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The global growth of an aging population is expected to coincide with an increase in aging-related pathologies, including those related to brain health. Thus, the potential for accelerated cognitive health declines due to adverse aging is expected to have profound social and economic implications. However, the progression to pathological conditions is not an inevitable part of aging. In fact, engaging in activities that improve cardiovascular fitness appears to be a means that offers the benefits of maintaining and/or improving cognitive health in older age. However, to date, the underlying mechanisms responsible for improved central nervous system health and function with exercise are not yet fully elucidated. Consequently, there is considerable interest in studies aimed at understanding the neurophysiological benefits of exercise on aging. One such area of study suggests that the improvements in brain health via exercise are, in part, driven by the recovery of inhibitory processes related to the neurotransmitter gamma-aminobutyric acid (GABA). In the present review, we highlight the opposing effects of aging and exercise on cortical inhibition and the GABAergic system’s functional integrity. We highlight these changes in GABA function by reviewing work with in vivo measurements: transcranial magnetic stimulation (TMS) and magnetic resonance spectroscopy (MRS). We also highlight recent and significant technological and methodological advances in assessing the GABAergic system’s integrity with TMS and MRS. We then discuss potential future research directions to inform mechanistic GABA study targeted to improve health and function in aging. We conclude by highlighting the significance of understanding the effects of exercise and aging, its influence on GABA levels, and why a better understanding is crucial to allow for more targeted and effective interventions aimed to ultimately improve age-related decline in aging.

Abstract Primate faces provide information about a range of variant and invariant traits, including some that are relevant for mate choice. For example, faces of males may convey information about their health or genetic quality through symmetry or facial masculinity. Because perceiving and processing such information may have bearing on the reproductive success of an individual, cognitive systems are expected to be sensitive to facial cues of mate quality. However, few studies have investigated this topic in non-human primate species. Orang-utans are an interesting species to test mate-relevant cognitive biases, because they are characterised by male bimaturism: some adult males are fully developed and bear conspicuous flanges on the side of their face, while other males look relatively similar to females. Here, we describe two non-invasive computerised experiments with Bornean orang-utans (Pongo pygmaeus), testing (i) immediate attention towards large flanges and symmetrical faces using a dot-probe task (N = 3 individuals; 2F) and (ii) choice bias for pictures of flanged males over unflanged males using a preference test (N = 6 individuals; 4F). In contrast with our expectations, we found no immediate attentional bias towards either large flanges or symmetrical faces. In addition, individuals did not show a choice bias for stimuli of flanged males. We did find exploratory evidence for a colour bias and energy efficiency trade-offs in the preference task. We discuss our null results and exploratory results in the context of the evolutionary history of Bornean orang-utans, and provide suggestions for a more biocentric approach to the study of orang-utan cognition.

Abstract Background Clostridium spp. has demonstrated therapeutic potential in cancer treatment through intravenous or intratumoral administration. This approach has expanded to include non-pathogenic clostridia for the treatment of various diseases, underscoring the innovative concept of oral-spore vaccination using clostridia. Recent advancements in the field of synthetic biology have significantly enhanced the development of Clostridium-based bio-therapeutics. These advancements are particularly notable in the areas of efficient protein overexpression and secretion, which are crucial for the feasibility of oral vaccination strategies. Here, we present two examples of genetically engineered Clostridium candidates: one as an oral cancer vaccine and the other as an antiviral oral vaccine against SARS-CoV-2. Results Using five validated promoters and a signal peptide derived from Clostridium sporogenes, a series of full-length NY-ESO-1/CTAG1, a promising cancer vaccine candidate, expression vectors were constructed and transformed into C. sporogenes and Clostridium butyricum. Western blotting analysis confirmed efficient expression and secretion of NY-ESO-1 in clostridia, with specific promoters leading to enhanced detection signals. Additionally, the fusion of a reported bacterial adjuvant to NY-ESO-1 for improved immune recognition led to the cloning difficulties in E. coli. The use of an AUU start codon successfully mitigated potential toxicity issues in E. coli, enabling the secretion of recombinant proteins in C. sporogenes and C. butyricum. We further demonstrate the successful replacement of PyrE loci with high-expression cassettes carrying NY-ESO-1 and adjuvant-fused NY-ESO-1, achieving plasmid-free clostridia capable of secreting the antigens. Lastly, the study successfully extends its multiplex genetic manipulations to engineer clostridia for the secretion of SARS-CoV-2-related Spike_S1 antigens. Conclusions This study successfully demonstrated that C. butyricum and C. sporogenes can produce the two recombinant antigen proteins (NY-ESO-1 and SARS-CoV-2-related Spike_S1 antigens) through genetic manipulations, utilizing the AUU start codon. This approach overcomes challenges in cloning difficult proteins in E. coli. These findings underscore the feasibility of harnessing commensal clostridia for antigen protein secretion, emphasizing the applicability of non-canonical translation initiation across diverse species with broad implications for medical or industrial biotechnology.

Intra-crystalline protein degradation (IcPD) analysis was undertaken on 80 fossil tooth enamel samples from four taxonomic groups (rhinocerotid, suid, equid, bovid) excavated from two archaeological cave sites in Zambia (Twin Rivers and Mumbwa Caves). Seventy-two (90%) of these fossils showed evidence of closed-system behaviour. The fossils’ relative extent of protein degradation between the sites was consistent with their known ages, with samples from Twin Rivers (Mid-Pleistocene) showing higher levels of degradation than Mumbwa Caves (late Mid-Pleistocene to late Holocene). At Twin Rivers, a potential trend between IcPD and excavation depth was observed, concordant with the working hypothesis of periodic deposition of sediments as slurry flows into a phreatic passage. However, greater depositional and taphonomic complexity was indicated by relatively wide ranges of IcPD values within individual excavation levels. These results are interpreted partly as the consequence of the excavation methods used, alongside reworking within the deposits, which had not previously been recognised. Whilst lack of stratigraphic control limited the investigation of taxonomic effect, one notable difference in the protein breakdown pattern of peptide chain hydrolysis was observed between rhinocerotid in comparison to the other studied taxa. We therefore recommend taxon-specific enamel amino acid geochronologies (AAGs) are developed in future. Whilst lack of comparator datasets meant it was not possible to create a calibrated, enamel AAG for the South-Central African region from these sites, Twin Rivers provides a case study illustrating the complexity of cave formation processes and the importance of direct dating for interpreting archaeological and palaeontological sequences.

Supplemental food from anthropogenic sources is a source of conflict with humans for many wildlife species. Food-seeking behaviours by black bears Ursus americanus and brown bears Ursus arctos can lead to property damage, human injury and mortality of the offending bears. Such conflicts are a well-known conservation management issue wherever people live in bear habitats. In contrast, the use of anthropogenic foods by the polar bear Ursus maritimus is less common historically but is a growing conservation and management issue across the Arctic. Here we present six case studies that illustrate how negative food-related interactions between humans and polar bears can become either chronic or ephemeral and unpredictable. Our examination suggests that attractants are an increasing problem, exacerbated by climate change-driven sea-ice losses that cause increased use of terrestrial habitats by bears. Growing human populations and increased human visitation increase the likelihood of human–polar bear conflict. Efforts to reduce food conditioning in polar bears include attractant management, proactive planning and adequate resources for northern communities to reduce conflicts and improve human safety. Permanent removal of unsecured sources of nutrition, to reduce food conditioning, should begin immediately at the local level as this will help to reduce polar bear mortality.

Introduction Inflammatory bowel diseases (IBD) are immune-mediated conditions that are increasing in incidence and prevalence worldwide. Their assessment and monitoring are becoming increasingly important, though complex. The best disease control is achieved through tight monitoring of objective inflammatory parameters (such as serum and stool inflammatory markers), cross-sectional imaging and endoscopic assessment. Considering the complexity of the information obtained throughout a patient’s journey, artificial intelligence (AI) provides an ideal adjunct to existing tools to help diagnose, monitor and predict the course of disease of patients with IBD. Therefore, we propose a scoping review assessing AI’s role in diagnosis, monitoring and prognostication tools in patients with IBD. We aim to detect gaps in the literature and address them in future research endeavours.Methods and analysis We will search electronic databases, including Medline, Embase, Cochrane CENTRAL, CINAHL Complete, Web of Science and IEEE Xplore. Two reviewers will independently screen the abstracts and titles first and then perform the full-text review. A third reviewer will resolve any conflict. We will include both observational studies and clinical trials. Study characteristics will be extracted using a data extraction form. The extracted data will be summarised in a tabular format, following the imaging modality theme and the study outcome assessed. The results will have an accompanying narrative review.Ethics and dissemination Considering the nature of the project, ethical review by an institutional review board is not required. The data will be presented at academic conferences, and the final product will be published in a peer-reviewed journal.

ABSTRACT Clostridium species have gained attention in industrial and medical applications, and the development of genetic tools has enabled the advancement of the CRISPR-Cas systems for these bacteria. Compared to the primarily used Cas9 from Streptococcus pyogenes, the utilization of Cas12a (previously known as Cpf1) proteins remains incomplete in clostridia, although they exhibit potential advantages, including T-rich recognition for Clostridium genomes and lower toxicity. In this study, we expanded the CRISPR-Cas tools in clostridia by establishing a CRISPR-Cas12a system with two different cas12a genes (Ascas12a from Acidaminococcus and Fncas12a from Francisella novicida). The optimized tetracycline-inducible systems were initially determined by the glucuronidase reporter and were used to drive expression of the cas12a genes and crRNAs. Our results demonstrate that the CRISPR-FnCas12a system offers flexible target selection in clostridia, and a specific folding pattern of the precursor crRNA is important to enable high mutation generation efficiency. By using sacB (encoding levansucrase) as a negative marker for plasmid curing and determining the optimal size of the donor DNA template for gene integration in the CRISPR-FnCas12a system, we achieved highly efficient and rapid genome modification, exemplified by the successful engineering of clostridia (Clostridium butyricum and Clostridium sporogenes) to produce near-infrared fluorescence from biliverdin and hemin. IMPORTANCE Continued efforts in developing the CRISPR-Cas systems will further enhance our understanding and utilization of Clostridium species. This study demonstrates the development and application of a genome-engineering tool in two Clostridium strains, Clostridium butyricum and Clostridium sporogenes, which have promising potential as probiotics and oncolytic agents. Particular attention was given to the folding of precursor crRNA and the role of this process in off-target DNA cleavage by Cas12a. The results provide the guidelines necessary for efficient genome engineering using this system in clostridia. Our findings not only expand our fundamental understanding of genome-engineering tools in clostridia but also improve this technology to allow use of its full potential in a plethora of biotechnological applications.

Despite considerable clinical success, the potential of cancer immunotherapy is restricted by a lack of tumour-targeting strategies. Treatment requires systemic delivery of cytokines or antibodies at high levels to achieve clinically effective doses at malignant sites. This is exacerbated by poor penetration of tumour tissue by therapeutic antibodies. High-grade immune-related adverse events (irAEs) occur in a significant number of patients (5-15%, cancer- and therapeutic-dependent) that can lead to lifelong issues and can exclude from treatment patients with pre-existing autoimmune diseases. Tumour-homing bacteria, genetically engineered to produce therapeutics, is one of the approaches that seeks to mitigate these drawbacks. The ability of Clostridium sporogenes to form spores that are unable to germinate in the presence of oxygen (typical of healthy tissue) offers a unique advantage over other vectors. However, the limited utility of existing gene editing tools hinders the development of therapeutic strains. To overcome the limitations of previous systems, expression of the Cas9 protein and the gRNA was controlled using tetracycline inducible promoters. Furthermore, the components of the system were divided across two plasmids, improving the efficiency of cloning and conjugation. Genome integrated therapeutic genes were assayed biochemically and in cell-based functional assays. The potency of these strains was further improved through rationally-conceived gene knock-outs. The new system was validated by demonstrating the efficient addition and deletion of large sequences from the genome. This included the creation of recombinant strains expressing two pro-inflammatory cytokines, interleukin-2 (IL-2) and granulocyte macrophage-colony stimulating factor (GM-CSF), and a pro-drug converting enzyme (PCE). A comparative, temporal in vitro analysis of the integrant strains and their plasmid-based equivalents revealed a substantial reduction of cytokine activity in chromosome-based constructs. To compensate for this loss, a 7.6 kb operon of proteolytic genes was deleted from the genome. The resultant knock-out strains showed an 8- to 10-fold increase in cytokine activity compared to parental strains.

Arthropods play a crucial role in terrestrial ecosystems, for instance in mediating energy fluxes and in forming the food base for many organisms. To better understand their functional role in such ecosystem processes, monitoring of trends in arthropod biomass is essential. Obtaining direct measurements of the body mass of individual specimens is laborious. Therefore, these data are often indirectly acquired by utilizing allometric length-biomass relationships based on a correlative parameter, such as body length. Previous studies have often used such relationships with a low taxonomic resolution and/or small sample size and/or adopted regressions calibrated in different biomes. Despite the scientific interest in the ecology of arctic arthropods, no site-specific family-level length-biomass relationships have hitherto been published. Here we present 27 family-specific length-biomass relationships from two sites in the High Arctic: Zackenberg in northeast Greenland and Knipovich in north Taimyr, Russia. We show that length-biomass regressions from different sites within the same biome did not affect estimates of phenology but did result in substantially different estimates of arthropod biomass. Estimates of daily biomass at Zackenberg were on average 24% higher when calculated using regressions for Knipovich compared to using regressions for Zackenberg. In addition, calculations of daily arthropod biomass at Zackenberg based on order-level regressions from frequently cited studies in literature revealed overestimations of arthropod biomass ranging from 69.7% to 130% compared to estimates based on regressions for Zackenberg. Our results illustrate that the use of allometric relationships from different sites can significantly alter the biological interpretation of, for instance, the interaction between insectivorous birds and their arthropod prey. We conclude that length-biomass relationships should be locally established rather than being based on global relationships.

Abstract Physical attractiveness plays a crucial role in mate choice for both men and women. This is reflected in visual attention: people immediately attend towards and look longer at attractive faces, especially when they are motivated to find a partner. However, previous studies did not incorporate real-life dating decisions. Here, we aimed to combine attentional tasks with individual attractiveness ratings and a real-life mate choice context, namely a speed-dating paradigm. We investigated whether heterosexual non-committed young adults showed biases in immediate and voluntary attention towards attractive faces and preferred dating partners. In line with previous research, we found considerable individual differences in individual attractiveness preferences. Furthermore, our results showed that men had a bias towards attractive faces and preferred dating partners in the immediate attention task, while results for women were mixed. In the voluntary attention task, however, both men and women had an attentional bias towards attractive faces and preferred dating partners. Our results suggest that individual attractiveness preferences are good predictors of especially voluntary attention. We discuss these findings from an evolutionary perspective and suggest directions for future research.

Summary: Reported herein is a new set of vectors designed to streamline molecular cloning and genome editing by exploiting modern cloning methods. The new vectors build on the existing pMTL8000 vectors that have been a staple of Clostridium research for more than a decade. The introduction of two pairs of type IIS restriction sites flanking an insulated multiple cloning site in both a cloning vector and a CRISPR-Cas9 gene editing vector enables plasmid construction in a “one-pot” reaction, avoiding the more laborious steps of conventional cloning. A synthetic lacZα expression cassette introduced between the cloning sites enables visual detection of background colonies. In addition, distinct selection markers on each vector permit selection of the desired clones according to antibiotic resistance. An example of strain development using the new vectors is demonstrated.

Abstract An important vision of modern magnetic research is to use antiferromagnets (AFMs) as controllable and active ultrafast components in spintronic devices. Hematite (α‐Fe2O3) is a promising model material in this respect because its pronounced Dzyaloshinskii‐Moriya interaction leads to the coexistence of antiferromagnetism and weak ferromagnetism. Here, femtosecond laser pulses are used to drive terahertz (THz) spin currents from α‐Fe2O3 into an adjacent Pt layer. Two contributions to the generation of the spin current with distinctly different dynamics are found: the impulsive stimulated Raman scatting that relies on the AFM order and the ultrafast spin Seebeck effect that relies on the net magnetization. The total THz spin current dynamics can be manipulated by a medium‐strength magnetic field below 1 T. The control of the THz spin current achieved in α‐Fe2O3 opens the pathway toward tailoring the exact spin current dynamics from ultrafast AFM spin sources.

Abstract Sloth bears behave aggressively toward humans when threatened and are among the most dangerous wildlife in India. Safety messaging for those who live in sloth bear country must be accurate to be effective, and messaging may need to be modified to account for regional differences in human-bear relationships. The timing of sloth bear attacks on the Deccan Plateau of Karnataka, both by season and by time of day, deviated enough from those reported in other areas such that it warranted further investigation. We compared data from eight studies of human-sloth bear conflict from across the Indian subcontinent and explored possibilities as to why differences exist. Seasonally all studies reported that human-sloth bear conflict was highest when human activity in the forest was greatest, though the season of highest human activity varied significantly by region (χ 2 = 5921, df = 5, P

Abstract Transition‐metal dichalcogenides (TMDCs) are an aspiring class of materials with unique electronic and optical properties and potential applications in spin‐based electronics. Here, terahertz emission spectroscopy is used to study spin‐to‐charge current conversion (S2C) in the TMDC NbSe2 in ultra‐high‐vacuum‐grown F|NbSe2 thin‐film stacks, where F is a layer of ferromagnetic Fe or Ni. Ultrafast laser excitation triggers an ultrafast spin current that is converted into an in‐plane charge current and, thus, a measurable THz electromagnetic pulse. The THz signal amplitude as a function of the NbSe2 thickness shows that the measured signals are fully consistent with an ultrafast optically driven injection of an in‐plane‐polarized spin current into NbSe2. Modeling of the spin‐current dynamics reveals that a sizable fraction of the total S2C originates from the bulk of NbSe2 with the opposite, negative sign of the spin Hall angle as compared to Pt. By a quantitative comparison of the emitted THz radiation from F|NbSe2 to F|Pt reference samples and the results of ab initio calculations, it is estimated that the spin Hall angle of NbSe2 for an in‐plane polarized spin current lies between ‐0.2% and ‐1.1%, while the THz spin‐current relaxation length is of the order of a few nanometers.

Abstract Understanding what drives changes in wildlife demography is fundamental to the conservation and management of depleted or declining populations, though making inference about the intrinsic and extrinsic factors that influence survival and reproduction remains challenging. Here we use mark–resight data from 2000 to 2018 to examine the effects of environmental variability on age‐specific survival and natality for the endangered western distinct population segment (wDPS) of Steller sea lions (Eumetopias jubatus) in Alaska, USA. Though this population has been studied extensively over the last four decades, the causes of divergent abundance trends that have been observed across the wDPS range remain unknown. We developed a Bayesian multievent mark–resight model that accounts for female reproductive state uncertainty. Annual survival probabilities for male pups (0.44; 0.36–0.53), female yearlings (0.63; 0.49–0.73), and male yearlings (0.62; 0.51–0.71) born in the western portion of the wDPS range, estimated here for the first time, were lower than those in the eastern portion of the wDPS range, estimated as: male pups (0.69; 0.65–0.74), female yearlings (0.76; 0.71–0.81), and male yearlings (0.71; 0.65–0.78). There was a higher proportion of young female breeders in the western portion of the range, but overall natality was lower (0.69; 0.47–0.96) than in the eastern portion of the range (0.80; 0.74–0.84). Additionally, pup mass had a positive effect on pup survival in the eastern portion of the range and a negative effect in the western portion of the range, potentially due to earlier weaning of heavier pups. Local‐ and basin‐scale oceanographic features such as the Aleutian Low, the Arctic Oscillation Index, the North Pacific Gyre Oscillation, chlorophyll concentration, upwelling, and wind in certain seasons were correlated with vital rates. However, drawing strong inferences from these correlations is challenging given that relationships between ocean conditions and an adaptive top predator in a dynamic ecosystem are exceedingly complex. This study provides the first demographic rate estimates for the western portion of the range where abundance estimates continue to decline. These results will advance efforts to identify factors driving regionally divergent abundance trends, with implications for population‐level responses to future climate variability.

Abstract Background Pressure pain thresholds (PPTs) are commonly assessed to quantify mechanical sensitivity in various conditions, including migraine. Digital and analogue algometers are used, but the concurrent validity between these algometers is unknown. Therefore, we assessed the concurrent validity between a digital and analogue algometer to determine PPTs in healthy participants and people with migraine. Methods Twenty-six healthy participants and twenty-nine people with migraine participated in the study. PPTs were measured interictally and bilaterally at the cephalic region (temporal muscle, C1 paraspinal muscles, and trapezius muscle) and extra-cephalic region (extensor carpi radialis muscle and tibialis anterior muscle). PPTs were first determined with a digital algometer, followed by an analogue algometer. Intraclass correlation coefficients (ICC3.1) and limits of agreement were calculated to quantify concurrent validity. Results The concurrent validity between algometers in both groups was moderate to excellent (ICC3.1 ranged from 0.82 to 0.99, with 95%CI: 0.65 to 0.99). Although PPTs measured with the analogue algometer were higher at most locations in both groups (p

Salmonella occurs in all the major meat producing livestock species (ruminants, swine and poultry), most often residing within the gastrointestinal tract asymptomatically. While considerable success has been achieved post-harvest, the design of effective pre-harvest interventions to control Salmonella has lagged. A simplistic view of the extremely complex host/pathogen interaction suggests that the pathogen has a vested interest in not causing illness or death to the host. The former would initiate an immune response from the host and/or the application of therapeutic antibacterial agents, while the latter would require finding another suitable host. Due to the widespread prevalence of Salmonella within livestock and poultry, and the relatively few salmonellosis cases in comparison, it appears, and is supported by new research, that Salmonella has developed methods to avoid detection by the animal’s immune system and live essentially as a commensal organism within the gastrointestinal tract of the animal. Yet, for reasons that are not fully understood, this “commensal” Salmonella does on occasion become virulent, in young and mature animals alike. Indeed, these researchers have documented Salmonella carriage throughout the year in cattle, but only rarely, if at all, was salmonellosis observed. Further, evaluation of Salmonella isolates (serotype and antimicrobial resistance patterns) from sick and healthy cattle failed to explain that while Salmonella was present in the majority of cattle sampled on that farm, only a few developed salmonellosis. Virulence, as well as multi-drug resistance, in both livestock and humans appears to cluster within a few serotypes. As a result, petitions are circulating calling for the labeling of some Salmonella serotypes as adulterants, as was done with Escherichia coli O157:H7 and other enterohemorrhagic E. coli strains. Regulators are considering approaching the Salmonella problem by serotype, such as focusing specifically on the top 10 reported serotypes causing human illness. Herein, the authors will discuss the many challenges of controlling Salmonella pre-harvest, reflecting on the significant research portfolio that has been generated over the last 25 years, as well as challenging existing paradigms surrounding this pathogen and the experimental methods used to further our understanding of Salmonella and/or evaluate methods of control.

Abstract Many organisms reproduce in seasonal environments, where selection on timing of reproduction is particularly strong as consumers need to synchronize reproduction with the peaked occurrence of their food. When a consumer species changes its phenology at a slower rate than its resources, this may induce a trophic mismatch, that is, offspring growing up after the peak in food availability, potentially leading to reductions in growth and survival. However, there is large variation in the degree of trophic mismatches as well as in its effects on reproductive output. Here, we explore the potential causes for variation in the strength of trophic mismatches in published studies of birds. Specifically, we ask whether the changes in the degree of mismatch that have occurred over time can be explained by a bird's (a) breeding latitude, (b) migration distance, and/or (c) life‐history traits. We found that none of these three factors explain changes in the degree of mismatch over time. Nevertheless, food phenology did advance faster at more northerly latitudes, while shifts in bird phenology did not show a trend with latitude. We argue that the lack of support in our results is attributable to the large variation in the metrics used to describe timing of food availability. We propose a pathway to improve the quantification of trophic mismatches, guided by a more rigorous understanding of links between consumers and their resources.

Abstract The Arabian Peninsula is a critical geographic landmass situated between Africa and the rest of Eurasia. Climatic shifts across the Pleistocene periodically produced wetter conditions in Arabia, dramatically altering the spatial distribution of hominins both within and between continents. This is particularly true of Acheulean hominins, who appear to have been more tethered to water sources than Middle Palaeolithic hominins. However, until recently, chrono-cultural knowledge of the Acheulean of Arabia has been limited to one dated site, which indicated a hominin presence in Marine Isotope Stages (MIS) 7–6. Here, we report the first dated Acheulean site from the Nefud Desert of northern Saudi Arabia, together with palaeoecological evidence for an associated deep, probably fresh-water, lake. The site of An Nasim features varied and often finely flaked façonnage handaxes. Luminescence ages together with geomorphological and palaeoecological evidence indicates that the associated artefacts date to MIS 9. At present, An Nasim represents the oldest yet documented Acheulean sites in Arabia, and adds to a growing picture of regionally diverse stone tool assemblages used by Middle Pleistocene hominins, and likely indicative of repeated population re-entry into the peninsula in wet ‘Green Arabia’ phases.

Seasonal variation in the composition of avian communities is poorly documented in African montane forests. Using field observations, mist-netting data (63,424 NMH), recording of mixed-species flocks (160 flocks noted), and of the feeding ecology of greenbuls (757 observations), we document marked seasonal changes in a bird community in an East African montane forest (1,340–2,130 m) in the Udzungwa Mountains in south-central Tanzania. This mountain range contains the largest remaining forests in the Eastern Arc Mountains in Tanzania, part of a key global biodiversity hotspot. Our analysis is based on data in the dry and wet season from about 12 months of fieldwork. Field observation data combined with mist-net data demonstrate noticeable seasonal changes in certain species’ abundances, indicating (i) seasonal movements out of the montane forest during the dry season and (ii) movements of part of the populations for other species. Our mist-net results show a significant difference in species abundances between the two seasons driven by 16 species. We also document significant changes in diet for two species of greenbuls, which shift feeding behavior from arthropods in the wet season to include a larger proportion of fruit in their dry season diet. Our results further show that birds are more active in mixed-species flocks in the dry season, with a significantly higher average number of species and of individuals in the dry season, i.e., 11.3 (±0.52 SE) species, 32.3 (±1.76 SE) individuals] compared to the wet season 9.7 (±0.78 SE) species, 20.8 (±1.85 SE) individuals]. One of two very distinctive types of mixed-species flocks – confined to the understory – exists only in the dry season. We discuss these changes to seasonal variability in climate, i.e., temperature and precipitation.

We set out to describe the prevalence of Salmonella enterica in three large, adjacent cattle operations in the southern High Plains of the United States. Operations included two dairies (one of which routinely administers a commercially available Salmonella vaccine) and one feedlot. Samples were collected monthly for 12 months. At each sample collection, 25 freshly voided fecal pats and a sample from each of the water troughs were collected from each of five pens of cattle within an operation. Each monthly collection included a total of 375 fecal and ~32 water samples for a yearly total of 4,500 and 379 samples, respectively (note that the number of water troughs per pen varied within an operation). Salmonella was commonly recovered from fecal (71.3%) and water (28.5%) samples and tended to follow somewhat similar temporal patterns over time. However, its prevalence varied among operations despite being adjacent properties in that Salmonella was recovered from 61.3, 80.1, and 75% of fecal samples from dairy 1, dairy 2 and the feedlot, respectively. Salmonella prevalence in water samples across collection times averaged 36.1, 70.2, and 46.1% for dairy 1, dairy 2, and the feedlot, respectively. While it is uncertain why the Salmonella prevalence varied from operation to operation, the higher observed prevalence of Salmonella in water on dairy 2 and/or the use of a commercial Salmonella vaccine by dairy 1 may offer a partial explanation.

Salmonella is a significant food safety concern in commercial beef production, and some contamination is thought to occur by inclusion of Salmonella-infected peripheral lymph nodes (LN) in ground beef and through fecal contamination. Surveillance in processing plants assists packers in risk management of Salmonella by understanding seasonal trends and risks associated with different cattle types. Approximately 25 fecal samples and 20 LN were collected from animals representing each of five cattle types (cull beef cattle, cull dairy cows, conventional feedlot cattle, all-natural feedlot cattle raised without pharmaceuticals, and grass-finished cattle) and each of five climate regions (mixed-temperatures and dry, mixed-temperatures and humid, hot and humid, hot and dry, cold) during each of three seasons (summer, fall, winter) to better characterize Salmonella inputs into a commercial cattle processing facility. In total, 1,840 fecal samples and 1,550 LN samples were collected. Fecal samples and LN were cultured for Salmonella, and select isolates were serogrouped and screened for antimicrobial resistance. Conventional feedlot cattle had the highest LN Salmonella concentrations (1.17 log10 CFU/g LN) in this data set, while cull dairy cows had the highest fecal Salmonella concentrations (1.96 log10 CFU/g feces). Conventional feedlot cattle and cull dairy cows had the greatest Salmonella prevalence in both LN (32 and 18%, respectively) and feces (37 and 49%, respectively), while all-natural feedlot cattle had the lowest prevalence in the LN (3%) and feces (7%). As expected, Salmonella prevalence and concentration was lowest for all cattle types during winter compared to warmer seasons. When examined by climate region, a greater Salmonella prevalence in both feces and LN was observed in climate region 4 (hot-dry), than the other regions. Only 21 of 50 Salmonella isolates examined for antimicrobial susceptibility were identified as multidrug resistant (MDR); cull dairy cows were responsible for 48% of MDR isolates, cull beef cattle were responsible for 38%, and conventional feedlot, grass-fed, and all-natural feedlot cattle were each responsible for 4.8%. These results indicate that different production schemes, season, and climate region may influence which cattle are most likely to introduce Salmonella to the abattoir, allowing for greater risk awareness during the slaughter process.

In social species, such as many primate species, conspecifics can pose a threat and individuals that are socially vigilant can prevent harassment. Many previous studies have focused on the role of agonistic interactions on social vigilance. In a variety of primate species, individuals are more vigilant for aggressive or dominant group members. In contrast, only few studies have investigated whether affiliative relationships also affect social vigilance. These studies revealed that individuals with an affiliative relationship showed lower levels of vigilance towards each other. Here, we tested the differential effects of both dyadic agonism and affiliation on the level of social vigilance of group-living western lowland gorillas (Gorilla gorilla gorilla) at Apenheul Primate Park, The Netherlands. We made continuous focal observations of agonistic and affiliative interactions and we scored level of vigilance during neutral approaches of conspecifics. We found that dyads with many affiliative interactions showed lower levels of vigilance towards each other. The opposite pattern was found for agonistic experiences, but this effect was not statistically robust. In addition, the adult male and adolescent males received higher levels of social vigilance than individuals from other age-sex classes. Our results indicate that level of social vigilance was linked to affiliative and, to a lesser extent, agonistic relationships in western lowland gorillas. We suggest that future studies in both egalitarian and despotic species should investigate whether, next to aggression, affiliation also influences social vigilance.

External stimuli can induce significant changes in the magnetisation of a material; however, these changes can occur very rapidly, making measurements difficult. Herein the authors demonstrate a method of ultrafast magnetometry, enabling the detection of the rapid magnetization changes.

Abstract Background People with migraine have localised (i.e., cephalic) mechanical sensitivity. There is uncertainty regarding widespread (i.e., extra-cephalic) mechanical sensitivity and variations in mechanical sensitivity throughout the migraine cycle. Therefore, this study aimed (1) to comprehensively assess mechanical sensitivity in both cephalic and extra-cephalic regions during the preictal, ictal, postictal and interictal phases; and (2) to compare these findings with mechanical sensitivity at corresponding time-points and locations in healthy participants. Methods According to sample size calculations, 19 people with migraine and 19 matched healthy volunteers participated in a prospective longitudinal study. Pressure pain thresholds were evaluated in three cephalic regions (temporalis, upper trapezius and C1 paraspinal muscles) and two extra-cephalic regions (extensor carpi radialis and tibialis anterior muscle) with a digital algometer during the four phases of the migraine cycle in people with migraine and at corresponding intervals and locations in healthy participants. Linear mixed model analyses with a random intercept were used. Results People with migraine had increased mechanical sensitivity in cephalic and extra-cephalic regions in all phases of the migraine cycle compared to healthy participants. Furthermore, this mechanical sensitivity was more severe in the preictal, ictal and postictal phase compared to the interictal phase in cephalic and extra-cephalic regions. Conclusion People with migraine have localised as well as widespread mechanical sensitivity compared to healthy participants. This sensitivity is even more pronounced immediately before, during and after a migraine attack.

This paper presents an updated geological reconstruction of the Quaternary evolution of the River Thames at its downstream extremities, close to the North Sea coast, based on new data from multi-disciplinary and citizen-science sources. In this area, the interaction of the Thames with the MIS 12 (Anglian) glaciation is an important part of the Quaternary archive. The Anglian ice sheet, which reached parts of north and east London, was responsible for diverting the Thames southwards into its present course, although the footprint of the maximum ice sheet(s) does not reach the North Sea coast south of Hollesley, Suffolk. Further south, the coastal zone hosts pre-Anglian and early Anglian river-terrace deposits of the pre-diversion Thames system, superimposed upon which are products of later post-Anglian rivers, of both Middle and Late Pleistocene age. On the peninsula between the Stour and Blackwater–Colne estuaries, the lowest and most recent terrace of the pre-diversion Thames includes evidence directly pertaining to the glacial disruption event, for which geochronological data are reported here for the first time. The first post-diversion terrace of the Thames also reaches this peninsula, the river having essentially re-joined its original valley before crossing the alignment of the modern coastline. This terrace passes beneath Clacton-on-Sea, where it includes the type locality of the Clactonian Palaeolithic Industry. The area of interest to this paper, in NE Essex and southern Suffolk, includes a number of interglacial and Palaeolithic sites, the data from which assist in constraining the chronostratigraphy of the sequence. In some cases, there has been uncertainty as to whether these sites represent pre-Anglian environments and hominin occupations, part of the palaeo-Thames sequence, or whether they are the product of later post-Anglian streams, formed after the Thames had migrated southwards. This paper compiles evidence from a wide range of recent sources, including developer-funded archaeological appraisal and citizen-science activities, to explore and update the evidence from sites at Ipswich, Upper Dovercourt and Thorpe-le-Soken, as well as a number of localities associated with the Clacton Channel Deposits (host to the type-Clactonian), amongst others. The resulting new data are placed within the wider context of the Quaternary fluvial archives in southern Britain, with a discussion of how disparate sources of information, including the work of citizen scientists, have contributed.

Despite a history dating back to the 1800s, using Clostridium bacteria to treat cancer has not advanced beyond the observation that they can colonise and partially destroy solid tumours. Progress has been hampered by their inability to eradicate the viable portion of tumours, and an instinctive anxiety around injecting patients with a bacterium whose close relatives cause tetanus and botulism. However, recent advances in techniques to genetically engineer Clostridium species gives cause to revisit this concept. This paper illustrates these developments through the attenuation of C. sporogenes to enhance its clinical safety, and through the expression and secretion of an immunotherapeutic. An 8.6 kb sequence, corresponding to a haemolysin operon, was deleted from the genome and replaced with a short non-coding sequence. The resultant phenotype of this strain, named C. sporogenes-NT, showed a reduction of haemolysis to levels similar to the probiotic strain, C. butyricum M588. Comparison to the parental strain showed no change in growth or sporulation. Following injection of tumour-bearing mice with purified spores of the attenuated strain, high levels of germination were detected in all tumours. Very low levels of spores and vegetative cells were detected in the spleen and lymph nodes. The new strain was transformed with four different murine IL-2-expressing plasmids, differentiated by promoter and signal peptide sequences. Biologically active mIL-2, recovered from the extracellular fraction of bacterial cultures, was shown to stimulate proliferation of T cells. With this investigation we propose a new, safer candidate for intratumoral delivery of cancer immunotherapeutics.

Den här artikeln berör situationer då plagiat kan uppstå. Mer specifikt handlar artikeln om studenters färdigheter och förmågor när det kommer till plagiering eller situationer som skulle kunna förstås som plagiering. En enkät med nio olika situationer skapades i syfte att kartlägga studenters förmåga att identifiera när det kan handla om plagiat. 634 studenter på två olika institutioner vid Göteborgs universitet svarade på enkäten. Resultat och analys visar att studenter generellt hade god förmåga att identifiera enklare fall av plagiat, men klarade sig sämre i mer komplexa fall. Resultaten pekar vidare på att det framförallt är yngre studenter (födda på 90-talet) och akademiskt oerfarna som har lägre träffsäkerhet i sin identifikation. Artikeln avslutas med en reflektion kring undervisning och examination och lyfter särskilt fram tre delar: (i) vikten av att prata om plagiat, (ii) vikten av att arbeta med akademisk integritet och (iii) vikten av att arbeta med akademiskt oerfarna.

Abstract Background Central venous catheters (CVCs) are commonly secured with sutures which are associated with microbial colonization and infection. We report a comparison of a suture-free system with standard sutures for securing short-term CVC in an international multicentre, prospective, randomized, non-blinded, observational feasibility study. Consented critical care patients who had a CVC inserted as part of their clinical management were randomized to receive either sutures or the suture-free system to secure their CVC. The main outcome measures were CVC migration (daily measurement of catheter movement) and unplanned catheter removals. Results The per cent of unplanned CVC removal in the two study groups was 2% (suture group 2 out of 86 patients) and 6% (suture-free group 5 out of 85 patients). Both securement methods were well tolerated in terms of skin irritation. The time and ease of application and removal of either securement systems were not rated significantly different. There was also no significant difference in CVC migration between the two securement systems in exploratory univariate and multivariate analyses. Overall, 42% (36 out of 86) of the CVC secured with sutures and 56% (48 out of 85) of the CVC secured with the suture-free securement system had CVC migration of ≥ 2 mm. Conclusions The two securement systems performed similarly in terms of CVC migration and unplanned removal of CVC; however, the feasibility study was not powered to detect statistically significant differences in these two parameters. Trial registration ISRCTN, ISRCTN13939744. Registered 9 July 2015, http://www.isrctn.com/ISRCTN13939744.

Spatial proteomics allows studying cellular protein localisations at system-wide scale. Here, the authors show that combining the previously developed hyperLOPIT method with differential centrifugation yields protein localisation maps at suborganellar resolution while reducing analysis time and input material.

The disposal of unexploded ordnance (UXOs) at sea is a global problem. The mapping and remediation of historic UXOs can be assisted by autonomous underwater vehicles (AUVs) carrying sensor payloads such as synthetic aperture sonar (SAS) and optical cameras. AUVs can image large areas of the seafloor in high resolution, motivating an automated approach to UXO detection. Modern methods commonly use supervised machine learning which requires labelled examples from which to learn. This work investigates the often-overlooked labelling process and resulting dataset using an example historic UXO dumpsite at Skagerrak. A counterintuitive finding of this work is that optical images cannot be relied on for ground truth as a significant number of UXOs visible in SAS images are not in optical images, presumed buried. Given the lack of ground truth, we use an ordinal labelling scheme to incorporate a measure of labeller uncertainty. We validate this labelling regime by quantifying label accuracy compared to optical labels with high confidence. Using this approach, we explore different taxonomies and conclude that grouping objects into shells, bombs, debris, and natural gave the best trade-off between accuracy and discrimination.

Objective This systematic review and meta-analysis aims to systematically analyse the association of overweight and obesity with health service utilisation during childhood.Data sources PubMed, MEDLINE, CINAHL, EMBASE and Web of Science.Methods Observational studies published up to May 2020 that assessed the impact of overweight and obesity on healthcare utilisation in children and adolescents were included. Studies were eligible for inclusion if the included participants were ≤19 years of age. Findings from all included studies were summarised narratively. In addition, rate ratios (RRs) and 95% CIs were calculated in a meta-analysis on a subgroup of eligible studies.Outcome measures Included studies reported association of weight status with healthcare utilisation measures of outpatient visits, emergency department (ED) visits, general practitioner visits, hospital admissions and hospital length of stay.Results Thirty-three studies were included in the review. When synthesising the findings from all studies narratively, obesity and overweight were found to be positively associated with increased healthcare utilisation in children for all the outcome measures. Six studies reported sufficient data to meta-analyse association of weight with outpatient visits. Five studies were included in a separate meta-analysis for the outcome measure of ED visits. In comparison with normal-weight children, rates of ED (RR 1.34, 95% CI 1.07 to 1.68) and outpatient visits (RR 1.11, 95% CI 1.02 to 1.20) were significantly higher in obese children. The rates of ED and outpatient visits by overweight children were only slightly higher and non-significant compared with normal-weight children.Conclusions Obesity in children is associated with increased healthcare utilisation. Future research should assess the impact of ethnicity and obesity-associated health conditions on increased healthcare utilisation in children with overweight and obesity.PROSPERO registration number CRD42018091752

Timing of births in ungulates is influenced by ecological factors, and differences in seasonality of births have evolutionary implications for these mammals. Birthing habitat is one of the most important home-range attributes for ungulates, and disturbances during this time can decrease survival of young and population growth. We calculated timing of births and quantified habitat selected by nursery groups (i.e., females with young) of desert bighorn sheep (Ovis canadensis nelsoni) to produce and project a geographic information system (GIS) model of lambing period habitat (i.e., birthing locations and areas used up to 6 weeks post-parturition) in southeastern Utah, United States. We then applied that model to identify suitable lambing period habitat in an adjacent area for a population of Rocky Mountain bighorn sheep (O. c. canadensis). We monitored 19 global positioning system (GPS) collared females from 2012 to 2013 to delineate the birthing season. We used GPS locations during that time and logistic regression within a model-selection framework to differentiate between lambing period habitat and random locations based on habitat and anthropogenic covariates. We used model coefficients to produce and project a GIS model of lambing period habitat. Across both years, 89% of 45 births occurred in May (range = April 27–June 9). We quantified covariate values at 750 lambing period and 750 random locations during that time in the San Rafael study area. The top model included elevation, slope, terrain ruggedness, aspect, existing vegetation type, and distance to trails and roads. Those variables predicted lambing period habitat for desert bighorn sheep (rho = 0.99, P = 0.02). We then overlaid that model on 1,130 GPS locations from 17 female Rocky Mountain bighorns in the Green River study area. In both areas, a mean of 71% of locations were in the top two (of five) probability categories (San Rafael high = 37%, medium high = 31%; Green River high = 50%, medium high = 23%). Females in lambing period habitat preferred steep, north-facing slopes, rugged terrain, low elevation, and avoided roads. Our GIS model projected areas of lambing period habitat for adjacent desert and Rocky Mountain bighorns and provided land managers with a map of habitat in areas where resource extraction and recreation are increasing. Identifying timing of parturition, and high-probability lambing period habitat, will help managers mitigate temporal and spatial conflicts between bighorn sheep and anthropogenic activities. Similar data regarding timing of births and a GIS model can be applied to conserve habitat for other ungulates also.

Denned polar bears (Ursus maritimus) are invisible under the snow, therefore winter-time petroleum exploration and development activities in northern Alaska have potential to disturb maternal polar bears and their cubs. Previous research determined forward looking infrared (FLIR) imagery could detect many polar bear maternal dens under the snow, but also identified limitations of FLIR imagery. We evaluated the efficacy of FLIR-surveys conducted by oil-field operators from 2004-2016. Aerial FLIR surveys detected 15 of 33 (45%) and missed 18 (55%) of the dens known to be within surveyed areas. While greater adherence to previously recommended protocols may improve FLIR detection rates, the physical characteristics of polar bear maternal dens, increasing frequencies of weather unsuitable for FLIR detections-caused by global warming, and competing false positives are likely to prevent FLIR surveys from detecting maternal dens reliably enough to afford protections consonant with increasing global threats to polar bear welfare.

Probing spin pumping in the terahertz regime allows one to reveal its initial elementary steps. Here, the authors show that the formation of the spin Seebeck current in YIG/Pt critically relies on hot thermalized metal electrons because they impinge on the metal-insulator interface with maximum noise.

Most of the archaeological record of the Middle to Later Stone Age transition comes from southern Africa. Here, Shipton et al. describe the new site Panga ya Saidi on the coast of Kenya that covers the last 78,000 years and shows gradual cultural and technological change in the Late Pleistocene.

Abstract Background The optimal decontamination method for needle-free connectors is still unresolved. The objective of this study was to determine if a continuous passive disinfection cap is as effective as standard cleaning for the microbial decontamination of injection ports of two types of needle-free connectors. Methods The injection ports of needle-free connectors were inoculated with Staphylococcus aureus and allowed to dry. Disinfection caps containing 70% (v/v) isopropyl alcohol (IPA) were attached to the connectors for one, three or 7 days and were compared with needle-free connectors cleaned with 2% (w/v) chlorhexidine gluconate (CHG) in 70% (v/v) IPA. The number of S. aureus remaining on the injection ports was evaluated. Median log10 reductions and 95% confidence interval (CI) were calculated and data analyzed using the Mann-Whitney test. Results The application of the disinfection cap resulted in a significantly higher reduction in S. aureus than the 2% (w/v) CHG in 70% (v/v) IPA wipe, achieving a > 5 Log10 reduction in CFU at each time point. Conclusions The disinfection caps resulted in a significantly higher reduction in S.aureus on the injection ports when compared to the use of a 2% (w/v) CHG in 70% (v/v) IPA wipe. This offers an explanation for the lower rates of central-line associated bloodstream infection (CLABSI) associated with the use of disinfection caps reported in clinical studies.

Electron paramagnetic resonance (EPR) performed with a scanning tunneling microscope (STM) allows for probing the spin excitation of single atomic species with MHz energy resolution. One of the basic applications of conventional EPR is the precise determination of magnetic moments. However, in an STM, the local magnetic fields of the spin-polarized tip can introduce systematic errors in the measurement of the magnetic moments by EPR. We propose to solve this issue by finding tip-sample distances at which the EPR resonance shift caused by the magnetic field of the tip is minimized. To this end, we measure the dependence of the resonance field on the tip-sample distance at different radiofrequencies and identify specific distances for which the true magnetic moment is found. Additionally, we show that the tip's influence can be averaged out by using magnetically bistable tips, which provides a complementary method to accurately measure the magnetic moment of surface atoms using EPR STM.

Although bear-inflicted (Ursus spp.) human fatalities are rare in North America, human injuries, property damage, and bear mortalities occur wherever bears and humans commingle. We investigated the efficacy of portable electric fencing systems for bear deterrence under a variety of environmental conditions in the lab and field. Our results showed that the bear deterrent systems we evaluated were effective in protecting humans, their food, and property from bears >99% of the time. Herein, we discuss the benefits of using electric fencing, reasons why fences sometimes fail, and provide guidance regarding the most effective implementation of the systems we evaluated. Lastly, we also explore why this deterrent is not yet in widespread use. We encourage the use of electric fencing in bear country for protecting humans, their camping gear and food, and ultimately to promote bear conservation.

Objectives: High-resolution prostate imaging may allow for detection of subtle changes in tumor size, decrease the reliance on biopsies, and help define tumor boundaries during ablation. This pilot clinical trial evaluates a novel high-resolution prostate MRI for detection of small, biopsy-proven prostate tumors. Methods: Our team developed a software that can be loaded on any modern MRI to generate high resolution diffusion-weighted imaging sequences (HR-DWI), which were compared to standard diffusion-weighted imaging sequence (S-DWI) in a prospective pilot trial in active surveillance patients. HR-DWI captures the entire volume of the prostate rather than sections, reducing streaking artifacts and geometric distortions. Multiple shots, rather than single shots, are used to differentiate signal and noise, enhancing resolution. All images were read by two radiologists. The primary outcome was the percent of biopsy-proven zones seen in 17 patients. The trial was powered to detect discordant proportions of 0.04 and 0.40 at one-sided alpha = 0.05. Results: The resolution was defined using standard phantoms. HR-DWI produced a 5-fold improvement in spatial resolution when compared to S-DWI. Multiparametric (MP)-MRI incorporating S-DWI was useful for predicting biopsy results (AUC 0.72, Fisher's exact p

The morphology of carbon nanotube (CNT) films is an important factor in the performance of CNT/silicon (CNT/Si) heterojunction solar devices. Films have generally been prepared via vacuum filtration from aqueous suspensions. Whilst this enables strong films to be formed quickly, they are highly disordered on the micron scale, with many charge traps and gaps forming in the films. It has been previously established that lowering the filtration speed enables more ordered films to be formed. The use of slow gravity filtration to improve the morphology of CNT films used in the CNT/Si device is reported here. It was found that slow filtration causes significant macroscale inhomogeneity in the CNT films, with concentrated thick regions, surrounded by larger thinner areas. By using atomic force microscopy (AFM), scanning electron microscopy (SEM), and polarised Raman spectroscopy, it was determined that there was no large improvement in directional organisation of the CNTs on the microscale. However, the films were found to be much smoother on the microscale, with arithmetic and root mean square average height deviation values roughly 3 times lower for slow-filtered films compared to fast-filtered films. A comparison was performed with CNT-Si solar cells fabricated with both slow and fast-filtered single-walled CNTs (SWCNT) films. It was found that slow filtration can produce similar photovoltaic results with thinner films. The results demonstrate that film morphology, even without improved CNT alignment, can lead to significant improvement in device performance in some applications. However, slow filtration did not form films of uniform light transmittance over an extended area, causing an increase in the variation in performance between individual devices compared to fast-filtered films.

Adaptation of antibody-mediated immunity occurs in germinal centers (GC). It is where affinity maturation, class switching, memory and plasma cell differentiation synergize to generate specific high-affinity antibodies that aid both to clear and protect against reinfection of invading pathogens. Within GCs, light and dark zone are two compartments instrumental in regulating this process, by segregating T cell-dependent selection and differentiation from generation of GC B cells bearing hypermutated antigen receptors. Spatial segregation of GC B cells into the two zones relies on the chemokine receptor CXCR4, with textbooks attributing high and low expression to a dark and light zone phenotype. Interestingly, this bipolarity is not reflected in the CXCR4 expression profile of GC B cells, which is highly variable and unimodal, indicating a continuum of intermediate CXCR4 levels rather than a binary dark or light zone phenotype. Here, analysis of published BrdU pulse-chase data reveals that throughout cell cycle, average CXCR4 expression in GC B cells steadily increases close to twofold, scaling with cell surface area. CXCR4 expression in recently divided GC B cells in G0/G1 or early S phase shows intermediate levels compared to cells in G2M phase, consistent with their smaller size. The lowest number of CXCR4 receptors are displayed by relatively aged GC B cells in G0/G1 or early S phase. The latter, upon progressing through S phase, however, ramp up relative CXCR4 expression twice as much as recently divided cells. Twelve hours after the BrdU pulse, labeled GC B cells, while initially in S phase, are desynchronized in terms of cell cycle and match the CXCR4 profile of unlabeled cells. A model is discussed in which CXCR4 expression in GC B cell increases with cell cycle and cell surface area, with highest levels in G2 and M phase, coinciding with GC B cell receptor signaling in G2 and immediately preceding activation-induced cytidine deaminase (AID) activity in early G1. In the model, GC B cells compete for CXCL12 expression on the basis of their CXCR4 expression, gaining a relative advantage as they progress in cell cycle, but loosing the advantage at the moment they divide.