Neoproterozoic to early Phanerozoic rise in island arc redox state due to deep ocean oxygenation and increased marine sulfate levels

A rise in atmospheric O_2 levels between 800 and 400 Ma is thought to have oxygenated the deep oceans, ushered in modern biogeochemical cycles, and led to the diversification of animals. Over the same time interval, marine sulfate concentrations are also thought to have increased to near-modern levels. We present compiled data that indicate Phanerozoic island arc igneous rocks are more oxidized (Fe^(3+)/ΣFe ratios are elevated by 0.12) vs. Precambrian equivalents. We propose this elevation is due to increases in deep-ocean O_2 and marine sulfate concentrations between 800 and 400 Ma, which oxidized oceanic crust on the seafloor. Once subducted, this material oxidized the subarc mantle, increasing the redox state of island arc parental melts, and thus igneous island arc rocks. We test this using independently compiled V/Sc ratios, which are also an igneous oxybarometer. Average V/Sc ratios of Phanerozoic island arc rocks are elevated (by +1.1) compared with Precambrian equivalents, consistent with our proposal for an increase in the redox state of the subarc mantle between 800 and 400 Ma based on Fe^(3+)/ΣFe ratios. This work provides evidence that the more oxidized nature of island arc vs. midocean-ridge basalts is related to the subduction of material oxidized at the Earth’s surface to the subarc mantle. It also indicates that the rise of atmospheric O_2 and marine sulfate to near-modern levels by the late Paleozoic influenced not only surface biogeochemical cycles and animal diversification but also influenced the redox state of island arc rocks, which are building blocks of continental crust

Beating resonance patterns and orthogonal wave propagation due to zero-group-velocity guided elastic waves

Elastic waves in anisotropic media can exhibit a power flux that is not collinear with the wave vector. We show that this has remarkable consequences for the zero-group-velocity (ZGV) resonances that appear in an infinite plate. True ZGV resonances, in the sense that the guided wave's overall power flux vanishes while its wavelength remains finite, are only found when the wave vector is oriented along a principal axis of the material. At other propagation angles, "quasi-ZGV" waves are found for which the power flux is orthogonal to the wave vector. We present original measurements of such a wave field in a single crystal silicon wafer. As a consequence of the nonzero power flux of qZGV waves, time acts as a filter in the wave vector domain that selects precisely the eight plane waves corresponding to true ZGV resonances. This intuitively explains the highly symmetric resonance pattern that emerges naturally on the surface of the plate after a pulsed point source excitation. We showcase a direct measurement of this beating pattern. The developed physical understanding paves the way towards novel designs of surface acoustic wave devices and is of high relevance for ultrasonic nondestructive evaluation.Comment: 10 pages, 9 figure

Mercury Reduces Avian Reproductive Success and Imposes Selection: An Experimental Study with Adult- or Lifetime-Exposure in Zebra Finch

Mercury is a global pollutant that biomagnifies in food webs, placing wildlife at risk of reduced reproductive fitness and survival. Songbirds are the most diverse branch of the avian evolutionary tree; many are suffering persistent and serious population declines and we know that songbirds are frequently exposed to mercury pollution. Our objective was to determine the effects of environmentally relevant doses of mercury on reproductive success of songbirds exposed throughout their lives or only as adults. The two modes of exposure simulated philopatric species versus dispersive species, and are particularly relevant because of the heightened mercury-sensitivity of developing nervous systems. We performed a dosing study with dietary methylmercury in a model songbird species, the zebra finch (Taeniopygia guttata), at doses from 0.3 – 2.4 parts per million. Birds were exposed to mercury either as adults only or throughout their lives. All doses of mercury reduced reproductive success, with the lowest dose reducing the number of independent offspring produced in one year by 16% and the highest dose, representing approximately half the lethal dose for this species, causing a 50% reduction. While mercury did not affect clutch size or survivorship, it had the most consistent effect on the proportion of chicks that fledged from the nest, regardless of mode of exposure. Among birds exposed as adults, mercury caused a steep increase in the latency to re-nest after loss of a clutch. Birds exposed for their entire lifetimes, which were necessarily the offspring of dosed parents, had up to 50% lower reproductive success than adult-exposed birds at low doses of methylmercury, but increased reproductive success at high doses, suggesting selection for mercury tolerance at the highest level of exposure. Our results indicate that mercury levels in prey items at contaminated sites pose a significant threat to populations of songbirds through reduced reproductive success

Mother\u27s own milk compared with formula milk for feeding preterm or low birth weight infants: Systematic review and meta-analysis

Objectives: We assessed the effect of feeding preterm or low birth weight infants with infant formula compared with mother\u27s own milk on mortality, morbidity, growth, neurodevelopment, and disability. Methods: We searched Medline (Ovid), Embase (Ovid), and Cochrane Central Register of Controlled Studies to October 1, 2021. Results: Forty-two studies enrolling 89 638 infants fulfilled the inclusion criteria. We did not find evidence of an effect on mortality (odds ratio [OR] 1.26, 95% confidence interval [CI] 0.91-1.76), infection (OR 1.52, 95% CI 0.98-2.37), cognitive neurodevelopment (standardized mean difference -1.30, 95% CI -3.53 to 0.93), or on growth parameters. Formula milk feeding increased the risk of necrotizing enterocolitis (OR 2.99, 95% CI 1.75-5.11). The Grading of Recommendations Assessment, Development, and Evaluation certainty of evidence was low for mortality and necrotizing enterocolitis, and very low for neurodevelopment and growth outcomes. Conclusions: In preterm and low birth weight infants, low to very low-certainty evidence indicates that feeding with infant formula compared with mother\u27s own milk has little effect on all-cause mortality, infection, growth, or neurodevelopment, and a higher risk of developing necrotizing enterocolitis

Blood Mercury Levels of Zebra Finches Are Heritable: Implications for the Evolution of Mercury Resistance

Mercury is a ubiquitous metal contaminant that negatively impacts reproduction of wildlife and has many other sub-lethal effects. Songbirds are sensitive bioindicators of mercury toxicity and may suffer population declines as a result of mercury pollution. Current predictions of mercury accumulation and biomagnification often overlook possible genetic variation in mercury uptake and elimination within species and the potential for evolution in affected populations. We conducted a study of dietary mercury exposure in a model songbird species, maintaining a breeding population of zebra finches (Taeniopygia guttata) on standardized diets ranging from 0.0–2.4 μg/g methylmercury. We applied a quantitative genetics approach to examine patterns of variation and heritability of mercury accumulation within dietary treatments using a method of mixed effects modeling known as the \u27animal model\u27. Significant variation in blood mercury accumulation existed within each treatment for birds exposed at the same dietary level; moreover, this variation was highly repeatable for individuals. We observed substantial genetic variation in blood mercury accumulation for birds exposed at intermediate dietary concentrations. Taken together, this is evidence that genetic variation for factors affecting blood mercury accumulation could be acted on by selection. If similar heritability for mercury accumulation exists in wild populations, selection could result in genetic differentiation for populations in contaminated locations, with possible consequences for mercury biomagnification in food webs

Practical Spectrophotometric Assay for the \u3cem\u3edapE\u3c/em\u3e-Encoded \u3cem\u3eN\u3c/em\u3e-Succinyl-L,L-Diaminopimelic Acid Desuccinylase, a Potential Antibiotic Target

A new enzymatic assay for the bacterial enzyme succinyl-diaminopimelate desuccinylase (DapE, E.C. 3.5.1.18) is described. This assay employs N6-methyl-N2-succinyl-L,L-diaminopimelic acid (N6-methyl-L,L-SDAP) as the substrate with ninhydrin used to detect cleavage of the amide bond of the modified substrate, wherein N6-methylation enables selective detection of the primary amine enzymatic product. Molecular modeling supported preparation of the mono-N6-methylated-L,L-SDAP as an alternate substrate for the assay, given binding in the active site of DapE predicted to be comparable to the endogenous substrate. The alternate substrate for the assay, N6-methyl-L,L-SDAP, was synthesized from the tert-butyl ester of Boc-L-glutamic acid employing a Horner-Wadsworth-Emmons olefination followed by an enantioselective reduction employing Rh(I)(COD)(S,S)-Et-DuPHOS as the chiral catalyst. Validation of the new ninhydrin assay was demonstrated with known inhibitors of DapE from Haemophilus influenza (HiDapE) including captopril (IC50 = 3.4 [± 0.2] μM, 3-mercaptobenzoic acid (IC50 = 21.8 [±2.2] μM, phenylboronic acid (IC50 = 316 [± 23.6] μM, and 2-thiopheneboronic acid (IC50 = 111 [± 16] μM. Based on these data, this assay is simple and robust, and should be amenable to high-throughput screening, which is an important step forward as it opens the door to medicinal chemistry efforts toward the discovery of DapE inhibitors that can function as a new class of antibiotics

Spatial distribution of shore-based fishers in the greater Perth Metropolitan area over summer 2010/2011

Aerial surveys are a useful technique for estimating numbers of recreational fishers. Following the success of a pilot study to examine the spatial patterns of recreational shore-based fishing activity in the Perth Metropolitan area from April – June 2010, another survey was conducted from December 2010 – February 2011 between Lancelin – Bunbury. More than 7,000 shorebased fishers were counted during 36 aerial flights, with significantly more recorded on morning and afternoon flights, when compared to those conducted at midday. Flights on weekends/public holidays also recorded more fishers than weekdays. The spatial distribution of fishers was variable along the coast, with sandy beaches at the northern and southern sections of the study area having high counts of fishers, along with groynes in the central section. Comparisons with the previous (autumn) study revealed that the northern beaches generally had higher numbers of shore-based fishers in summer, while those in the south had more during autumn. Data from this study assists with understanding the patterns of shore-based recreational fishing occurring along the greater Perth Metropolitan coast. Such information can be used to assist in the design of future on-ground surveys, compliance and education activities

The response of crib-biting and windsucking in horses to dietary supplementation with an antacid mixture

A douoble blind placebo controlled study to evaluate the effect of two levels of antacid supplementation on crib-biting behaviour in horse

The Role of a General Safety Requirement in Canada's Health Protection Regime

This research was supported in part by a financial contribution from the Health Policy Research Program, Health Canada