sister-group relationship of Chelicerata and “Myriapoda” but favour the Mandibulata concept

In the new debate on arthropod phylogeny, structure and development of the nervous system provide important arguments. The architecture of the brain of Hexapoda, Crustacea and Chelicerata in recent years has been thoroughly compared against an evolutionary background. However, comparative aspects of the nervous systems in these taxa at the cellular level have been examined in only a few studies. This review sets out to summarize these aspects and to analyse the existing data with respect to the concept of individually identifiable neurons. In particular, mechanisms of neurogenesis, the morphology of serotonergic interneurons, the number of motoneurons, and cellular features and development of the lateral eyes are discussed. We conclude that in comparison to the Mandibulata, in Chelicerata the numbers of neurons in the different classes examined are much higher and in many cases are not fixed but variable. The cell numbers in Mandibulata are lower and the majority of neurons are individually identifiable. The characters explored in this review are mapped onto an existing phylogram, as derived from brain architecture in which the Hexapoda are an in-group of the Crustacea, and there is not any conflict of the current data with such a phylogenetic position of the Hexapoda. Nevertheless, these characters argue against a sister-group relationship of Myriapoda and Chelicerata as has been recently suggested in several molecular studies, but instead provide strong evidence in favour of the Mandibulata concept.Edited by D. Tautz     

Mitochondrial genomes suggest that hexapods and crustaceans are mutually paraphyletic

For over a century the relationships between the four major groups of the phylum Arthropoda (Chelicerata, Crustacea, Hexapoda and Myriapoda) have been debated. Recent molecular evidence has confirmed a close relationship between the Crustacea and the Hexapoda, and has included the suggestion of a paraphyletic Hexapoda. To test this hypothesis we have sequenced the complete or near-complete mitochondrial genomes of three crustaceans (Parhyale hawaiensis, Squilla mantis and Triops longicaudatus), two collembolans (Onychiurus orientalis and Podura aquatica) and the insect Thermobia domestica. We observed rearrangement of transfer RNA genes only in O. orientalis, P. aquatica and P. hawaiensis. Of these, only the rearrangement in O. orientalis, an apparent autapomorphy for the collembolan family Onychiuridae, was phylogenetically informative.We aligned the nuclear and amino acid sequences from the mitochondrial protein-encoding genes of these taxa with their homologues from other arthropod taxa for phylogenetic analysis. Our dataset contains many more Crustacea than previous molecular phylogenetic analyses of the arthropods. Neighbour-joining, maximum-likelihood and Bayesian posterior probabilities all suggest that crustaceans and hexapods are mutually paraphyletic. A crustacean clade of Malacostraca and Branchiopoda emerges as sister to the Insecta sensu stricto and the Collembola group with the maxillopod crustaceans. Some, but not all, analyses strongly support this mutual paraphyly but statistical tests do not reject the null hypotheses of a monophyletic Hexapoda or a monophyletic Crustacea. The dual monophyly of the Hexapoda and Crustacea has rarely been questioned in recent years but the idea of both groups' paraphyly dates back to the nineteenth century. We suggest that the mutual paraphyly of both groups should seriously be considered.