What does "arboreal locomotion" mean exactly and what are the relationships between "climbing", environment and morphology?

The characteristics of "climbing" in the sense of locomotion or posture on three-dimensional substrates are discussed from a biomechanical viewpoint. For this purpose, the mechanical conditions of the most widely spread modes of locomotion or gaits used in arboreal surroundings are reviewed. This allows precise identification of morphological characteristics of traits that are advantageous, and therefore have a positive selective value. Further, at least some of the environmental and substrate characteristics that need to be present for using a specific gait, are noted. It turns out that the extremity which is placed lower on the substrate, has to carry a higher load. If this extremity is consistently the hindlimb--which actually is the case in primates, because of understandable, though complex reasons--a division of labor is likely to occur between the limbs: the hindlimb becoming stronger and the forelimb weaker, but more versatile. A very specific, and advantageous feature of the primates is their possession of prehensile hands and feet. That means the autopodia are able (1) to produce by themselves, without the aid of body weight, very high frictional resistance, and (2) to transmit tensile forces as well as torsional moments on the substrate. The above-mentioned division of labor between fore- and hindlimbs implies that the former make the first contacts with and explore the properties of parts of the environment. As a next step, prehensile hands on long arms may easily replace length and mobility of the neck in getting hold of food items. So very characteristic traits of human body shape can be derived to a large extent from the necessities of arboreal locomotion: Prehensile hands, long arms, concentration of body weight on the hindlimbs, shortness of the trunk in comparison to limb length.     

What are the most relevant parameters for malnutrition in nursing homes?

Prevention of malnutrition is an important issue among older nursing homes residents. From this perspective it is crucial that malnutrition is detected in an early stage. Hence, parameters and tools are required that are suitable for these institutions. Based on recent publications an assessment has been made to identify which parameters are most relevant in nursing homes. The literature study indicates that a wide scope of parameters exists for screening of malnutrition. Only a limited number has been studied in the elderly. In addition, more complicated parameters and tools have not revealed substantial added value to relatively simple parameters, such as foodrecords, weight loss and Body Mass Index.     

How optimal are the binding energetics of barnase and barstar?

The extracellular ribonuclease barnase and its intracellular inhibitor barstar bind fast and with high affinity. Although extensive experimental and theoretical studies have been carried out on this system, it is unclear what the relative importance of different contributions to the high affinity is and whether binding can be improved through point mutations. In this work, we first applied Poisson-Boltzmann electrostatic calculations to 65 barnase-barstar complexes with mutations in both barnase and barstar. The continuum electrostatic calculations with a van der Waals surface dielectric boundary definition result in the electrostatic interaction free energy providing the dominant contribution favoring barnase-barstar binding. The results show that the computed electrostatic binding free energy can be improved through mutations at W44/barstar and E73/barnase. Furthermore, the determinants of binding affinity were quantified by applying COMparative BINding Energy (COMBINE) analysis to derive quantitative structure-activity relationships (QSARs) for the 65 complexes. The COMBINE QSAR model highlights approximately 20 interfacial residue pairs as responsible for most of the differences in binding affinity between the mutant complexes, mainly due to electrostatic interactions. Based on the COMBINE model, together with Brownian dynamics simulations to compute diffusional association rate constants, several mutants were designed to have higher binding affinities than the wild-type proteins.     

Why are there so few evolutionary transitions between aquatic and terrestrial ecosystems?

Insects and flowering plants have rarely invaded the sea. Explanations for this have traditionally centered on the unique shortcomings of these groups in the marine environment. We show, however, that transitions among terrestrial, freshwater, and marine environments are infrequent in all major plant and animal clades except tetrapod vertebrates. In general, well-adapted incumbents are at a competitive advantage over would-be invaders from a physically different habitat. Data on the times and places of transition are consistent with our contention that evolutionary transitions among physically different environments are most likely when incumbents in the recipient environment exist in a regime of low-intensity competition and prcdation, as in terrestrial communities of the middle Paleozoic or the land biotas of oceanic islands. Freshwater environments, in which inferred intensities of predation are lower than in most marine and terrestrial environments, offer less biotic resistance to invaders than do communities in the sea or on land. Most invaders respond to novel physical circumstances by shutting down their metabolic machinery, and therefore add to their subordinate status as competitors with active incumbents. Only active tetrapods, particularly those with high and endothermically driven rates of metabolism, have successfully overcome this limitation.     

Unifying principles in terrestrial locomotion: do hopping Australian marsupials fit in?

Mammalian terrestrial locomotion has many unifying principles. However, the Macropodoidea are a particularly interesting group that exhibit a number of significant deviations from the principles that seem to apply to other mammals. While the properties of materials that comprise the musculoskeletal system of mammals are similar, evidence suggests that tendon properties in macropodoid marsupials may be size or function dependent, in contrast to the situation in placental mammals. Postural differences related to hopping versus running have a dramatic effect on the scaling of the pelvic limb musculoskeletal system. Ratios of muscle fibre to tendon cross-sectional areas for ankle extensors and digital flexors scale with positive allometry in all mammals, but exponents are significantly higher in macropods. Tendon safety factors decline with increasing body mass in mammals, with eutherians at risk of ankle extensor tendon rupture at a body mass of about 150 kg, whereas kangaroos encounter similar problems at a body mass of approximately 35 kg. Tendon strength appears to limit locomotor performance in these animals. Elastic strain energy storage in tendons is mass dependent in all mammals, but exponents are significantly larger in macropodid. Tibial stresses may scale with positive allometry in kangaroos, which result in lower bone safety factors in macropods compared to eutherian mammals.     

Astrocytic energetics during excitatory neurotransmission: What are contributions of glutamate oxidation and glycolysis?

Astrocytic energetics of excitatory neurotransmission is controversial due to discrepant findings in different experimental systems in vitro and in vivo. The energy requirements of glutamate uptake are believed by some researchers to be satisfied by glycolysis coupled with shuttling of lactate to neurons for oxidation. However, astrocytes increase glycogenolysis and oxidative metabolism during sensory stimulation in vivo, indicating that other sources of energy are used by astrocytes during brain activation. Furthermore, glutamate uptake into cultured astrocytes stimulates glutamate oxidation and oxygen consumption, and glutamate maintains respiration as well as glucose. The neurotransmitter pool of glutamate is associated with the faster component of total glutamate turnover in vivo, and use of neurotransmitter glutamate to fuel its own uptake by oxidation-competent perisynaptic processes has two advantages, substrate is supplied concomitant with demand, and glutamate spares glucose for use by neurons and astrocytes. Some, but not all, perisynaptic processes of astrocytes in adult rodent brain contain mitochondria, and oxidation of only a small fraction of the neurotransmitter glutamate taken up into these structures would be sufficient to supply the ATP required for sodium extrusion and conversion of glutamate to glutamine. Glycolysis would, however, be required in perisynaptic processes lacking oxidative capacity. Three lines of evidence indicate that critical cornerstones of the astrocyte-to-neuron lactate shuttle model are not established and normal brain does not need lactate as supplemental fuel: (i) rapid onset of hemodynamic responses to activation delivers oxygen and glucose in excess of demand, (ii) total glucose utilization greatly exceeds glucose oxidation in awake rodents during activation, indicating that the lactate generated is released, not locally oxidized, and (iii) glutamate-induced glycolysis is not a robust phenotype of all astrocyte cultures. Various metabolic pathways, including glutamate oxidation and glycolysis with lactate release, contribute to cellular energy demands of excitatory neurotransmission.     

What are the genuine action potentials in plants?

This is a comment on the paper by Pyatygin in this issue [Biophysics 53(1), 81–86 (2008)], indicating some points that should be clarified to comprehensively assess the apparent diversity of plant electrical signaling.     

What are the relevant parameters for the geometrical optimization of an implantable bioartificial pancreas?

A sphere within a cylinder representing the islet encapsulated in a hollow fiber can model an implantable bioartificial pancreas. Based on a finite element model for insulin response to a glucose load in the presence of various oxygen supplies, the present study aimed at pointing out the major parameters influencing this secretion. The computational results treated with the Taguchi method clearly demonstrated that geometrical parameters (fiber length and islet density) should be precisely optimized for an enhanced insulin response. This requires the collection of more relevant experimental data concerning the islet oxygen consumption. Moreover, the relative errors on glucose consumption or insulin secretion by the islets do not seem to affect the whole optimization process, which should focus on the oxygen supply to islets.     

Ecophysiological traits of terrestrial and aquatic carnivorous plants: are the costs and benefits the same?

Identification of tradeoffs among physiological and morphological traits and their use in cost–benefit models and ecological or evolutionary optimization arguments have been hallmarks of ecological analysis for at least 50 years. Carnivorous plants are model systems for studying a wide range of ecophysiological and ecological processes and the application of a cost–benefit model for the evolution of carnivory by plants has provided many novel insights into trait‐based cost–benefit models. Central to the cost–benefit model for the evolution of botanical carnivory is the relationship between nutrients and photosynthesis; of primary interest is how carnivorous plants efficiently obtain scarce nutrients that are supplied primarily in organic form as prey, digest and mineralize them so that they can be readily used, and allocate them to immediate versus future needs. Most carnivorous plants are terrestrial – they are rooted in sandy or peaty wetland soils – and most studies of cost–benefit tradeoffs in carnivorous plants are based on terrestrial carnivorous plants. However approximately 10% of carnivorous plants are unrooted aquatic plants. Here we ask whether the cost–benefit model applies equally well to aquatic carnivorous plants and what general insights into tradeoff models are gained by this comparison. Nutrient limitation is more pronounced in terrestrial carnivorous plants, which also have much lower growth rates and much higher ratios of dark respiration to photosynthetic rates than aquatic carnivorous plants. Phylogenetic constraints on ecophysiological tradeoffs among carnivorous plants remain unexplored. Despite differences in detail, the general cost–benefit framework continues to be of great utility in understanding the evolutionary ecology of carnivorous plants. We provide a research agenda that if implemented would further our understanding of ecophysiological tradeoffs in carnivorous plants and also would provide broader insights into similarities and differences between aquatic and terrestrial plants of all types.     

Rotifers,cladocerans and planktivorous fish: What are the major interactions?

Results of ten outdoor tank experiments on the effects of two kinds of planktivorous fish (Dorosoma cepedianum and Menidia beryllina) on phytoplankton and zooplankton were reviewed for evidence of rotifer-cladoceran interactions. Correlation and multiple regression analyses of the responses of populations of six rotifer species in ten experiments were examined for evidence of interference competition with daphnids, resource exploitation, or invertebrate predation by crustaceans associated with daphnid-dominated communities. A separate enclosure experiment was conducted to assess the potential for short-term effects of dense daphnid populations on four rotifer populations. Indirect resource-mediated effects on rotifer populations associated with manipulations of planktivorous fish were more numerous and consistently expressed than direct negative effects of cladocerans or copepods on rotifer populations.