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。     

从核糖体RNA基因序列探讨双尾虫的系统进化

双尾虫是否单系, 以及双尾虫与其他六足动物系统关系是多年来动物分类学家争议的一个关键问题. 测定了双尾虫的两大类群: 康虫八类和铗虫八类, 以及原尾虫、跳虫和蝗虫等核糖体RNA基因18SrDNA全序列和28SrDNA部分序列(D3~D5区), 并选用甲壳动物卤虫为外群, 采用最大简约(MP)法构建分子系统树. 结果表明: (ⅰ) 18SrDNA和28SrDNA数据整合分析含有较强的系统发育信息, 支持双尾虫单系性观点; (ⅱ) 双尾虫与原尾虫在系统树中构成姊妹群, 且支持率很高.     

不同垦复方式油茶林土壤节肢动物多样性特征

【目的】油茶新造林特别是纯林不断骤增导致油茶林害虫发生日趋严重,食用茶油安全倍受威胁。为探索有效控制油茶林害虫发生的途径,保护分解者跳虫等土壤节肢动物多样性。【方法】基于Tullgren干漏斗法和巴氏罐法,对半垦复油茶幼林、全垦复油茶幼林、全垦复油茶成林和未垦复油茶成林4种不同油茶林的20个土样和15个凋落物样中的土壤跳虫和土壤其他节肢动物多样性特征进行了研究。【结果】共分离出跳虫315头,隶属6科8属;其他土壤节肢动物11科17种295头。多样性分析结果表明,油茶成林地比幼林地土壤动物的多样性指数高,多样化的地被物有利于提高土壤动物的多样性,垦复和施肥等人为干扰显著地降低土壤跳虫的多样性,却有利于增加罐诱土壤动物的多样性,水源是土壤动物生存的关键因子,对林地跳虫和罐诱动物的多样性提高有显著促进作用。【结论】探明了不同垦复类型油茶林土壤跳虫和土壤其他罐诱节肢动物多样性特征,对合理开展油茶林垦复,发挥油茶林土壤跳虫和土壤节肢动物分解功能提供了科学依据。     

长春净月潭不同林型土壤跳虫组成的研究

<正> 跳虫是土壤动物主要类群之一,与螨类一起约占土壤动物的80％,在1m~2土壤内跳虫多达上百万。跳虫具有分解生物残体,促进土壤形成,传播细菌的作用。在卫生昆虫上占有一     

有关六足动物（昆虫）系统分类中的争论热点

六足动物即昆虫的泛称，自寒武纪以来就是地球上物种最多的一个类型，近来分类学家们，从形态分类研究和分子分类研究两方面，对六足动物的系统渊源展开了热烈的争论，本文仅简单介绍其中几个争论要点。     

长春净月潭地区土壤跳虫的生态分布

土壤动物直接参与土壤形成,它与土壤微生物的相互配合,对植物凋落物的分解起着十分重要的作用。土壤跳虫是土壤动物中最重要的类群之一。关于它的生态分布,目前国内报道不多。东北师范大学和日本九州大学合作,对长春净月潭地区的土壤跳虫进行了初步调查。     

松嫩草原区农牧林复合系统中小型土壤动物群落生态研究

通过野外选择样地,设置样方,调查了温带地区松嫩草原区农牧林复合系统中小型土壤动物群落的生态特征．结果表明,中小型土壤动物的优势类群是球角跳虫科(Hypogastruridae)、辐螨(Actinedida)、革螨(Gamasida)和甲螨(Oribatida),常见类群是节跳虫科(Isotomidae)和叶蝉科(Jassidae),从玉米田、草地和杨树林3个子系统的对比分析看,草地物种最丰富,多样性最高,生境条件最优越,中小型土壤动物的个体数和类群数随土层深度的增加而递减,表聚性明显;但3个子系统的垂直分布特征不完全相同,运用主成分分析方法,分析了主要土壤环境要素和气侯要素与中小型土壤节肢动物群落的相关关系,发现土壤环境要素是影响中小型土壤动物群落的主导因子。     

三江平原农田土壤跳虫多尺度空间自相关性

土壤动物多尺度空间自相关性特征是土壤动物空间异质性和空间共存格局研究的重要基础。以土壤跳虫为研究对象,以中国科学院三江平原沼泽湿地生态实验站为研究区,于2011年8月和10月,选取具30 a以上耕作历史的旱地为实验样地,以5 m为步长设置一个50 m×50 m的实验样地,采用地统计中的全局Moran's I指数和局部Moran's I指数相结合的方法,研究土壤跳虫多尺度空间自相关性特征。全局空间自相关结果表明,土壤跳虫群落总密度和多数跳虫种类存在显著的多尺度空间自相关特征,多数为显著的正的空间自相关性,形成明显的空间集群。局部空间自相关结果表明,土壤跳虫群落总密度和所有跳虫种类均存在显著的局部空间自相关性,在局部地区形成"高—高"和/或"低—低"的空间集群,并和"高—低"和/或"低—高"的空间孤立区相伴发生,即形成"斑块"和"孔隙"相间分布的水平镶嵌格局;这种镶嵌格局具一定的时间动态特征,从夏季到秋季斑块大小和空间分布范围略有变化。研究表明,土壤跳虫具有明显的多尺度空间自相关性;空间集群是土壤跳虫的常见空间分布格局,在样地内形成"斑块"和"孔隙"相间分布的水平镶嵌格局,这种格局具年内时间变异性。     

长白山苔原带土壤动物群落结构及多样性

长白山苔原生态系统对环境变化非常敏感,一旦破坏很难恢复。土壤动物是陆地生态系统的重要组成部分,联系着地上和地下生态系统。为探讨长白山苔原带土壤动物群落的组成、结构和多样性特征,于2009年5月、7月和9月对上部和下部苔原带土壤动物进行了研究。研究表明:长白山整个苔原带土壤动物优势类群为甲螨亚目、节跳虫科和球角跳虫科。下部苔原亚带土壤动物个体数和类群数多,群落结构较为复杂。土壤动物的个体数随生境和时间变化有很大波动,类群数变化则较小。在7月份个体数最少,而类群数随着时间的变化有减少的趋势。土壤动物的垂直分布随时间和生境的不同而异。上部苔原亚带9月的甲螨亚目(P﹤0.01)、革螨亚目(P﹤0.05)及下部苔原亚带5月的甲螨亚目、革螨亚目、辐螨亚目(P=0.03,P=0.011,P=0.027)0—5 cm土层显著高于凋落物层;下部苔原亚带5月的球角跳虫科(P=0.001)及各月的节跳虫科和山跳虫科在各层之间存在显著差异(P=0.001,P=0.036,P=0.005,P=0.001,P=0.04,P=0.009)。两个亚带土壤动物多样性随时间的变化都有递减的趋势。土壤动物的多样性指数、丰富度指数和均匀度指数均是下部苔原亚带高于上部苔原亚带,而优势度指数则相反。相似性指数表明两个亚带土壤动物群落组成上存在一定的差异,各类群的相对数量差异在9月最大。下部苔原亚带的生境条件较适宜土壤动物生存,生物多样性较高。     

苔藓动物的起源与系统发生研究进展—形态学和分子生物学的证据

苔藓动物是后生动物中的一个重要类群。然而,和其它主要后生动物类群相比,长期以来对它的系统学研究却相对滞后。其起源,系统发生地位以及与其它后生物门类之间、其内部各高级分类群间的谱系发生关系一直存在争议。一般认为它是介于原口动物和后口动物之间的过渡类群。但是,近年来的分子系统学研究已经证实了它的原口归属。古生物学资料表明,虽然苔藓动物的大多数类群在奥陶纪已经分化出来,但它在寒武纪却缺乏任何化石记录。另外,苔藓动物起源的时间和方式、其内部各类群间的系统发生关系特别是现生类群和化石类群之间的关系等诸多问题的解决,还有待于大量的形态学和不同的分子数据的进一步积累,并结合其地层分布等各种相关资料进行综合研究。     

Towards an 18S phylogeny of hexapods: accounting for group-specific character covariance in optimized mixed nucleotide/doublet models

The phylogenetic diversification of Hexapoda is still not fully understood. Morphological and molecular analyses have resulted in partly contradicting hypotheses. In molecular analyses, 18S sequences are the most frequently employed, but it appears that 18S sequences do not contain enough phylogenetic signals to resolve basal relationships of hexapod lineages. Until recently, character interdependence in these data has never been treated seriously, though possibly accounting for the occurrence of biased results. However, software packages are readily available which can incorporate information on character interdependence within a Bayesian approach. Accounting for character covariation derived from a hexapod consensus secondary structure model and applying mixed DNA/RNA substitution models, our Bayesian analysis of 321 hexapod sequences yielded a partly robust tree that depicts many hexapod relationships congruent with morphological considerations. It appears that the application of mixed DNA/RNA models removes many of the anomalies seen in previous studies. We focus on basal hexapod relationships for which unambiguous results are missing. In particular, the strong support for a “Chiastomyaria” clade (Ephemeroptera+Neoptera) obtained in Kjer's [2004. Aligned 18S and insect phylogeny. Syst. Biol. 53, 1–9] study of 18S sequences could not be confirmed by our analysis. The hexapod tree can be rooted with monophyletic Entognatha but not with a clade Ellipura (Collembola+Protura). Compared to previously published contributions, accounting for character interdependence in analyses of rRNA data presents an improvement of phylogenetic resolution. We suggest that an integration of explicit clade-specific rRNA structural refinements is not only possible but an important step in the optimization of substitution models dealing with rRNA data.     

New insight into the systematics of Tomoceridae (Hexapoda,Collembola) by integrating molecular and morphological evidence

Tomoceridae is common but among the most problematic groups of Collembola. Its position within Collembola and the relationships within the family remain obscure. This also extends to the generic division of the subfamily Tomocerinae that remains controversial. This study examines these issues by integrating both molecular and morphological evidence. Our molecular phylogeny based on rDNA sequences supports the monophyly of Tomoceridae and the sister relationship between Tomocerinae and Lepidophorellinae. Reconstructions and tree topology tests constraining monophyly did not resolve the relationships between Tomoceridae and other collembolan groups. We also examined the morphology of the first instar (primary) larvae, which has significant phylogenetic value among higher Collembola. Mapping primary chaetotaxy onto our molecular phylogeny provided further evidence for the unique position of Tomoceridae within Entomobryomorpha and Collembola. The monophyly and subfamilial classification within Tomoceridae were validated here, whereas its position among Collembola will need further studies in a broader consideration across the major collembolan orders. Within Tomocerinae, the monophyly of Pogonognathellus was demonstrated, but the status of Tomocerus and Tomocerina is still to be resolved.     

Testing for misleading effects in the phylogenetic reconstruction of ancient lineages of hexapods: influence of character dependence and character choice in analyses of 28S rRNA sequences

The present analyses employ the almost complete sequence of the 28S rRNA gene to investigate phylogenetic relationships among Pancrustacea, placing special emphasis on the position of basal hexapod lineages. This study utilizes a greater number of characters and taxa of Protura, Collembola and Diplura than previous analyses to focus on conflicts in the reconstruction of the early steps in hexapod evolution. Phylogenetic trees are mainly based on Bayesian approaches, but likewise include analyses with Maximum Likelihood and Maximum Parsimony. Different analyses, including the application of a mixed DNA/RNA substitution model, were performed to narrow possible misleading effects of non-stationarity of nucleotide frequencies, saturation and character independence down to a minimum. This is the first time that a mixed DNA/RNA model is applied to analyse 28S rRNA sequences of basal hexapods. All methods yielded strong support for the monophyly of Collembola, Diplura, Dicondylia and Insecta s.str. , as well as for a cluster composed of Diplura and Protura ('Nonoculata-hypothesis'). However, the last cluster may be an artifact caused by a shared GC bias of the 28S sequences between these orders, in combination with a long branch effect. The instability of the position of the 'Nonoculata' within Pancrustacea further bears out the misleading effect of non-stationarity of nucleotide frequencies. Protura and Diplura either form the sister-group to Collembola (Entognatha) or cluster with branchiopod crustaceans. Overall, the phylogenetic signal of the complete sequences of the 28S rRNA gene favours monophyly of Hexapoda over paraphyly. However, further corroboration from independent data is needed to rule out the competing hypothesis of mutually paraphyletic Crustacea and Hexapoda.     

The Phylogeny of the Extant Hexapod Orders

Morphological and molecular data are marshalled to address the question of hexapod ordinal relationships. The combination of 275 morphological variables, 1000 bases of the small subunit nuclear rDNA (18S), and 350 bases of the large subunit nuclear rDNA (28S) are subjected to a variety of analysis parameters (indel and transversion costs). Representatives of each hexapod order are included with most orders represented multiply. Those parameters that minimize character incongruence (ILD of Mickevich and Farris, 1981, Syst. Zool. 30, 351–370), among the morphological and molecular data sets are chosen to generate the best supported cladogram. A well-resolved and robust cladogram of ordinal relationships is produced with the topology (Crustacea ((Chilopoda Diplopoda) ((Collembola Protura) ((Japygina Campodeina) (Archaeognatha (Zygentoma (Ephemerida (Odonata ((((Mantodea Blattaria) Isoptera) Zoraptera) ((Plecoptera Embiidina) (((Orthoptera Phasmida) (Grylloblattaria Dermaptera)) ((((Psocoptera Phthiraptera) Thysanoptera) Hemiptera) ((Neuropteroidea Coleoptera) (((((Strepsiptera Diptera) Mecoptera) Siphonaptera) (Trichoptera Lepidoptera)) Hymenoptera)))))))))))))).     

Mitochondrial genome data alone are not enough to unambiguously resolve the relationships of Entognatha, Insecta and Crustacea sensu lato (Arthropoda)

An analysis of the relationships of the major arthropod groups was undertaken using mitochondrial genome data to examine the hypotheses that Hexapoda is polyphyletic and that Collembola is more closely related to branchiopod crustaceans than insects. We sought to examine the sensitivity of this relationship to outgroup choice, data treatment, gene choice and optimality criteria used in the phylogenetic analysis of mitochondrial genome data. Additionally we sequenced the mitochondrial genome of an archaeognathan, Nesomachilis australica, to improve taxon selection in the apterygote insects, a group poorly represented in previous mitochondrial phylogenies. The sister group of the Collembola was rarely resolved in our analyses with a significant level of support. The use of different outgroups (myriapods, nematodes, or annelids + mollusks) resulted in many different placements of Collembola. The way in which the dataset was coded for analysis (DNA, DNA with the exclusion of third codon position and as amino acids) also had marked affects on tree topology. We found that nodal support was spread evenly throughout the 13 mitochondrial genes and the exclusion of genes resulted in significantly less resolution in the inferred trees. Optimality criteria had a much lesser effect on topology than the preceding factors; parsimony and Bayesian trees for a given data set and treatment were quite similar. We therefore conclude that the relationships of the extant arthropod groups as inferred by mitochondrial genomes are highly vulnerable to outgroup choice, data treatment and gene choice, and no consistent alternative hypothesis of Collembola's relationships is supported. Pending the resolution of these identified problems with the application of mitogenomic data to basal arthropod relationships, it is difficult to justify the rejection of hexapod monophyly, which is well supported on morphological grounds. © The Willi Hennig Society 2004.     

Revealing pancrustacean relationships: Phylogenetic analysis of ribosomal protein genes places Collembola (springtails) in a monophyletic Hexapoda and reinforces the discrepancy between mitochondrial and nuclear DNA markers

Background  

In recent years, several new hypotheses on phylogenetic relations among arthropods have been proposed on the basis of DNA sequences. One of the challenged hypotheses is the monophyly of hexapods. This discussion originated from analyses based on mitochondrial DNA datasets that, due to an unusual positioning of Collembola, suggested that the hexapod body plan evolved at least twice. Here, we re-evaluate the position of Collembola using ribosomal protein gene sequences.     

Is Ellipura monophyletic? A combined analysis of basal hexapod relationships with emphasis on the origin of insects

Hexapoda includes 33 commonly recognized orders, most of them insects. Ongoing controversy concerns the grouping of Protura and Collembola as a taxon Ellipura, the monophyly of Diplura, a single or multiple origins of entognathy, and the monophyly or paraphyly of the silverfish (Lepidotrichidae and Zygentoma s.s.) with respect to other dicondylous insects. Here we analyze relationships among basal hexapod orders via a cladistic analysis of sequence data for five molecular markers and 189 morphological characters in a simultaneous analysis framework using myriapod and crustacean outgroups. Using a sensitivity analysis approach and testing for stability, the most congruent parameters resolve Tricholepidion as sister group to the remaining Dicondylia, whereas most suboptimal parameter sets group Tricholepidion with Zygentoma. Stable hypotheses include the monophyly of Diplura, and a sister group relationship between Diplura and Protura, contradicting the Ellipura hypothesis. Hexapod monophyly is contradicted by an alliance between Collembola, Crustacea and Ectognatha (i.e., exclusive of Diplura and Protura) in molecular and combined analyses.     

Phylogenetic Distribution of Extant Richness Suggests Metamorphosis Is a Key Innovation Driving Diversification in Insects

Insects and their six-legged relatives (Hexapoda) comprise more than half of all described species and dominate terrestrial and freshwater ecosystems. Understanding the macroevolutionary processes generating this richness requires a historical perspective, but the fossil record of hexapods is patchy and incomplete. Dated molecular phylogenies provide an alternative perspective on divergence times and have been combined with birth-death models to infer patterns of diversification across a range of taxonomic groups. Here we generate a dated phylogeny of hexapod families, based on previously published sequence data and literature derived constraints, in order to identify the broad pattern of macroevolutionary changes responsible for the composition of the extant hexapod fauna. The most prominent increase in diversification identified is associated with the origin of complete metamorphosis, confirming this as a key innovation in promoting insect diversity. Subsequent reductions are recovered for several groups previously identified as having a higher fossil diversity during the Mesozoic. In addition, a number of recently derived taxa are found to have radiated following the development of flowering plant (angiosperm) floras during the mid-Cretaceous. These results reveal that the composition of the modern hexapod fauna is a product of a key developmental innovation, combined with multiple and varied evolutionary responses to environmental changes from the mid Cretaceous floral transition onward.     

The phylogenetic interrelationships of the higher taxa of apterygote hexapods

The phylogeny of the basal hexapods, the so-called apterygote insects, was studied using parsimony analysis procedures. Most analyses took into account 47 characters mainly based on external morphology, and 19 taxa including 14 apterygote representatives, 3 pterygotes and also 2 distantly related myriapods were used as outgroups. The binary and multistate characters are discussed in detail and treated as unordered and equally weighted. Other analyses were performed using a second data set in which 28 characters, based on internal anatomy and already used in a previous work ( Bitsch & Bitsch 1998 ), were added to the first data set. This second matrix was restricted to 12 terminal taxa, the same as those of our previous work. The results of the different analyses are generally congruent. They strongly support the monophyly of several orders (Protura, Collembola, Archaeognatha) and of two groupings (Ectognatha, Dicondylia). Three other assemblages (Ellipura, Diplura, Entognatha) appear as parsimonious phylogenetic hypotheses, but they are never supported by the cladistical analyses and are based on a very small number of autapomorphies; so, the monophyly of each of them is not firmly established. Archaeognatha appears as the sister group of the Dicondylia. The three unresolved representatives of the Zygentoma are found as the sister group of the Pterygota. The results are discussed in the light of current concepts in hexapod phylogeny.