Macroinvertebrate communities of non-glacial high altitude intermittent streams

1. Macroinvertebrate assemblages of five non‐glacial intermittent high altitude headwater streams (above 1400 m – Serra da Estrela, Portugal), with dry periods of different lengths (0–3 months), were investigated in nearly undisturbed conditions to (i) examine spatial differences and identify environmental variables responsible for the observed invertebrate patterns, (ii) assess the association of dry period length with invertebrate community structure and (iii) determine the influence of using different taxonomic identification levels (order, family and genus) to assess invertebrate community patterns. 2. More than 100 macroinvertebrate genera were identified. Insects clearly dominated these communities with more than 95% of total captures and around 95% of the total richness. Diptera were the most rich and abundant group with chironomid occurrences comprising over 70% of macroinvertebrate captures. 3. The highest taxon richness, diversity, EPT (Ephemeroptera + Plecoptera + Trichoptera) and OCH (Odonata + Coleoptera + Heteroptera) genus richness, the greatest number of exclusive and characteristic taxa identified by the Indicator Value (IndVal), and a distinct community structure shown by Canonical Correspondence Analyses (CCA), were found in the only stream that was never totally dry, with pools lasting over summer. Environmental gradients that spatially structured the macroinvertebrate communities were always related to flow variations. 4. Over time, the highest abundances found in these systems were also related to flow variations and maximum genus richness occurred in the connected pools or in isolated pools. Streams with longer dry periods presented a distinct recolonization phase, with higher abundance of the stonefly larvae Nemoura sp. and the presence of the chironomid larvae Krenosmittia sp., possibly arriving from the hyporheos. 5. Taxonomic level of invertebrate identification was vital for recognizing the characteristic taxa (IndVal) of streams yet was not critical for identifying streams with the highest macroinvertebrate richness/diversity or structuring environmental gradients. 6. Overall, this study emphasizes the variability of high altitude intermittent streams macroinvertebrate communities, despite spatial proximity. This variability was probably related to flow intermittency and hydrologic permanence, different vegetation covers and riverbed substrata. Consequently, the establishment of reference conditions should involve long‐term data collections and more detailed physical characterization. Also, these findings have significant implications for accurately predicting the ecological consequences of future climate change in high altitude scenarios.     

A forgotten homology supporting the monophyly of Tracheata: The subcoxa of insects and myriapods re-visited

The current discussion about the relationships of higher arthropod taxa has led to a conflict between the traditional Tracheata (=Atelocerata) concept (hexapods united with myriapods), the Tetraconata concept (hexapods united with crustaceans, excluding myriapods), and the Paradoxopoda or Myriochelata concept (myriapods united with cheliceratans), with major contradictions between morphological and molecular data. We have analyzed a character set which apparently has completely vanished from the recent debate, namely the equipment of the trunk pleura of myriapods and insects with a characteristic set of concentric sclerites around the leg base and accompanying muscles. Based on the work of Heymons (1899) these sclerites were thought to be remains of the first appendage article, then denominated “subcoxa”. We have re-visited this old idea and show the arrangement of the much discussed pleural structures by SEM for the first time. Obviously a characteristic pattern of concentric pleural plates around the leg-base is present in all major myriapod taxa, including for the first time evidence for their presence in Progoneata. Because of their equal structure and orientation, the pleural sclerites present in entognathous and ectognathous insects may be derived from the same ground pattern. We conclude that the pleurites of Hexapoda and Myriapoda seem to be homologous structures, and there is evidence that the “subcoxa” of Tracheata is homologous with the coxa of crustaceans. Since no other arthropods show these sclerites, the transformation of the crustacean coxa to the pleural region in myriapods and insects is probably a synapomorphy congruent with the traditional Tracheata-hypothesis. Further investigations of recently published molecular work using the phylogenetic network software SplitsTree V.4 indicate that information content of several data sets is not convincing.     

Elastohydrodynamics of the Eyelid Wiper

This paper presents an elastohydrodynamic model of the human eyelid wiper. Standard lubrication theory is applied to the fluid layer between the eyelid wiper and ocular surface. The role of the lubrication film is to reduce the shear stresses by preventing solid to solid contact between the eyelid wiper and ocular surface. For the lubrication film to be effective, it is required that the orientation of the eyelid wiper changes between the opening and closing phases of a blink. In order to model this, the hydrodynamic model is coupled with an elastic mattress model for the soft tissue of the eyelid wiper and ocular surface. This leads to a one-dimensional non-linear partial differential equation governing the fluid pressure in the lubrication film. In order to solve the differential equation, a loading condition or constraint equation must be specified. The resulting system is then solved numerically. The model allows predictions of the tear film flux from under the upper eyelid, as well as normal and shear stresses acting on the ocular surface. These factors are important in relation to dry eye syndrome, deformation of the cornea and contact lens design. It is found that the pressure and shear stress under the eyelid act across a length of approximately 0.1 mm which is consistent with clinical observations. It order to achieve a flow of tears from under the upper eyelid during a blink, the model requires that the normal force the eyelid applies to the ocular surface during the closing phase of the blink is significantly higher than during the opening phase of the blink. Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users.     

Modeling and Analysis of the Effect of Training on \dot{V}O_{2} Kinetics and Anaerobic Capacity

In this paper, we present an application of a number of tools and concepts for modeling and analyzing raw, unaveraged, and unedited breath-by-breath oxygen uptake data. A method for calculating anaerobic capacity is used together with a model, in the form of a set of coupled nonlinear ordinary differential equations to make predictions of the kinetics, the time to achieve a percentage of a certain constant oxygen demand, and the time limit to exhaustion at intensities other than those in which we have data. Speeded oxygen kinetics and increased time limit to exhaustion are also investigated using the eigenvalues of the fixed points of our model. We also use a way of analyzing the oxygen uptake kinetics using a plot of vs which allows one to observe both the fixed point solutions and also the presence of speeded oxygen kinetics following training. A method of plotting the eigenvalue versus oxygen demand is also used which allows one to observe where the maximum amplitude of the so-called slow component will be and also how training has changed the oxygen uptake kinetics by changing the strength of the attracting fixed point for a particular demand.     

Resetting Behavior in a Model of Bursting in Secretory Pituitary Cells: Distinguishing Plateaus from Pseudo-Plateaus

We study a recently discovered class of models for plateau bursting, inspired by models for endocrine pituitary cells. In contrast to classical models for fold-homoclinic (square-wave) bursting, the spikes of the active phase are not supported by limit cycles of the frozen fast subsystem, but are transient oscillations generated by unstable limit cycles emanating from a subcritical Hopf bifurcation around a stable steady state. Experimental time courses are suggestive of such fold-subHopf models because the spikes tend to be small and variable in amplitude; we call this pseudo-plateau bursting. We show here that distinct properties of the response to attempted resets from the silent phase to the active phase provide a clearer, qualitative criterion for choosing between the two classes of models. The fold-homoclinic class is characterized by induced active phases that increase towards the duration of the unperturbed active phase as resets are delivered later in the silent phase. For the fold-subHopf class of pseudo-plateau bursting, resetting is difficult and succeeds only in limited windows of the silent phase but, paradoxically, can dramatically exceed the native active phase duration. J.V. Stern and H.M. Osinga contributed equally.     

Modeling the spontaneous initiation of the polymerization of methyl methacrylate

The mechanism of the spontaneous initiation of the polymerization of methyl methacrylate (MMA) was investigated theoretically. The six minimum energy paths (MEP) of the possible reactions were calculated using the density functional theory (DFT) in conjunction with the B3LYP functional and 6-31G* basis set. The Diels-Alder initiation mechanism (path (I) and path (II)) with remarkably high energy barriers is not applicable to MMA. Four favorable paths were found (path (III), path (IV), path (V) and path (VI)), which are supporting the Flory mechanism. Path (V) has the lowest active energy. Therefore this path is considered as the main path for the spontaneous polymerization of MMA. Figure The mechanism of the spontaneous initiation of the polymerization of methyl methacrylate (MMA) was investigated theoretically. The six minimum energy paths (MEP) of the possible reactions were calculated using the density functional theory (DFT) in conjunction with the B3LYP functional and 6-31G* basis set.     

Oxidation of diiron and triiron sulfurdithiolato complexes: mimics for the active site of [FeFe]-hydrogenase

The oxidation of the hexacarbonyl(1,3-dithiolato-S,S')diiron complexes 4a-4c with varying amounts of dimethyldioxirane (DMD) was systematically studied. The chemoselectivity of the oxidation products depended upon the substituent R (R=H, Me, 1/2 (CH2)(5)). For R=H, four oxidation products, 6a-6d, have been obtained. In the case of R=Me, three products, 7a-7c, were formed, and for R=1/2 (CH2)(5), only complex 8 was observed. These observations are due to steric and electronic effects caused by the substituent R. Additionally, oxidation of the triiron complex 5 with DMD was performed to yield the products 9a and 9b. X-Ray diffraction analyses were performed for 6a-6d, 7a, and 7c, as well as for 9a and 9b. The electronic properties were determined by density-functional theory (DFT) calculations.