Mercury is a highly toxic environmental pollutant with bioaccumulative properties. Therefore, new materials are required to not only detect but also effectively remove mercury from environmental sources, such as water. We herein describe a polyacrylamide hydrogel-based sensor functionalized with a thyminerich DNA that can simultaneously detect and remove mercury from water. Detection is achieved by selective binding of Hg 2+ between two thymine bases inducing a hairpin structure where upon addition of SYBR Green I dye green fluorescence is observed. In the absence of Hg 2+ , however, addition of the dye results in yellow fluorescence. Using the naked eye, the detection limit in a 50 mL water sample is 10 nM Hg 2+ . This sensor can be regenerated using a simple acid treatment and can remove Hg 2+ from water at a rate of ~1 hr -1 . This sensor was also used to detect and remove Hg 2+ from samples of Lake Ontario spiked with mercury. In addition, these hydrogel-based sensors are resistant to nuclease and can be rehydrated from dried gels for storage and DNA protection. Similar methods can be used to functionalize hydrogels with other nucleic acids, proteins, and small molecules for environmental and biomedical applications.

The presence of top predators can affect prey behaviour, morphology and life history, and thereby can produce indirect population consequences greater and further reaching than direct depredation would have alone. Raptor species in the Americas are recovering since restrictions on the use of dichlorodiphenyltrichloroethane (DDT) and the implementation of conservation measures, in effect constituting a hemisphere-wide predator-reintroduction experiment, and profound effects on populations of their prey are to be expected. Here, we document changes in the behaviour of western sandpipers (Calidris mauri ) at migratory stopover sites over two decades. Since 1985, migratory body mass and stopover durations of western sandpipers have fallen steadily at some stopovers in the Strait of Georgia, British Columbia. Comparisons between years, sites and seasons strongly implicate increasing danger from the recovery of peregrine falcons (Falco peregrinus) as a causal factor. A decade-long ongoing steep decline in sandpiper numbers censused on our study site is explained entirely by the shortening stopover duration, rather than fewer individuals using the site. Such behavioural changes are probably general among migratory shorebird species, and may be contributing to the widespread census declines reported in North America.

Background Repeat COVID-19 molecular testing can lead to positive test results after negative tests and to multiple positive test results over time. The association between positive tests and infectious virus is important to quantify. Methods A two months cohort of retrospective data and consecutively collected specimens from COVID-19 patients or patients under investigation were used to understand the correlation between prolonged viral RNA positive test results, cycle threshold (Ct) values and growth of SARS-CoV-2 in cell culture. Whole genome sequencing was used to confirm virus genotype in patients with prolonged viral RNA detection. Droplet digital PCR (ddPCR) was used to assess the rate of false negative COVID-19 diagnostic tests. Results In two months, 29,686 specimens were tested and 2,194 patients received repeated testing. Virus recovery in cell culture was noted in specimens with SARS-CoV-2 target genes’ Ct value average of 18.8 ± 3.4. Prolonged viral RNA shedding was associated with positive virus growth in culture in specimens collected up to 20 days after the first positive result but mostly in individuals symptomatic at time of sample collection. Whole genome sequencing provided evidence the same virus was carried over time. Positive tests following negative tests had Ct values higher than 29.5 and were not associated with virus culture. ddPCR was positive in 5.6% of negative specimens collected from COVID-19 confirmed or clinically suspected patients. Conclusions Low Ct values in SARS-CoV-2 diagnostic tests were associated with virus growth in cell culture. Symptomatic patients with prolonged viral RNA shedding can also be infectious.

Highly sensitive and selective DNA detection plays a central role in many fields of research and various assay platforms have been developed. Compared to homogeneous DNA detection, surface immobilized probes allow washing steps and signal amplification to give higher sensitivity. Previously research was focused on developing glass or gold based surfaces for DNA immobilization, we herein report hydrogel immobilized DNA. Specifically, acrydite-modified DNA was covalently functionalized to the polyacrylamide hydrogel during gel formation. There are several advantages of these DNAfunctionalized monolithic hydrogels. First, they can be easily handled in a way similar to that in homogeneous assays. Second, they have a low optical background where in combination with DNAfunctionalized gold nanoparticles, even ~0.1 nM target DNA can be visually detected. By using the attached gold nanoparticles to catalyze the reduction of Ag + , as low as 1 pM target DNA can be detected. The gels can be regenerated by a simple thermal treatment and the regenerated gels perform similarly compared to freshly prepared ones. The amount of gold nanoparticles adsorbed through DNA hybridization decreases with increasing gel percentage. Other parameters including DNA concentration, DNA sequence, ionic strength of the solution and temperature have also been systematically characterized in this study.

We report that a latitudinal cline in intertidal food distribution is associated with the nonbreeding distribution of the Western Sandpiper (Calidris mauri). This novel result is the first to demonstrate a clear relationship between patterns of differential nonbreeding distribution and food availability for any shorebird species. Within each age class and sex, longer-billed Western Sandpipers winter further south. Moreover, females, the longer-billed sex, tend to winter south of males. Thus, both inter- and intra-sexual clines in bill morphology result in an overall gradient of increasing bill length from north to south. Longer-billed birds are able to extract prey that are buried more deeply in the sediment; therefore, we predicted shifts in the vertical distribution of food resources to coincide with the clines in bill morphology across the nonbreeding range. We tested our prediction by measuring biofilm density and the vertical distribution of macrofaunal invertebrates at six nonbreeding sites. Although no latitudinal trend was observed for biofilm, the vertical distribution of invertebrates was consistent with our prediction and revealed that the greatest relative abundance of surface prey occurred at northern nonbreeding sites and declined with decreasing latitude. We discuss the potential implications of these findings in the context of competing evolutionary hypotheses of differential migration and bill dimorphism in shorebirds.

DNA-directed assembly of gold nanoparticles (AuNPs) has been extensively studied because of its important applications in analytical chemistry, materials science, and nanomedicine. In a typical system, two DNA-functionalized AuNPs are assembled via a linker DNA to form large aggregates. In majority of the previous reports, the linker DNA is fully base paired with no gaps or overhangs present. Introducing such non-base-paired regions in the linker DNA has been recently shown to be important for making stimuli-responsive materials and in crystallization of such AuNPs. In this work, we systematically studied the effect of introducing gaps and overhangs in the linker DNA to understand the kinetics of assembly and the melting transition of these aggregates. We found that the assembly kinetics decreased with increasing linker DNA length. The melting temperature decreased with the loss of base stacking by introducing gaps as well as the steric effect of overhangs. Additional insights were obtained by measuring the melting curves of the free DNAs in the absence of AuNPs. For example, it appeared that DNA base stacking at the nick site was favored in assembled nanoparticles compared to that in free DNA. Our results indicate that while it is possible to form AuNP assemblies with linker DNAs containing various types of unpaired regions, these kinetic and thermodynamic factors need to be considered when designing related sensors and materials.

Bimonthly beam-trawling from April 1991 to May 1992 and diver observations were used to assess distribution and large-scale movement of snow crabs, Chionoecetes opilio, over depths of 4-140 m in a bay of the northern Gulf of Saint Lawrence. Megalopae settled during October 1991. Immature crabs of instars I-IV (i.e., 3.3 -9.7 mm mean carapace width, CW) were found predominantly on bottoms -50-80 m deep and were cryptic and sedentary. Most immature crabs of instars V-VIII (i.e., 14.1 -34.5 mm mean CW) and adolescent males (i.e., producing sperm but not terminally moulted) migrated in winter to subtidal grounds, where they moulted. Movement to shallow waters was massive and resulted in a mean density of 860 crabs per 1000 m2 at -15 m in December 1991. Adult males (i.e., producing sperm and terminally moulted) of < 70 mm mean CW also moved to the shallow grounds from October to December 199 1, where some mated with pubescent -primiparous females (i .e., adult, first brood) from January to April 1992. Adult males of >90 mm mean CW were mainly found at depths > 80 m over most of the year, but from March to May 1992 an increase in mean CW of adult males at < 80 m indicated some upslope movement, probably to mate with multiparous females (i.e., adult, second or ulterior brood). Adult females were more gregarious and sedentary than adult males. We expand on the hypothesis that interannual variability in recruitment to adulthood tends to reflect differences in year-class strength, and that year-class strength varies in accordance with megalopal supply and (or) survivorship of cryptic instars.RCsumC : Un Cchantillonnage bimestriel rCalisC avec un chalut h perche, d'avril 1991 a mai 1992, et des observations en plongCe sous-marine ont Ct C effectuks afin de prCciser la distribution et les diplacements a grande Cchelle du Crabe des neiges, Chionoecetes opilio, entre 4 et 140 m de profondeur dans une baie du nord du golfe du Saint-Laurent. Les mCgalopes se sont Ctablies sur le fond en octobre 1991. Les crabes immatures des stades de mue I-IV (i.e., 3,3 -9,7 mm de largeur de carapace, LC, moyenne) ont Ct C retrouvks surtout entre -50-80 m de profondeur et Ctaient sCdentaires et cryptiques. La plupart des crabes immatures des stades de mue V -VIII (i.e., 14,l-34,5 mm LC moyenne) et les miles adolescents (i.e., produisant du sperme, mais pas en mue terminale) ont effectuk une migration hivernale vers l'infralittoral oh ils ont mu& Le mouvement vers les faibles profondeurs fut de grande ampleur et la densitC moyenne enregistrke h -15 m, en dCcembre 1991, Ctait de 860 crabes par 1000 m2. Les mQles adultes (i.e., produisant du sperme et en mue terminale) de LC moyenne <70 mm se sont aussi dCplacCs vers les fonds peu profonds d'octobre h dCcembre 1991, oh certains se sont accouplCs avec des femelles pubkres -primipares (i.e., adulte, premikre portCe) de janvier h avril 1992.Les miles adultes de LC moyenne >90 mm ont Ct C retrouvds surtout h des profondeurs > 80 m pour la majeure partie de l'annCe, mais de mars a mai 1992 un accroisse...

One of the constraints on fast-evolving viruses, such as influenza virus, is protein stability, or how strongly the folded protein holds together. Despite the importance of this protein property, there has been limited investigation of the impact of the stability of the influenza virus hemagglutinin protein—the primary antibody target of the immune system—on its evolution. Using a combination of computational estimates of stability and experiments, our analysis found that viruses with more-stable hemagglutinin proteins were associated with long-term persistence in the population. There are two potential reasons for the observed persistence. One is that more-stable proteins tolerate destabilizing mutations that less-stable proteins could not, thus increasing opportunities for immune escape. The second is that greater stability increases the fitness of the virus through increased production of infectious particles. Further research on the relative importance of these mechanisms could help inform the annual influenza vaccine composition decision process.