Balance control must be rapidly modified to provide stability in the face of environmental challenges. Although changes in reactive balance over repeated perturbations have been observed previously, ...only anticipatory postural adjustments preceding voluntary movements have been studied in the framework of motor adaptation and learning theory. Here, we hypothesized that adaptation occurs in task-level balance control during responses to perturbations due to central changes in the control of both anticipatory and reactive components of balance. Our adaptation paradigm consisted of a Training set of forward support-surface perturbations, a Reversal set of novel countermanding perturbations that reversed direction, and a Washout set identical to the Training set. Adaptation was characterized by a change in a motor variable from the beginning to the end of each set, the presence of aftereffects at the beginning of the Washout set when the novel perturbations were removed, and a return of the variable at the end of the Washout to a level comparable to the end of the Training set. Task-level balance performance was characterized by peak center of mass (CoM) excursion and velocity, which showed adaptive changes with repetitive trials. Only small changes in anticipatory postural control, characterized by body lean and background muscle activity were observed. Adaptation was found in the evoked long-latency muscular response, and also in the sensorimotor transformation mediating that response. Finally, in each set, temporal patterns of muscle activity converged towards an optimum predicted by a trade-off between maximizing motor performance and minimizing muscle activity. Our results suggest that adaptation in balance, as well as other motor tasks, is mediated by altering central sensitivity to perturbations and may be driven by energetic considerations.
Intracellular endosymbiotic bacteria are found in many terrestrial arthropods and have a profound influence on host biology. A basic question about these symbionts is why they infect the hosts that ...they do, but estimating symbiont incidence (the proportion of potential host species that are actually infected) is complicated by dynamic or low prevalence infections. We develop a maximum-likelihood approach to estimating incidence, and testing hypotheses about its variation. We apply our method to a database of screens for bacterial symbionts, containing more than 3600 distinct arthropod species and more than 150 000 individual arthropods. After accounting for sampling bias, we estimate that 52% (CIs: 48–57) of arthropod species are infected with Wolbachia, 24% (CIs: 20–42) with Rickettsia and 13% (CIs: 13–55) with Cardinium. We then show that these differences stem from the significantly reduced incidence of Rickettsia and Cardinium in most hexapod orders, which might be explained by evolutionary differences in the arthropod immune response. Finally, we test the prediction that symbiont incidence should be higher in speciose host clades. But while some groups do show a trend for more infection in species-rich families, the correlations are generally weak and inconsistent. These results argue against a major role for parasitic symbionts in driving arthropod diversification.
This paper addresses the global challenge of greenhouse gas emissions facing the aluminum industry. The demand, production and use of aluminum are increasing and so are the emissions. From bauxite ...mine to aluminum ingot, the total global average emissions vary somewhat in the literature, but most reported values are now between 12 and 17 metric tonnes of CO
2
-equivalents per tonne of aluminum, depending on the various estimates and assumptions made. Two-thirds of these gases are emitted because the electricity used for electrolysis is produced from fossil fuel sources, mainly coal but also natural gas. Reduction of these emissions is now the main environmental challenge for the aluminum industry. Globally, the best result is obtained by maximizing aluminum production using green electrical energy from renewable sources. Aluminum production is categorized as an activity at very high risk of carbon leakage, which occurs when there is an increase in carbon dioxide emissions by new production in one country as a result of ceased production with emissions reduction in a second country with a strict climate policy.
Sharks, rays, and chimaeras (Class Chondrichthyes; herein ‘sharks’) are the earliest extant jawed vertebrates and exhibit some of the greatest functional diversity of all vertebrates. Ecologically, ...they influence energy transfer vertically through trophic levels and sometimes trophic cascades via direct consumption and predation risk. Through movements and migrations, they connect horizontally and temporally across habitats and ecosystems, integrating energy flows at large spatial scales and across time. This connectivity flows from ontogenetic growth in size and spatial movements, which in turn underpins their relatively low reproductive rates compared with other exploited ocean fishes. Sharks are also ecologically and demographically diverse and are taken in a wide variety of fisheries for multiple products (e.g. meat, fins, teeth, and gills). Consequently, a range of fisheries management measures are generally preferable to ‘silver bullet’ and ‘one size fits all’ conservation actions. Some species with extremely low annual reproductive output can easily become endangered and hence require strict protections to minimize mortality. Other, more prolific species can withstand fishing over the long term if catches are subject to effective catch limits throughout the species’ range. We identify, based on the IUCN Red List status, 64 endangered species in particular need of new or stricter protections and 514 species in need of improvements to fisheries management. We designate priority countries for such actions, recognizing the widely differing fishing pressures and conservation capacity. We hope that this analysis assists efforts to ensure this group of ecologically important and evolutionarily distinct animals can support both ocean ecosystems and human activities in the future.
Dulvy and colleagues delineate five key challenges to shark conservation, describe their approach for determining priority species and fisheries, and discuss the implications for conservation.
Heating consumes large amount of energy and is a primary source of greenhouse gas emission. Although energy-efficient buildings are developing quickly based on improving insulation and design, a ...large portion of energy continues to be wasted on heating empty space and nonhuman objects. Here, we demonstrate a system of personal thermal management using metallic nanowire-embedded cloth that can reduce this waste. The metallic nanowires form a conductive network that not only is highly thermal insulating because it reflects human body infrared radiation but also allows Joule heating to complement the passive insulation. The breathability and durability of the original cloth is not sacrificed because of the nanowires’ porous structure. This nanowire cloth can efficiently warm human bodies and save hundreds of watts per person as compared to traditional indoor heaters.
Molecular dating when rates vary Welch, John J.; Bromham, Lindell
Trends in ecology & evolution (Amsterdam),
06/2005, Letnik:
20, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Molecular-dating techniques potentially enable us to estimate the time of origin of any biological lineage. Such techniques were originally premised on the assumption of a ‘molecular clock’; that is, ...the assumption that genetic change accumulated steadily over time. However, it is becoming increasingly clear that constant rates of molecular evolution might be the exception rather than the rule. Recently, new methods have appeared that enable the incorporation of variable rates into molecular dating. Direct comparisons between these methods are difficult, because they differ in so many respects. However, the assumptions about rate change on which they rely fall into a few broad categories. Improving our understanding of molecular evolution will be an important next step towards evaluating and improving these methods.
Harnessing photoexcited "hot" carriers in metallic nanostructures could define a new phase of non-equilibrium optoelectronics for photodetection and photocatalysis. Surface plasmons are considered ...pivotal for enabling efficient operation of hot carrier devices. Clarifying the fundamental role of plasmon excitation is therefore critical for exploiting their full potential. Here, we measure the internal quantum efficiency in photoexcited gold (Au)-gallium nitride (GaN) Schottky diodes to elucidate and quantify the distinct roles of surface plasmon excitation, hot carrier transport, and carrier injection in device performance. We show that plasmon excitation does not influence the electronic processes occurring within the hot carrier device. Instead, the metal band structure and carrier transport processes dictate the observed hot carrier photocurrent distribution. The excellent agreement with parameter-free calculations indicates that photoexcited electrons generated in ultra-thin Au nanostructures impinge ballistically on the Au-GaN interface, suggesting the possibility for hot carrier collection without substantial energy losses via thermalization.
Structured populations, and replicated zones of contact between species, are an ideal opportunity to study regions of the genome with unusual levels of differentiation; and these can illuminate the ...genomic architecture of species isolation, and the spread of adaptive alleles across species ranges. Here, we investigated the effects of gene flow on divergence and adaptation in the Mytilus complex of species, including replicated parental populations in quite distant geographical locations. We used target enrichment sequencing of 1269 contigs of a few kb each, including some genes of known function, to infer gene genealogies at a small chromosomal scale. We show that geography is an important determinant of the genomewide patterns of introgression in Mytilus and that gene flow between different species, with contiguous ranges, explained up to half of the intraspecific outliers. This suggests that local introgression is both widespread and tends to affect larger chromosomal regions than purely intraspecific processes. We argue that this situation might be common, and this implies that genome scans should always consider the possibility of introgression from sister species, unsampled differentiated backgrounds, or even extinct relatives, for example Neanderthals in humans. The hypothesis that reticulate evolution over long periods of time contributes widely to adaptation, and to the spatial and genomic reorganization of genetic backgrounds, needs to be more widely considered to make better sense of genome scans.
Face-to-face cognitive testing is not always possible in large studies. Therefore, we assessed the telephone Montreal Cognitive Assessment (T-MoCA: MoCA items not requiring pencil and paper or visual ...stimulus) and the modified Telephone Interview of Cognitive Status (TICSm) against face-to-face cognitive tests in patients with transient ischemic attack (TIA) or stroke.
In a population-based study, consecutive community-dwelling patients underwent the MoCA and neuropsychological battery >1 year after TIA or stroke, followed by T-MoCA (22 points) and TICSm (39 points) at least 1 month later. Mild cognitive impairment (MCI) was diagnosed using modified Petersen criteria and the area under the receiver-operating characteristic curve (AUC) determined for T-MoCA and TICSm.
Ninety-one nondemented subjects completed neuropsychological testing (mean±SD age, 72.9±11.6 years; 54 males; stroke 49%) and 73 had telephone follow-up. MoCA subtest scores for repetition, abstraction, and verbal fluency were significantly worse (P<0.02) by telephone than during face-to-face testing. Reliability of diagnosis for MCI (AUC) were T-MoCA of 0.75 (95% confidence interval CI, 0.63-0.87) and TICSm of 0.79 (95% CI, 0.68-0.90) vs face-to-face MoCA of 0.85 (95% CI, 0.76-0.94). Optimal cutoffs were 18 to 19 for T-MoCA and 24 to 25 for TICSm. Reliability of diagnosis for MCI (AUC) was greater when only multi-domain impairment was considered (T-MoCA=0.85; 95% CI, 0.75-0.96 and TICSm=0.83, 95% CI, 0.70-0.96) vs face-to-face MoCA=0.87; 95% CI, 0.76-0.97).
Both T-MoCA and TICSm are feasible and valid telephone tests of cognition after TIA and stroke but perform better in detecting multi-domain vs single-domain impairment. However, T-MoCA is limited in its ability to assess visuoexecutive and complex language tasks compared with face-to-face MoCA.
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