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91.
Philipp Wagner Joachim T. Haug Jürgen Sell Carolin Haug 《Pal?ontologische Zeitschrift》2017,91(4):463-472
The tadpole shrimp Triops cancriformis (Branchiopoda, Eucrustacea) is often referred to as a “living fossil.” This term implies that the morphology of a species has barely changed for hundreds of millions of years; in the case of T. cancriformis, for about 200 million years. In 1938, Trusheim documented fossil notostracans from the Upper Triassic of southern Germany (237–200 million years) and named them T. cancriformis minor due to their small size compared to modern forms of T. cancriformis. We compared the ontogenetic sequence of the fossil forms to that of modern forms. Fossil material came from the Museum Terra Triassic in Euerdorf and originated from the same geological formation (the Hassberge Formation) as the Trusheim material, which is considered to be nearly entirely lost. The specimens were documented using cross-polarized light and processed into high-resolution images. Fluorescence microscopy was used to document exuviae and carcasses of extant representatives of T. cancriformis. Both forms showed an elongation and similar trends in the length/width ratio of the shield during ontogeny. However, differences were found in the starting point of the developmental processes. Fossil forms start out with a more roundly shaped shield, which becomes more elliptical, while extant forms already start with a more elliptical shield shape. Further differences between extant and fossil forms were found upon comparing shield to trunk ratios. All differences are highly significant statistically. These differences in ontogeny cast severe doubt on the interpretation that T. cancriformis has been static for 237 million years. While the term “living fossil” is misleading and its use should be discouraged in general, it seems to be especially inappropriate to apply it to T. cancriformis. 相似文献
92.
Cerium Oxide Decorated Polymer Nanofibers as Effective Membrane Reinforcement for Durable,High‐Performance Fuel Cells
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Matthias Breitwieser Carolin Klose Armin Hartmann Andreas Büchler Matthias Klingele Severin Vierrath Roland Zengerle Simon Thiele 《Liver Transplantation》2017,7(6)
High‐power, durable composite fuel cell membranes are fabricated here by direct membrane deposition (DMD). Poly(vinylidene fluoride‐co ‐hexafluoropropylene) (PVDF‐HFP) nanofibers, decorated with CeO2 nanoparticles are directly electrospun onto gas diffusion electrodes. The nanofiber mesh is impregnated by inkjet‐printed Nafion ionomer dispersion. This results in 12 µm thin multicomponent composite membranes. The nanofibers provide membrane reinforcement, whereas the attached CeO2 nanoparticles promote improved chemical membrane durability due to their radical scavenging properties. In a 100 h accelerated stress test under hot and dry conditions, the reinforced DMD fuel cell shows a more than three times lower voltage decay rate (0.39 mV h?1) compared to a comparably thin Gore membrane (1.36 mV h?1). The maximum power density of the DMD fuel cell drops by 9%, compared to 54% measured for the reference. Impedance spectroscopy reveals that ionic and mass transport resistance of the DMD fuel cell are unaffected by the accelerated stress test. This is in contrast to the reference, where a 90% increase of the mass transport resistance is measured. Energy dispersive X‐ray spectroscopy reveals that no significant migration of cerium into the catalyst layers occurs during degradation. This proves that the PVDF‐HFP backbone provides strong anchoring of CeO2 in the membrane. 相似文献
93.
Little association of biological trait values with environmental variables in invasive alien round goby (Neogobius melanostomus)
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Alexander F. Cerwenka Alfredo Pagnotta Carolin Böker Joerg Brandner Juergen Geist Ulrich K. Schliewen 《Ecology and evolution》2017,7(12):4076-4085
The relative importance of species‐specific biological trait characteristics and environmental factors in invasions of nonindigenous species remains controversial because both have mostly been studied independently. Thus, the main objective of this study was to examine the correlation of biological traits with environmental variation in the globally invasive round goby Neogobius melanostomus from the upper Danube River. Based on a sample of 653 specimens along a continuous 200 km river pathway, links between nine environmental factors (substrate‐type, six water measurements, and the communities of fishes and macroinvertebrates) and seven biological traits (nutritional and energetic status, trade‐offs of parasite resistance and resource allocation, and three growth proxies) were analyzed. Biological trait values of N. melanostomus hardly correlated with the environment, could not explain invasion progress and imply a general low overall importance for invasion success. Instead, alternative individual life‐history trajectories appear to determine invasion success. This is in line with up to 15% of all specimens having outlying biological trait values of potential adaptive value, suggesting a considerable importance of adaptive trait variation among single individuals for the whole invasion progress. This “individual trait utility hypothesis” gives an alternative explanation for success of invasive species by single individuals carrying particular traits, and it should be specifically targeted and analyzed at currently invaded sites. 相似文献
94.
In boreal spruce forests that rarely experience extensive disturbances, fine-scale vegetation gaps are important for succession
dynamics and species diversity. We examined the community implications of fine-scale gap disturbances by selective removal
of vegetation layers in a pristine boreal spruce forest in Northern Finland. The aim was to investigate how the speed of recovery
depends on the type of disturbance and the species growth form. We also wanted to know if there appeared changes in species
composition after disturbance. Five different treatments were applied in the study: Control, removal of the ground layer (bryophytes
and lichens), removal of the understorey layer (dwarf shrubs, herbs and graminoids), removal of both the ground and understorey
layers, and complete removal of the vegetation and humus layers above the mineral soil. The vegetation recovery was monitored
in terms of cover and species numbers over a 5-year period. Understorey layer cover, composed mainly of clonal dwarf shrubs,
recovered completely in 4 years in treatments where the humus layer remained intact, whereas ground layer cover did not reach
the control level in plots from where bryophytes and lichens were removed. Recovery was faster in terms of species number
than species cover. Bryophytes, graminoids and dominant dwarf shrubs appeared in all disturbed plots quickly after disturbance.
Seedlings of trees appeared exclusively in disturbed plots. Graminoids dominated after the removal of humus layer. The results
indicate that the regeneration of forest floor after small gap disturbance occurs mainly by re-establishment of the dominant
species. Although destruction of the humus layer leaves a long-lasting scar to the forest floor, exposing of mineral soil
may enhance the sexual reproduction of dominant species and the colonization of weaker competitors. 相似文献
95.
Michela Baccini Eva-Maria Bachmaier Annibale Biggeri Mark V. Boekschoten Freek G. Bouwman Lorraine Brennan Robert Caesar Saverio Cinti Susan L. Coort Katie Crosley Hannelore Daniel Christian A. Drevon Susan Duthie Lars Eijssen Ruan M. Elliott Marjan van Erk Chris Evelo Mike Gibney Carolin Heim Graham W. Horgan Ian T. Johnson Thomas Kelder Robert Kleemann Teake Kooistra Martijn P. van Iersel Edwin C. Mariman Claus Mayer Gerard McLoughlin Michael Müller Francis Mulholland Ben van Ommen Abigael C. Polley Estelle Pujos-Guillot Isabel Rubio-Aliaga Helen M. Roche Baukje de Roos Manuela Sailer Giulia Tonini Lynda M. Williams Nicole de Wit 《Genes & nutrition》2008,3(3-4):147-151
96.
Diversifying selection and concerted evolution of a type IV secretion system in Bartonella 总被引:2,自引:0,他引:2
We have studied the evolution of a type IV secretion system (T4SS), in Bartonella, which is thought to have changed function from conjugation to erythrocyte adherence following a recent horizontal gene transfer event. The system, called Trw, is unique among T4SSs in that genes encoding both exo- and intracellular components are located within the same duplicated fragment. This provides an opportunity to study the influence of selection on proteins involved in host-pathogen interactions. We sequenced the trw locus from several strains of Bartonella henselae and investigated its evolutionary history by comparisons to other Bartonella species. Several instances of recombination and gene conversion events where detected in the 2- to 5-fold duplicated gene fragments encompassing trwJIH, explaining the homogenization of the anchoring protein TrwI and the divergence of the minor pilus protein TrwJ. A phylogenetic analysis of the 7- to 8-fold duplicated gene coding for the major pilus protein TrwL displayed 2 distinct clades, likely representing a subfunctionalization event. The analyses of the B. henselae strains also identified a recent horizontal transfer event of almost the complete trwL region. We suggest that the switch in function of the T4SS was mediated by the duplication of the genes encoding pilus components and their diversification by combinatorial sequence shuffling within and among genomes. We suggest that the pilus proteins have evolved by diversifying selection to match a divergent set of erythrocyte surface structures, consistent with the trench warfare coevolutionary model. 相似文献
97.
Lenman M Sörensson C Andreasson E 《Molecular plant-microbe interactions : MPMI》2008,21(10):1275-1284
Protein phosphorylation is a key biological process that regulates reactions involved in plant-microbe interactions. The phosphorylated form of a protein often represents only a small fraction of the total population and can be problematic to analyze in a mass spectrometer. We demonstrate how a titanium dioxide (TiO(2)) resin can be employed for the enrichment of phosphoproteins, as well as a method to derivatize TiO(2)-purified phosphopeptides to facilitate determination of the exact site of phosphorylation. The use of these methods was exemplified by the identification of two plant proteins that were shown to be phosphorylated after the elicitation of Arabidopsis cells with Phytophthora infestans zoospores and xylanase. Both of the proteins that were identified, At5g54430.1 and At4g27320.1, were found to contain a universal stress protein domain with conserved residues for ATP binding. 相似文献
98.
This review is motivated by the true explosion in the number of recent studies both developing and ameliorating probabilistic models of codon evolution. Traditionally parametric, the first codon models focused on estimating the effects of selective pressure on the protein via an explicit parameter in the maximum likelihood framework. Likelihood ratio tests of nested codon models armed the biologists with powerful tools, which provided unambiguous evidence for positive selection in real data. This, in turn, triggered a new wave of methodological developments. The new generation of models views the codon evolution process in a more sophisticated way, relaxing several mathematical assumptions. These models make a greater use of physicochemical amino acid properties, genetic code machinery, and the large amounts of data from the public domain. The overview of the most recent advances on modeling codon evolution is presented here, and a wide range of their applications to real data is discussed. On the downside, availability of a large variety of models, each accounting for various biological factors, increases the margin for misinterpretation; the biological meaning of certain parameters may vary among models, and model selection procedures also deserve greater attention. Solid understanding of the modeling assumptions and their applicability is essential for successful statistical data analysis. 相似文献
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