Trace fossils of Cambrian aglaspidid arthropods

A new trace fossil, Raaschichnus gundersoni , from the Upper Cambrian St. Lawrence Formation of Wisconsin, was produced by an aglaspidid arthropod. The rusophyciform trace, which occurs singly and in series, is distinctive in showing marks left by the tail-spine. Other trace fossils previously considered to have been made by aglaspidids were probably excavated by animals lacking a tail-spine and with appendage morphologies very different from the aglaspidids of Wisconsin.     

The cuticle of the aglaspidid arthropods, a red-herring in the early history of the vertebrates

The supposed early vertebrate Anatolepis has recently been reinterpreted by Peel (1979; Rapp. Gr∅nl. Geol. Unders. 91 ) as an arthropod, probably aglaspidid. The cuticle of Aglaspis shows a characteristic arthropodan structure, including laminations and ducts, but it is apparently composed of primary phosphate. Apart from composition, the skeletal histology of Anatolepis is totally different, and this, together with more general considerations, eliminates any possibility of arthropod affinity. Anatolepis remains the earliest known vertebrate. Aglaspididae, cuticle, ultrastructure, Vertebrata, Upper Cambrian.     

Hox genes and the phylogeny of the arthropods

The arthropods are the most speciose, and among the most morphologically diverse, of the animal phyla. Their evolution has been the subject of intense research for well over a century, yet the relationships among the four extant arthropod subphyla - chelicerates, crustaceans, hexapods, and myriapods - are still not fully resolved. Morphological taxonomies have often placed hexapods and myriapods together (the Atelocerata) [1, 2], but recent molecular studies have generally supported a hexapod/crustacean clade [2-9]. A cluster of regulatory genes, the Hox genes, control segment identity in arthropods, and comparisons of the sequences and functions of Hox genes can reveal evolutionary relationships [10]. We used Hox gene sequences from a range of arthropod taxa, including new data from a basal hexapod and a myriapod, to estimate a phylogeny of the arthropods. Our data support the hypothesis that insects and crustaceans form a single clade within the arthropods to the exclusion of myriapods. They also suggest that myriapods are more closely allied to the chelicerates than to this insect/crustacean clade.     

Patterns within patterns: abundance-size relationships within the Hemiptera of tropical rain forest or why phylogeny matters

Our data are for a large composite sample of bugs (Insecta Hemiptera and Homoptera) from a tropical rain forest area in Sulawesi, Indonesia, collected by various sampling techniques at several representative localities over one year. We demonstrate how an overall relationship between log abundance and log body length in a large sample, which at first sight might appear to be of the polygonal form identified by Blackburn and Gaston, can be broken down into a consistent series of stronger linear relationships based around the composition of taxonomic clades with differing gradients. Furthermore, we show that the number of species within superfamily/family clades is negatively related to the mean body size of the clade, suggesting that taxa with a small body size tend to be represented by more species, thus further distorting the form of any overall relationship. The significance of these findings is discussed in the context of the current debate about species abundance, species size and distribution area relationships.     

水螨群总科阶元系统发育的支序分析 (蜱螨亚纲：水螨群)

对水螨群9总科进行了系统发育分析,支序分析选用了23个形态学特征和3个生物学特征。据分析结果所揭示的9总科间的系统发育关系和姐妹群关系,将水螨群9总科划分为5类：拟水螨类,含冥绒螨总科;始水螨类,含溪螨总科;真水螨类,含古水螨类和新水螨类;古水螨类,含水螨总科、盾水螨总科和皱喙螨总科;新水螨类,含刺触螨总科、腺水螨总科、湿螨总科和雄尾螨总科。类间姐妹群关系为：拟水螨类与始水螨类+真水螨类为姐妹群,始水螨类与真水螨类(古水螨类+新水螨类)为姐妹群,古水螨类与新水螨类为姐妹群。该文还就所提出的水螨群5类9总科的阶元排列建议与已有的观点进行了比较。     

Phylogenetic relationships of the Wolbachia of nematodes and arthropods

Wolbachia are well known as bacterial symbionts of arthropods, where they are reproductive parasites, but have also been described from nematode hosts, where the symbiotic interaction has features of mutualism. The majority of arthropod Wolbachia belong to clades A and B, while nematode Wolbachia mostly belong to clades C and D, but these relationships have been based on analysis of a small number of genes. To investigate the evolution and relationships of Wolbachia symbionts we have sequenced over 70 kb of the genome of wOvo, a Wolbachia from the human-parasitic nematode Onchocerca volvulus, and compared the genes identified to orthologues in other sequenced Wolbachia genomes. In comparisons of conserved local synteny, we find that wBm, from the nematode Brugia malayi, and wMel, from Drosophila melanogaster, are more similar to each other than either is to wOvo. Phylogenetic analysis of the protein-coding and ribosomal RNA genes on the sequenced fragments supports reciprocal monophyly of nematode and arthropod Wolbachia. The nematode Wolbachia did not arise from within the A clade of arthropod Wolbachia, and the root of the Wolbachia clade lies between the nematode and arthropod symbionts. Using the wOvo sequence, we identified a lateral transfer event whereby segments of the Wolbachia genome were inserted into the Onchocerca nuclear genome. This event predated the separation of the human parasite O. volvulus from its cattle-parasitic sister species, O. ochengi. The long association between filarial nematodes and Wolbachia symbionts may permit more frequent genetic exchange between their genomes.     

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.     

The colonization of land by animals: molecular phylogeny and divergence times among arthropods

Background  

The earliest fossil evidence of terrestrial animal activity is from the Ordovician, ~450 million years ago (Ma). However, there are earlier animal fossils, and most molecular clocks suggest a deep origin of animal phyla in the Precambrian, leaving open the possibility that animals colonized land much earlier than the Ordovician. To further investigate the time of colonization of land by animals, we sequenced two nuclear genes, glyceraldehyde-3-phosphate dehydrogenase and enolase, in representative arthropods and conducted phylogenetic and molecular clock analyses of those and other available DNA and protein sequence data. To assess the robustness of animal molecular clocks, we estimated the deuterostome-arthropod divergence using the arthropod fossil record for calibration and tunicate instead of vertebrate sequences to represent Deuterostomia. Nine nuclear and 15 mitochondrial genes were used in phylogenetic analyses and 61 genes were used in molecular clock analyses.     

Squamate phylogeny and the relationships of snakes and mosasauroids

Cladistic analysis of extant and fossil squamates (95 characters, 26 taxa) finds the fossil squamate, Coniasaurus Owen, 1850, to be the sister-group of the Mosasauroidea (mosasaurs and aigialosaurs). This clade is supported in all 18 shortest cladograms (464 steps; CI 0.677; HI 0.772) by nine characters of the dermatocranium, maxilla, and mandible. A Strict Consensus Tree of the 18 shortest trees collapses to a basal polytomy for most major squamate clades including the clade (Coniasaurus, Mosasauroidea). A Majority Rule Consensus Tree shows that, in 12 of 18 shortest cladograms, the clade Coniasaurus- Mosasauroidea is the sister-group to snakes (Scolecophidia (Alethinophidia, Dinilysia); this entire clade, referred to as the Pythonomorpha ([[Scolecophidia [Alethinophidia, Dinilysia]], [Coniasaurus, Mosasauroidea]]) is the sister-group to all other scleroglossans. Pythonomorpha is supported in these 12 cladograms by nine characters related to the lower jaw and cranial kinesis. In 6 of 18 shortest cladograms, snakes are the sister-group to the clade (Amphisbaenia (Dibamidae (Gekkonoidea, Eublepharidae))). None of the cladograms support the hypothesis that coniasaurs and mosasauroids are derived varanoid anguimorphs. Two additional analyses were conducted: (1) manipulation and movement of problematic squamate clades while constraining ‘accepted’ relationships; (2) additional cladistic analyses beginning with extant taxa, and sequentially adding fossil taxa. From Test I, at 467 steps, Pythonomorpha can be the sister-group to the Anguimorpha, Scincomorpha, ‘scinco-gekkonomorpha’ [scincomorphs, gekkotans, and amphibaenids-dibamids]. At 471 steps Pythonomorpha can be placed within Varanoidea. Treating only mosasauroids and coniasaurs as a monophyletic group: 469 steps, mosasauroids and coniasaurs as sister-group to Anguimorpha; 479 steps, mosasauroids and coniasaurs nested within Varanoidea. Test II finds snakes to nest within Anguimorpha in a data set of only Mosasauroidea + Extant Squamates; the sistergroup to snakes + anugimorphs is (Amphisbaenia (Dibarnidae (Gekkonoidea, Eublepharidae))). No one particular taxon is identified as a keystone taxon in this analysis, though it appears truc that fossil taxa significantly alter the structure of squamate phylogenetic trees.     

The seasonality of arboreal arthropods foraging within an Australian rainforest tree

Abstract.

• 1 The seasonality of arboreal arthropods foraging within the crown of the canopy tree Argyrodendron actinophyllum. Edlin (Sterculiaceae) was studied in a subtropical rain forest near Brisbane, Australia, during 2 years with interception traps and restricted canopy fogging.
• 2 Minimal air temperatures explained most of the seasonal variance in arthropod‘density activity'. However, the host phenology was important for several phytophagous groups. Rainfall, relative humidity and lunar phase influenced arthropod activity slightly.
• 3 Seasonal ranges were significantly different among arboreal guilds and were related to food resource availability in time, associated with both the host and the rainforest environment. Seasonal peaks of herbivores were more marked than in tropical rain forests, but less sharp than in temperate woodlands.'
• 4 Quantitative changes in arthropod density activity and abundance were important for most groups, with a marked trough during cool and dry months. The numerical contribution of most arthropod guilds to the arboreal community was not constant throughout the year.
• 5 Seasonal changes in the species composition of the arboreal community appeared not as a succession of well-defined subcommunities throughout the year, but as a continuum of species of extended seasonal ranges.
• 6 This subtropical insect-plant system presented several phenological features which were classified under tropical and temperate characteristics. This partition is open to discussion.

     

Parasites within the new phylogeny of eukaryotes

In the past few years, molecular phylogenetic and cladistic analyses of the interrelationships of the living phyla have resulted in a radical reorganization of eukaryote groups. This reorganization has significance for parasitologists, in that it places as sister taxa some of the more speciose and highly parasitic phyla (nematodes and insects), reorganizes what is now recognized as paraphyletic sets of 'wormy taxa' as the Aschelmintha, and draws numerous bridges between different realms (plants, fungi and animals). This review attempts to explore the role of parasites within the phylogeny of eukaryotes. Extant described parasitic organisms are less common among the eukaryotes than is commonly admitted in the literature.     

On the phylogeny of families and genera within the Temnocephalida

Temnocephalida includes species demonstrating many intermediate steps presenting the transition from commensalism to parasitism. Dramatic morphological changes also occurred within this group but the number of supraspecific taxa is small, making the Temnocephalida an excellent model for evolutionary studies. Having summarised original and relevant published morphological data, we suggest a cladogram (phylogenetic tree) which nearly fully resolves the order of branching of families and main genera within the Temnocephalida. We also introduce a new family, the Diceratocephalidae nov. fam. This revised version was published online in July 2006 with corrections to the Cover Date.     

The phylogeny of proteobacteria: relationships to other eubacterial phyla and eukaryotes

The evolutionary relationships of proteobacteria, which comprise the largest and phenotypically most diverse division among prokaryotes, are examined based on the analyses of available molecular sequence data. Sequence alignments of different proteins have led to the identification of numerous conserved inserts and deletions (referred to as signature sequences), which either are unique characteristics of various proteobacterial species or are shared by only members from certain subdivisions of proteobacteria. These signature sequences provide molecular means to define the proteobacterial phyla and their various subdivisions and to understand their evolutionary relationships to the other groups of eubacteria as well as the eukaryotes. Based on signature sequences that are present in different proteins it is now possible to infer that the various eubacterial phyla evolved from a common ancestor in the following order: low-G+C Gram-positive-->high-G+C Gram-positive-->Deinococcus-Thermus (green nonsulfur bacteria)-->cyanobacteria-->Spirochetes-->Chlamydia-Cytophaga-Aquifex -green sulfur bacteria-->Proteobacteria-1 (epsilon and delta)-->Proteobacteria-2 (alpha)-->Proteobacteria-3 (beta)-->Proteobacteria-4 (gamma). An unexpected but important aspect of the relationship deduced here is that the main eubacterial phyla are related to each other linearly rather than in a tree-like manner, suggesting that the major evolutionary changes within Bacteria have taken place in a directional manner. The identified signatures permit placement of prokaryotes into different groups/divisions and could be used for determinative purposes. These signatures generally support the origin of mitochondria from an alpha-proteobacterium and provide evidence that the nuclear cytosolic homologs of many genes are also derived from proteobacteria.     

Early phylogeny of crinoids within the pelmatozoan clade

Phylogenetic relationships among early crinoids are evaluated by maximizing parsimonious‐informative characters that are unordered and unweighted. Primarily Tremadocian–Darriwilian (Early–Middle Ordovician) taxa are analysed. Stratigraphic congruence metrics support the best phylogenetic hypothesis derived using parsimony methods. This study confirms the traditionally recognized lineages of Palaeozoic crinoids and provides new information on the branching order of evolving lineages. Camerates are basal crinoids with progressively more tipward groups (from an Ordovician perspective) being protocrinoids, cladids (paraphyletic), hybocrinids and disparids. The Protocrinoida should be maintained, but the Aethocrinida should be placed within the Cladida. The results of this study identify phylogenetic structure amongst the major early crinoid lineages and delineate the relative positions of crinoid higher taxa along a tree. Each valid higher taxon discussed herein requires a comprehensive treatment to delimit within‐lineage phylogenetic relationships.     

The internal phylogeny of ants (Hymenoptera: Formicidae)

Abstract. The higher phylogeny of the Formicidae was analysed using 68 characters and 19 taxa: the 14 currently recognized ant subfamilies plus 5 potentially critical infrasubfamilial taxa. The results justified the recognition of 3 additional subfamilies: Aenictogitoninae Ashmead (new status), Apomyrminae Dlussky & Fedoseeva (new status), and Leptanilloidinae Bolton (new subfamily). A second analysis on these better delimited 17 subfamilies resulted in 24 equally most parsimonious trees. All trees showed a basal division of extant Formicidae into two groups, the first containing (Myrmicinae, Pseudomyrmecinae, Nothomyrmeciinae, Myrmeciinae, Formicinae, Dolichoderinae, Aneuretinae) and the second the remaining subfamilies. Clades appearing within these groups included the Cerapachyinae plus 'army ants', the Nothomyrmeciinae plus Myrmeciinae, the 'formicoid' subfamilies (Aneuretinae + Dolichoderinae + Formicinae), and the Old World army ants (Aenictinae + Aenictogitoninae + Doryline), but relationships within the last two groups were not resolved, and the relative positions of the Apomyrminae, Leptanillinae and Ponerinae remained ambiguous. Moreover, a bootstrap analysis produced a consensus tree in which all branches were represented in proportions much lower than 95%. A reconstruction of the ground plan of the Formicidae indicated that the most specialized of all recent ants are the members of the subfamily Dorylinae and the least specialized ones are the monotypic Apomyrminae.