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Segment Number (segment + number)
Selected AbstractsSimple Determination of Segment Numbers for Complex Polymer-Solvent SystemsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 2 2007S. Machefer Abstract A theoretical analysis was made to show that segment numbers for complex polymers can be determined by interpreting pVT data in terms of an appropriate segment-based equation of state (EOS). Typically, experiments at high pressures have to be performed to obtain these data. In this study, pVT-derived properties, such as compressibility and speed of sound, together with isobaric specific volume measurements were used as an alternative data source. Experiments were carried out for polyol/water mixtures of different compositions. Taking account of the polymorphism of water, segment numbers were obtained by a numerical regression analysis. Mixture viscosities were calculated using an approved segment-based mixing rule and were in good agreement with experimental data over the temperature range of interest, indicating the validity of the determined segment numbers. [source] Early development and segment formation in the centipede, Strigamia maritima (Geophilomorpha)EVOLUTION AND DEVELOPMENT, Issue 2 2004Ariel D. Chipman Summary Geophilomorph centipedes exhibit a number of unique characteristics that make them of particular developmental and evolutionary interest. Segment numbers in geophilomorphs are higher than in any other centipedes, ranging from 27 to 191. They may be constant within a species, presenting in extreme form the "counting" problem in development, or they may vary,a situation that provides us with the opportunity to study naturally occurring variation in segment numbers. All their segments are generated during embryogenesis, a situation unlike that in the more basal centipede orders, which generate only a fraction of their 15 trunk segments in the embryo and develop the rest postembryonically. Here we provide a foundation for further developmental studies of the Geophilomorpha, building on the one study that has been conducted to date, on the coastal species Strigamia maritima. Development begins with the migration of nuclei to the surface of the egg, which then condense to form an embryonic rudiment of more than 20,000 cells, covering an entire hemisphere. During early development, the embryo can be divided into two distinct areas: a large terminal disc of apparently undifferentiated tissue and the germ-band, which has a clear anteroposterior axis and differentiated segments. The germ-band forms from the anterior of the terminal disc and extends anteriorly as the disc contracts. New segments are formed at the posterior margin of the germ-band. Once the process of segmentation ends, the germ-band folds and sinks into the yolk. We note that the classic description of centipede development, by Heymons more than a century ago, contains a fundamental error in the identification of the axes and hence in the interpretation of early segmentation. [source] An early temperature-sensitive period for the plasticity of segment number in the centipede Strigamia maritimaEVOLUTION AND DEVELOPMENT, Issue 4 2010Vincent Vedel SUMMARY Geophilomorph centipedes show variation in segment number (a) between closely related species and (b) within and between populations of the same species. We have previously shown for a Scottish population of the coastal centipede Strigamia maritima that the temperature of embryonic development is one of the factors that affects the segment number of hatchlings, and hence of adults, as these animals grow epimorphically,that is, without postembryonic addition of segments. Here, we show, using temperature-shift experiments, that the main developmental period during which embryos are sensitive to environmental temperature is surprisingly early, during blastoderm formation and before, or very shortly after, the onset of segmentation. [source] Temperature-dependent plasticity of segment number in an arthropod species: the centipede Strigamia maritimaEVOLUTION AND DEVELOPMENT, Issue 4 2008Vincent Vedel SUMMARY The evolution of arthropod segment number provides us with a paradox, because, whereas there is more than 20-fold variation in this character overall, most classes and orders of arthropods are composed of species that lack any variation in the number of segments. So, what is the origin of the higher-level variation? The centipede order Geophilomorpha is unusual because, with the exception of one of its families, all species exhibit intraspecific variation in segment number. Hence it provides an opportunity to investigate how segment number may change in a microevolutionary context. Here, we show that segment number can be directly altered by an environmental factor (temperature),this is the first such demonstration for any arthropod. The direction of the effect is such that higher temperature during embryogenesis produces more segments. This potentially explains an intraspecific cline in the species concerned, Strigamia maritima, but it does not explain how such a cline is translated into the parallel interspecific pattern of lower-latitude species having more segments. Given the plastic nature of the intraspecific variation, its link with interspecific differences may lie in selection acting on developmental reaction norms. [source] AGGREGATION BEHAVIOUR IN JUVENILE MILLIPEDES FROM THE UPPER CARBONIFEROUS OF MAZON CREEK, ILLINOISPALAEONTOLOGY, Issue 4 2006HEATHER M. WILSON Abstract:, Two ironstone nodules are described from the Braidwood Biota of the Upper Carboniferous Mazon Creek Lagerstätte, Illinois, each preserving numerous juvenile millipedes referred to Euphoberia sp. The millipedes belong to different stadia, as evidenced by segment number, but are similar in size so probably nearly the same age. These juvenile euphoberiids differ from adults in having shorter pleurotergal spines, a reduced number of ocelli and a series of reduced, apodous trunk rings posteriorly. These nodules provide the first evidence of aggregation behaviour in Palaeozoic millipedes. Aggregation in juvenile euphoberiids is hypothesized to serve as a defence mechanism, compensating for the reduced length of their pleurotergal spines relative to adults, possibly through a collective chemical defence. [source] Chemotherapy and antiangiogenesis: drug-specific effects on microvessel sproutingAPMIS, Issue 11 2003PER ALBERTSSON Tumors are angiogenesis dependent. Some chemotherapeutics have been shown to be able to suppress angiogenesis and thus tumor growth in vivo at low, well-tolerated doses. Not much is known about the angiogenesis-modulating effects of chemotherapeutics in vivo, however. Microvessel sprouting is inherent to angiogenesis. Using the rat mesentery assay, we studied the effect of cyclophosphamide, doxorubicin and paclitaxel at a low, atoxic dose on the number of sprouts per unit tissue volume (No. SP) and their length (Le. SP) at the edge of the expanding network in VEGF165 -mediated angiogenesis. A single dose of each cytotoxic drug was administered i.v. 7 days before the animals were sacrificed. Cyclophosphamide significantly lengthened the shortest Le. SP and shortened the longest Le. SP, doxorubicin did not significantly affect Le. SP, whereas paclitaxel significantly shortened both the shortest and the longest Le. SP. No correlation was found between the present results and the distinctly drug-specific results of microvessel segment number and length analyzed within central parts of the same expanding network (1). To our knowledge, this is the first quantitative report on the effect of chemotherapy on angiogenesis sprouting in vivo. Collectively, the data suggest that cyclophosphamide, doxorubicin and paclitaxel at a non-toxic dose primarily target different intrinsic components of the angiogenic cascade, leading to distinctly drug-specific effects. [source] A study of the diversity and geographical variation in numbers of leg-bearing segments in centipedes (Chilopoda: Geophilomorpha) in north-western EuropeBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2010STYLIANOS M. SIMAIAKIS Five species of geophilomorphs, Strigamia maritima (Leach, 1817), Geophilus flavus (De Geer, 1778), Geophilus truncorum Bergsøe and Meinert, 1866, Geophilus proximus C. L. Koch, 1847, and Pachymerium ferrugineum (C. L. Koch, 1835), from various sample sites in north-western Europe were examined for numbers of leg-bearing segments. Where data was adequate, mean segment numbers were correlated with latitudinal gradients for each species. Solely in S. maritima and some populations of P. ferrugineum did the results show a highly significant geographic pattern towards more leg-bearing segments in southern populations of both sexes. As concerns G. proximus, we presented for the first time a remarkable geographic shift towards an increased number of pairs of legs in northern populations. Contrary to the conventional geographic pattern, we found that G. flavus and G. truncorum did not exhibit a north,south increase or decrease in segment number. Although there was no general/universal evidence supporting the occurrence of a significant regression slope between mean segment number and latitude/temperature, more information shows that the overall region-to-region segment variation was highly significant in both sexes. In S. maritima and P. ferrugineum mean segment number was correlated with the north,south temperature cline. The same was not observed in G. proximus. Parthenogenesis in G. proximus, and a series of ecological characteristics such as habitat preferences, spatial distribution, and fragmented populations could explain the presence or absence of a geographic patterning of segment number variation along a latitudinal cline. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 899,909. [source] Early development and segment formation in the centipede, Strigamia maritima (Geophilomorpha)EVOLUTION AND DEVELOPMENT, Issue 2 2004Ariel D. Chipman Summary Geophilomorph centipedes exhibit a number of unique characteristics that make them of particular developmental and evolutionary interest. Segment numbers in geophilomorphs are higher than in any other centipedes, ranging from 27 to 191. They may be constant within a species, presenting in extreme form the "counting" problem in development, or they may vary,a situation that provides us with the opportunity to study naturally occurring variation in segment numbers. All their segments are generated during embryogenesis, a situation unlike that in the more basal centipede orders, which generate only a fraction of their 15 trunk segments in the embryo and develop the rest postembryonically. Here we provide a foundation for further developmental studies of the Geophilomorpha, building on the one study that has been conducted to date, on the coastal species Strigamia maritima. Development begins with the migration of nuclei to the surface of the egg, which then condense to form an embryonic rudiment of more than 20,000 cells, covering an entire hemisphere. During early development, the embryo can be divided into two distinct areas: a large terminal disc of apparently undifferentiated tissue and the germ-band, which has a clear anteroposterior axis and differentiated segments. The germ-band forms from the anterior of the terminal disc and extends anteriorly as the disc contracts. New segments are formed at the posterior margin of the germ-band. Once the process of segmentation ends, the germ-band folds and sinks into the yolk. We note that the classic description of centipede development, by Heymons more than a century ago, contains a fundamental error in the identification of the axes and hence in the interpretation of early segmentation. [source] A study of the diversity and geographical variation in numbers of leg-bearing segments in centipedes (Chilopoda: Geophilomorpha) in north-western EuropeBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2010STYLIANOS M. SIMAIAKIS Five species of geophilomorphs, Strigamia maritima (Leach, 1817), Geophilus flavus (De Geer, 1778), Geophilus truncorum Bergsøe and Meinert, 1866, Geophilus proximus C. L. Koch, 1847, and Pachymerium ferrugineum (C. L. Koch, 1835), from various sample sites in north-western Europe were examined for numbers of leg-bearing segments. Where data was adequate, mean segment numbers were correlated with latitudinal gradients for each species. Solely in S. maritima and some populations of P. ferrugineum did the results show a highly significant geographic pattern towards more leg-bearing segments in southern populations of both sexes. As concerns G. proximus, we presented for the first time a remarkable geographic shift towards an increased number of pairs of legs in northern populations. Contrary to the conventional geographic pattern, we found that G. flavus and G. truncorum did not exhibit a north,south increase or decrease in segment number. Although there was no general/universal evidence supporting the occurrence of a significant regression slope between mean segment number and latitude/temperature, more information shows that the overall region-to-region segment variation was highly significant in both sexes. In S. maritima and P. ferrugineum mean segment number was correlated with the north,south temperature cline. The same was not observed in G. proximus. Parthenogenesis in G. proximus, and a series of ecological characteristics such as habitat preferences, spatial distribution, and fragmented populations could explain the presence or absence of a geographic patterning of segment number variation along a latitudinal cline. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 899,909. [source] Simple Determination of Segment Numbers for Complex Polymer-Solvent SystemsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 2 2007S. Machefer Abstract A theoretical analysis was made to show that segment numbers for complex polymers can be determined by interpreting pVT data in terms of an appropriate segment-based equation of state (EOS). Typically, experiments at high pressures have to be performed to obtain these data. In this study, pVT-derived properties, such as compressibility and speed of sound, together with isobaric specific volume measurements were used as an alternative data source. Experiments were carried out for polyol/water mixtures of different compositions. Taking account of the polymorphism of water, segment numbers were obtained by a numerical regression analysis. Mixture viscosities were calculated using an approved segment-based mixing rule and were in good agreement with experimental data over the temperature range of interest, indicating the validity of the determined segment numbers. [source] Phylogeny of Nerillidae (Polychaeta, Annelida) as inferred from combined 18S rDNA and morphological dataCLADISTICS, Issue 2 2005Katrine Worsaae A phylogeny of the meiofaunal polychaete family Nerillidae based on morphological, molecular and combined data is presented here. The data sets comprise nearly complete sequences of 18S rDNA and 40 morphological characters of 17 taxa. Sequences were analyzed simultaneously with the morphological data by direct optimization in the program POY, with a variety of parameter sets (costs of gaps: transversions: transitions). Three outgroups were selected from the major polychaete group Aciculata and one from Scolecida. The 13 nerillid species from 11 genera were monophyletic in all analyses with very high support, and three new apomorphies for Nerillidae are identified. The topology of the ingroup varied according to the various parameter settings. Reducing the number of outgroups to one decreased the variance among the phylogenetic hypotheses. The congruence among these was tested and a parameter set, with equal weights (222) and extension gap weighted 1, yielded minimum incongruence (ILD). Several terminal clades of the combined analysis were highly supported, as well as the position of Leptonerilla prospera as sister terminal to the other nerillids. The evolution of morphological characters such as segment numbers, chaetae, appendages and ciliation are traced and discussed. A regressive pathway within Nerillidae is indicated for several characters, however, generally implying several convergent losses. Numerous genera are shown to require revision. © The Willi Hennig Society 2005. [source] | ||||||||||