Common design in a unique midline neuropil in the brains of arthropods

Most insects possess an assemblage of midline neuropils in their protocerebrum called the central complex. Recent studies have identified comparable assemblages in the malacostracan protocerebrum. Studies of Drosophila melanogaster locomotory mutants suggest that in insects one role for the central complex might be to orchestrate limb actions. This is anecdotally supported by comparisons amongst insects suggesting that elaboration of central complex architecture correlates with complexity of limb motor repertoires. The present account describes immunocytochemical and neuroanatomical observations that reveal common design principles amongst midline neuropils in four arthropod clades, the hexapods, crustaceans, chilopods, and chelicerates and the absence of midline neuropils in diplopods. The chilopod midline neuropil, which is columnar and stratified and lacks chiasmal axons to the dorsal protocerebrum or connections to discrete satellite regions, may represent the plesiomorphous condition. The complete absence of a midline neuropil in diplopods supports previous neuroanatomical studies suggesting that the 'Myriapoda' are an artificial paraphyletic group. The columnar and layered arcuate midline neuropils of chelicerates are compared with columnar and layered midline neuropils of chilopods. No midline neuropil has been identified in a lophotrochozoan outgroup, the Polychaeta.     

Evolution of the central complex in the arthropod brain with respect to the visual system

Modular midline neuropils, termed arcuate body (Chelicerata, Onychophora) or central body (Myriapoda, Crustacea, Insecta), are a prominent feature of the arthropod brain. In insects and crayfish, the central body is connected to a second midline-spanning neuropil, the protocerebral bridge. Both structures are collectively termed central complex. While some investigators have assumed that central and arcuate bodies are homologous, others have questioned this view. Stimulated by recent evidence for a role of the central complex in polarization vision and object recognition, the architectures of midline neuropils and their associations with the visual system were compared across panarthropods. In chelicerates and onychophorans, second-order neuropils subserving the median eyes are associated with the arcuate body. The central complex of decapods and insects, instead, receives indirect input from the lateral (compound) eye visual system, and connections with median eye (ocellar) projections are present. Together with other characters these data are consistent with a common origin of arcuate bodies and central complexes from an ancestral modular midline neuropil but, depending on the choice of characters, the protocerebral bridge or the central body shows closer affinity with the arcuate body. A possible common role of midline neuropils in azimuth-dependent sensory and motor tasks is discussed.     

Comparative neuroanatomy suggests repeated reduction of neuroarchitectural complexity in Annelida

Background

Paired mushroom bodies, an unpaired central complex, and bilaterally arranged clusters of olfactory glomeruli are among the most distinctive components of arthropod neuroarchitecture. Mushroom body neuropils, unpaired midline neuropils, and olfactory glomeruli also occur in the brains of some polychaete annelids, showing varying degrees of morphological similarity to their arthropod counterparts. Attempts to elucidate the evolutionary origin of these neuropils and to deduce an ancestral ground pattern of annelid cerebral complexity are impeded by the incomplete knowledge of annelid phylogeny and by a lack of comparative neuroanatomical data for this group. The present account aims to provide new morphological data for a broad range of annelid taxa in order to trace the occurrence and variability of higher brain centers in segmented worms.

Results

Immunohistochemically stained preparations provide comparative neuroanatomical data for representatives from 22 annelid species. The most prominent neuropil structures to be encountered in the annelid brain are the paired mushroom bodies that occur in a number of polychaete taxa. Mushroom bodies can in some cases be demonstrated to be closely associated with clusters of spheroid neuropils reminiscent of arthropod olfactory glomeruli. Less distinctive subcompartments of the annelid brain are unpaired midline neuropils that bear a remote resemblance to similar components in the arthropod brain. The occurrence of higher brain centers such as mushroom bodies, olfactory glomeruli, and unpaired midline neuropils seems to be restricted to errant polychaetes.

Conclusions

The implications of an assumed homology between annelid and arthropod mushroom bodies are discussed in light of the 'new animal phylogeny'. It is concluded that the apparent homology of mushroom bodies in distantly related groups has to be interpreted as a plesiomorphy, pointing towards a considerably complex neuroarchitecture inherited from the last common ancestor, Urbilateria. Within the annelid radiation, the lack of mushroom bodies in certain groups is explained by widespread secondary reductions owing to selective pressures unfavorable for the differentiation of elaborate brains. Evolutionary pathways of mushroom body neuropils in errant polychaetes remain enigmatic.     

The organization and evolutionary implications of neuropils and their neurons in the brain of the onychophoran Euperipatoides rowelli

This account describes the organization of the brain of the adult Euperipatoides rowelli, a member of the Onychophora or "velvet worms." The present account identifies three cerebral divisions, the first of which contains primary olfactory neuropils, visual neuropils, and brain regions that correspond anatomically to the mushroom bodies of annelids, chelicerates, myriapods, and insects. In common with the brains of many chelicerates, the onychophoran brain is supplied by many thousands of uniformly small basophilic perikarya. Other chelicerate-like features include mushroom body lobes that extend across the brain's midline, an unpaired arch-shaped midline neuropil, and visual pathways that supply midline neuropil and that of the mushroom bodies. These and other similarities with chelicerate brains are discussed in the context of arthropod evolution and with reference to recent molecular phylogenies.     

Wiring a periscope--ocelli, retinula axons, visual neuropils and the ancestrality of sea spiders

The Pycnogonida or sea spiders are cryptic, eight-legged arthropods with four median ocelli in a ‘periscope’ or eye tubercle. In older attempts at reconstructing phylogeny they were Arthropoda incertae sedis, but recent molecular trees placed them as the sister group either to all other euchelicerates or even to all euarthropods. Thus, pycnogonids are among the oldest extant arthropods and hold a key position for the understanding of arthropod evolution. This has stimulated studies of new sets of characters conductive to cladistic analyses, e.g. of the chelifores and of the hox gene expression pattern. In contrast knowledge of the architecture of the visual system is cursory. A few studies have analysed the ocelli and the uncommon “pseudoinverted” retinula cells. Moreover, analyses of visual neuropils are still at the stage of Hanström''s early comprehensive works. We have therefore used various techniques to analyse the visual fibre pathways and the structure of their interrelated neuropils in several species. We found that pycnogonid ocelli are innervated to first and second visual neuropils in close vicinity to an unpaired midline neuropil, i.e. possibly the arcuate body, in a way very similar to ancestral euarthropods like Euperipatoides rowelli (Onychophora) and Limulus polyphemus (Xiphosura). This supports the ancestrality of pycnogonids and sheds light on what eyes in the pycnogonid ground plan might have ‘looked’ like. Recently it was suggested that arthropod eyes originated from simple ocelli similar to larval eyes. Hence, pycnogonid eyes would be one of the early offshoots among the wealth of more sophisticated arthropod eyes.     

The synganglion of the jumping spider Marpissa muscosa (Arachnida: Salticidae): Insights from histology,immunohistochemistry and microCT analysis

Jumping spiders are known for their extraordinary cognitive abilities. The underlying nervous system structures, however, are largely unknown. Here, we explore and describe the anatomy of the brain in the jumping spider Marpissa muscosa (Clerck, 1757) by means of paraffin histology, X-ray microCT analysis and immunohistochemistry as well as three-dimensional reconstruction. In the prosoma, the CNS is a clearly demarcated mass that surrounds the esophagus. The anteriormost neuromere, the protocerebrum, comprises nine bilaterally paired neuropils, including the mushroom bodies and one unpaired midline neuropil, the arcuate body. Further ventrally, the synganglion comprises the cheliceral (deutocerebrum) and pedipalpal neuropils (tritocerebrum). Synapsin-immunoreactivity in all neuropils is generally strong, while allatostatin-immunoreactivity is mostly present in association with the arcuate body and the stomodeal bridge. The most prominent neuropils in the spider brain, the mushroom bodies and the arcuate body, were suggested to be higher integrating centers of the arthropod brain. The mushroom body in M. muscosa is connected to first and second order visual neuropils of the lateral eyes, and the arcuate body to the second order neuropils of the anterior median eyes (primary eyes) through a visual tract. The connection of both, visual neuropils and eyes and arcuate body, as well as their large size corroborates the hypothesis that these neuropils play an important role in cognition and locomotion control of jumping spiders. In addition, we show that the architecture of the brain of M. muscosa and some previously investigated salticids differs significantly from that of the wandering spider Cupiennius salei, especially with regard to structure and arrangement of visual neuropils and mushroom body. Thus, we need to explore the anatomical conformities and specificities of the brains of different spider taxa in order to understand evolutionary transformations of the arthropod brain.     

Three-dimensional reconstruction of mushroom body neuropils in the polychaete species <Emphasis Type="Italic">Nereis diversicolor</Emphasis> and <Emphasis Type="Italic">Harmothoe areolata</Emphasis> (Phyllodocida,Annelida)

Mushroom bodies are prominent brain neuropils present in most arthropod representatives. Similar structures in the brain of certain polychaete species are possibly homologous to these structures. Using three-dimensional reconstruction techniques, we investigated the structural composition of the mushroom body neuropils in the polychaete species Nereis diversicolor and Harmothoe areolata. Comparative analysis revealed a common organization of neuropil substructures in both species that closely matches the basic assembly of arthropod mushroom bodies. Concurring with earlier homology assessments, these neuroarchitectural similarities provide support for a common origin of mushroom body neuropils in polychaetes and arthropods. Beyond that, differences in the morphological differentiation of neuropil substructures indicate polychaete mushroom bodies to show a high degree of morphological variability, thus impeding the quest for a common ground pattern of these brain centers.     

The evolution of crustacean and insect optic lobes and the origins of chiasmata

In malacostracan crustaceans and insects three nested optic lobe neuropils are linked by two successive chiasmata that reverse and then reverse again horizontal rows of retinotopic columns. Entomostracan crustaceans possess but two retinotopic neuropils connected by uncrossed axons: a distal lamina and an inner plate-like neuropil, here termed the visual tectum that is contiguous with the protocerebrum. This account proposes an evolutionary trajectory that explains the origin of chiasmata from an ancestral taxon lacking chiasmata. A central argument employed is that the two optic lobe neuropils of entomostracans are homologous to the lamina and lobula plate of insects and malacostracans, all of which contain circuits for motion detection—an archaic attribute of visual systems. An ancestral duplication of a cell lineage originally providing the entomostracan lamina is proposed to have given rise to an outer and inner plexiform layer. It is suggested that a single evolutionary step resulted in the separation of these layers and, as a consequence, their developmental connection by a chiasma with the inner layer, the malacostracan-insect medulla, still retaining its uncrossed connections to the deep plate-like neuropil. It is postulated that duplication of cell lineages of the inner proliferation zone gave rise to a novel neuropil, the lobula. An explanation for the second chiasma is that it derives from uncrossed axons originally supplying the visual tectum that subsequently supply collaterals to the opposing surface of the newly evolved lobula. A cladistic analysis based on optic lobe anatomy of taxa possessing compound eyes supports a common ancestor of the entomostracans, malacostracan crustaceans, and insects.     

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.     

A congruent solution to arthropod phylogeny: phylogenomics,microRNAs and morphology support monophyletic Mandibulata

While a unique origin of the euarthropods is well established, relationships between the four euarthropod classes—chelicerates, myriapods, crustaceans and hexapods—are less clear. Unsolved questions include the position of myriapods, the monophyletic origin of chelicerates, and the validity of the close relationship of euarthropods to tardigrades and onychophorans. Morphology predicts that myriapods, insects and crustaceans form a monophyletic group, the Mandibulata, which has been contradicted by many molecular studies that support an alternative Myriochelata hypothesis (Myriapoda plus Chelicerata). Because of the conflicting insights from published molecular datasets, evidence from nuclear-coding genes needs corroboration from independent data to define the relationships among major nodes in the euarthropod tree. Here, we address this issue by analysing two independent molecular datasets: a phylogenomic dataset of 198 protein-coding genes including new sequences for myriapods, and novel microRNA complements sampled from all major arthropod lineages. Our phylogenomic analyses strongly support Mandibulata, and show that Myriochelata is a tree-reconstruction artefact caused by saturation and long-branch attraction. The analysis of the microRNA dataset corroborates the Mandibulata, showing that the microRNAs miR-965 and miR-282 are present and expressed in all mandibulate species sampled, but not in the chelicerates. Mandibulata is further supported by the phylogenetic analysis of a comprehensive morphological dataset covering living and fossil arthropods, and including recently proposed, putative apomorphies of Myriochelata. Our phylogenomic analyses also provide strong support for the inclusion of pycnogonids in a monophyletic Chelicerata, a paraphyletic Cycloneuralia, and a common origin of Arthropoda (tardigrades, onychophorans and arthropods), suggesting that previous phylogenies grouping tardigrades and nematodes may also have been subject to tree-reconstruction artefacts.     

Serotonin immunoreactive interneurons in the brain of the Remipedia: new insights into the phylogenetic affinities of an enigmatic crustacean taxon

ABSTRACT: BACKGROUND: Remipedia, a group of homonomously segmented, cave-dwelling, eyeless arthropods have been regarded as basal crustaceans in most early morphological and taxonomic studies. However, molecular sequence information together with the discovery of a highly differentiated brain led to a reconsideration of their phylogenetic position. Various conflicting hypotheses have been proposed including the claim for a basal position of Remipedia up to a close relationship with Malacostraca or Hexapoda. To provide new morphological characters that may allow phylogenetic insights, we have analyzed the architecture of the remipede brain in more detail using immunocytochemistry (serotonin, acetylated alpha-tubulin, synapsin) combined with confocal laser-scanning microscopy and image reconstruction techniques. This approach allows for a comprehensive neuroanatomical comparison with other crustacean and hexapod taxa. RESULTS: The dominant structures of the brain are the deutocerebral olfactory neuropils, which are linked by the olfactory globular tracts to the protocerebral hemiellipsoid bodies. The olfactory globular tracts form a characteristic chiasm in the center of the brain. In Speleonectes tulumensis, each brain hemisphere contains about 120 serotonin immunoreactive neurons, which are distributed in distinct cell groups supplying fine, profusely branching neurites to 16 neuropilar domains. The olfactory neuropil comprises more than 300 spherical olfactory glomeruli arranged in sublobes. Eight serotonin immunoreactive neurons homogeneously innervate the olfactory glomeruli. In the protocerebrum, serotonin immunoreactivity revealed several structures, which, based on their position and connectivity resemble a central complex comprising a central body, a protocerebral bridge, W-, X-, Y-, Z-tracts, and lateral accessory lobes. CONCLUSIONS: The brain of Remipedia shows several plesiomorphic features shared with other Mandibulata, such as deutocerebral olfactory neuropils with a glomerular organization, innervations by serotonin immunoreactive interneurons, and connections to protocerebral neuropils. Also, we provided tentative evidence for W-, X-, Y-, Z-tracts in the remipedian central complex like in the brain of Malacostraca, and Hexapoda. Furthermore, Remipedia display several synapomorphies with Malacostraca supporting a sister group relationship between both taxa. These homologies include a chiasm of the olfactory globular tract, which connects the olfactory neuropils with the lateral protocerebrum and the presence of hemiellipsoid bodies. Even though a growing number of molecular investigations unites Remipedia and Cephalocarida, our neuroanatomical comparison does not provide support for such a sister group relationship.     

Brain organization and the origin of insects: an assessment

Within the Arthropoda, morphologies of neurons, the organization of neurons within neuropils and the occurrence of neuropils can be highly conserved and provide robust characters for phylogenetic analyses. The present paper reviews some features of insect and crustacean brains that speak against an entomostracan origin of the insects, contrary to received opinion. Neural organization in brain centres, comprising olfactory pathways, optic lobes and a central neuropil that is thought to play a cardinal role in multi-joint movement, support affinities between insects and malacostracan crustaceans.     

Serotonin-immunoreactive neurons in scorpion pectine neuropils: similarities to insect and crustacean primary olfactory centres?

The pectines of scorpions are a single pair of mechano- and chemosensory appendages located ventrally behind the most posterior pair of walking legs. They are used for probing the substrate in behaviours such as prey tracking and courtship. The sensory afferents on the pectines supply large segmental neuropils with a conspicuous glomerular structure. The pectine neuropils thus bear similarities to insect and crustacean deutocerebral chemosensory centres associated with the antennae, but they also possess idiosyncratic features. One characteristic property of many insect and decapod crustacean olfactory neuropils is their innervation by single, or very few, large serotonergic (inter-) neurons. This feature, among others, has been proposed to support homology of the olfactory lobes in the two arthropod groups. A possible serotonergic innervation of the scorpion pectine neuropils has not yet been studied, despite its apparent diagnostic and functional importance. We thus examined serotonin-immunoreactivity in the pectine neuropils of Androctonus australis and Pandinus imperator. Both scorpion species yielded similar results. The periphery of the neuropil and the matrix between the glomeruli are supplied by a dense network of serotonin-immunoreactive (5-HT-ir) arborisations and varicosities, while the glomeruli themselves are mostly free of 5-HT-ir fibres. The 5-HT-ir supply of the pectine neuropils has two origins. The first is a pair of neurons on each body side, up to 30 μm in diameter and thus slightly larger than the surrounding somata. These cell bodies are and associated with the neuromeres of the genital and pectine segments. The situation is reminiscent of the 5-HT supply of insect and crustacean olfactory and antennal neuropils. The second 5-HT innervation of the pectine neuropils is from a group of some 10-20 ipsilateral neuronal somata of slightly smaller size (15-20 μm). These are part of a much larger 5-HT-ir group comprising 70-90 somata. The whole group is located more anteriorly than the single soma mentioned above, and associated with the neuromere of the last (4th) walking leg. When compared to data from other arthropods, our findings may suggest that glomerular organisation is an ancestral feature of primary chemosensory centres innervated by arthropod appendages. This idea needs further scrutiny, although supporting evidence may have been overlooked previously, due to the small size of chemosensory neuropils in walking legs and in reduced segmental appendages.     

Persisting stemma neuropils in Chaoborus crystallinus (Diptera: Chaoboridae): Development and evolution of a bipartite visual system

Stemmata or “larval” eyes are of crucial importance for the understanding of the evolution and ontogeny of the hexapod's main visual organs, the compound eyes. Using classical neuroanatomical techniques, I showed that the persisting stemmata of Chaoborus imagos are connected to persisting stemma neuropils neighboring the first and second order neuropils of the compound eyes, and therefore also the imago possesses a stemma lamina and medulla closely associated with the architecture and the developmental pattern of those of the compound eyes. The findings are compared with other arthropods, e.g. accessory lateral eyes in Amandibulata and Myriapoda, suggesting some ancestral rather than derived character states. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

A developmental study of serotonin-immunoreactive neurons in the embryonic brain of the Marbled Crayfish and the Migratory Locust: Evidence for a homologous protocerebral group of neurons

It is well established that the brains of adult malacostracan crustaceans and winged insects display distinct homologies down to the level of single neuropils such as the central complex and the optic neuropils. We wanted to know if developing insect and crustacean brains also share similarities and therefore have explored how neurotransmitter systems arise during arthropod embryogenesis. Previously, Sintoni et al. (2007) had already reported a homology of an individually identified cluster of neurons in the embryonic crayfish and insect brain, the secondary head spot cells that express the Engrailed protein. In the present study, we have documented the ontogeny of the serotonergic system in embryonic brains of the Marbled Crayfish in comparison to Migratory Locust embryos using immunohistochemical methods combined with confocal laser-scan microscopy. In both species, we found a cluster of early emerging serotonin-immunoreactive neurons in the protocerebrum with neurites that cross to the contralateral brain hemisphere in a characteristic commissure suggesting a homology of this cell cluster. Our study is a first step towards a phylogenetic analysis of neurotransmitter system development and shows that, as for the ventral nerve cord, traits related to neurogenesis in the brain can provide valuable hints for resolving the much debated question of arthropod phylogeny.     

Mechanisms of eye development and evolution of the arthropod visual system: The lateral eyes of myriapoda are not modified insect ommatidia

The lateral eyes of Crustacea and Insecta consist of many single optical units, the ommatidia, that are composed of a small, strictly determined and evolutionarily conserved set of cells. In contrast, the eyes of Myriapoda (millipedes and centipedes) are fields of optical units, the lateral ocelli, each of which is composed of up to several hundreds of cells. For many years these striking differences between the lateral eyes of Crustacea/Insecta versus Myriapoda have puzzled evolutionary biologists, as the Myriapoda are traditionally considered to be closely related to the Insecta. The prevailing hypothesis to explain this paradox has been that the myriapod fields of lateral ocelli derive from insect compound eyes by disintegration of the latter into single ommatidia and subsequent fusion of several ommatidia to form multicellular ocelli. To provide a fresh view on this problem, we counted and mapped the arrangement of ocelli during postembryonic development of a diplopod. Furthermore, the arrangement of proliferating cells in the eyes of another diplopod and two chilopods was monitored by labelling with the mitosis marker bromodeoxyuridine. Our results confirm that during eye growth in Myriapoda new elements are added to the side of the eye field, which extend the rows of earlier-generated optical units. This pattern closely resembles that in horseshoe crabs (Chelicerata) and Trilobita. We conclude that the trilobite, xiphosuran, diplopod and chilopod mechanism of eye growth represents the ancestral euarthropod mode of visual-system formation, which raises the possibility that the eyes of Diplopoda and Chilopoda may not be secondarily reconstructed insect eyes.     

Postembryonic development of astrocyte-like glia of the central complex in the grasshopper Schistocerca gregaria

Central complex modules in the postembryonic brain of the grasshopper Schistocerca gregaria are enveloped by Repo-positive/glutamine-synthetase-positive astrocyte-like glia. Such cells constitute Rind-Neuropil Interface glia. We have investigated the postembryonic development of these glia and their anatomical relationship to axons originating from the w, x, y, z tract system of the pars intercerebralis. Based on glutamine synthetase immunolabeling, we have identified four morphological types of cells: bipolar type 1 glia delimit the central body but only innervate its neuropil superficially; monopolar type 2 glia have a more columnar morphology and direct numerous gliopodia into the neuropil where they arborize extensively; monopolar type 3 glia are found predominantly in the region between the noduli and the central body and have a dendritic morphology and their gliopodia project deeply into the central body neuropil where they arborize extensively; multipolar type 4 glia link the central body neuropil with neighboring neuropils of the protocerebrum. These glia occupy type-specific distributions around the central body. Their gliopodia develop late in embryogenesis, elongate and generally become denser during subsequent postembryonic development. Gliopodia from putatively type 3 glia within the central body have been shown to lie closely apposed to individual axons of identified columnar fiber bundles from the w, x, y, z tract system of the central complex. This anatomical association might offer a substrate for neuron/glia interactions mediating postembryonic maturation of the central complex.     

Myriapod monophyly and relationships among myriapod classes based on nearly complete 28S and 18S rDNA sequences

Myriapods play a pivotal position in the arthropod phylogenetic tree. The monophyly of Myriapoda and its internal relationships have been difficult to resolve. This study combined nearly complete 28S and 18S ribosomal RNA gene sequences (3,826 nt in total) to estimate the phylogenetic position of Myriapoda and phylogenetic relationships among four myriapod classes. Our data set consists of six new myriapod sequences and homologous sequences for 18 additional species available in GenBank. Among the six new myriapod sequences, those of the one pauropod and two symphylans are very important additions because they were such difficult taxa to classify in past molecular-phylogenetic studies. Phylogenetic trees were constructed with maximum parsimony, maximum likelihood, and Bayesian analyses. All methods yielded moderate to strong support for the monophyly of Myriapoda. Symphyla grouped strongly with Pauropoda under all analytical conditions. The KH test rejected the traditional view of Dignatha and Progoneata, and the topology obtained here, though not significantly supported, was Diplopoda versus ((Symphyla + Pauropoda) + Chilopoda).     

Invertebrate activity under snow in deciduous woods

Pitfall traps caught large numbers of representatives of 44 families of invertebrates just before snow fall and under the snow. Some groups of ectotherms were most active in late autumn and late winter, the activity of some increased throughout the winter and some showed no major change although subnivean temperatures were usually near 0°C. The most commonly trapped groups were: phalangids, collembolans, diplopods, coleopterans, dipterans, arachnids, gastropods and chilopods.