Mixture models for distance sampling detection functions

Funding: EPSRC DTGWe present a new class of models for the detection function in distance sampling surveys of wildlife populations, based on finite mixtures of simple parametric key functions such as the half-normal. The models share many of the features of the widely-used “key function plus series adjustment” (K+A) formulation: they are flexible, produce plausible shapes with a small number of parameters, allow incorporation of covariates in addition to distance and can be fitted using maximum likelihood. One important advantage over the K+A approach is that the mixtures are automatically monotonic non-increasing and non-negative, so constrained optimization is not required to ensure distance sampling assumptions are honoured. We compare the mixture formulation to the K+A approach using simulations to evaluate its applicability in a wide set of challenging situations. We also re-analyze four previously problematic real-world case studies. We find mixtures outperform K+A methods in many cases, particularly spiked line transect data (i.e., where detectability drops rapidly at small distances) and larger sample sizes. We recommend that current standard model selection methods for distance sampling detection functions are extended to include mixture models in the candidate set.Publisher PDFPeer reviewe

Mark-Recapture and Stochastic Population Models for Polar Bears of the High Arctic

We used mark-recapture data and population viability analysis (PVA) to estimate demographic parameters, abundance, and harvest risks for two adjacent populations of polar bears (Ursus maritimus) inhabiting Lancaster Sound and Norwegian Bay, Canada. Analyses were based on data from 1871 bears that were uniquely marked during the period 1972–97. Our best-fitting mark-recapture model specified sex and age effects on probabilities of survival and an effect of prior recapture (dependence) on capture probability. The most parsimonious solution in our analysis of survival was to assume the same rate for the Lancaster Sound and Norwegian Bay populations. Total (harvested) annual survival rates (mean ± 1 SE) for females included: 0.749 ± 0.105 (cubs), 0.879 ± 0.050 (ages 1–4), 0.936 ± 0.019 (ages 5– 20), and 0.758 ± 0.054 (ages 21+). Mean litter size was 1.69 ± 0.01 cubs for females of Lancaster Sound and 1.71 ± 0.08 cubs for females of Norwegian Bay. By age six, on average 0.31 ± 0.21 females of Lancaster Sound were producing litters (first age of reproduction was five years); however, females of Norwegian Bay did not reproduce until age seven or more. Total abundance (1995–97) averaged 2541 ± 391 bears in Lancaster Sound and 203 ± 44 bears in Norwegian Bay. The finite rate of increase (lambda) during the study period was estimated to be 1.001 ± 0.013 for bears of Lancaster Sound and 0.981 ± 0.027 for bears of Norwegian Bay. We incorporated demographic parameters into a harvest-explicit PVA to model short-term (15 yr) probabilities of overharvesting (i.e., 1997–2012). Our harvest simulations suggest that current levels of kill are approaching and perhaps exceeding the sustainable yield in both populations.Nous avons recouru aux données obtenues par marquage et recapture ainsi qu’aux analyses de viabilité de population pour estimer les paramètres démographiques, l’abondance et les risques liés à la récolte de deux populations adjacentes d’ours polaires (Ursus maritimus) évoluant dans le détroit de Lancaster et la baie Norwegian, au Canada. Les analyses reposaient sur les données relatives à 1 871 ours marqués de manière unique pendant la période allant de 1972 à 1997. Notre modèle de marquage et recapture le mieux ajusté tenait compte des effets du sexe et de l’âge sur les probabilités de survie, ainsi que de l’effet d’une recapture antérieure (dépendance) sur la probabilité de capture. La solution la plus parcimonieuse de notre analyse de survie consistait à assumer le même taux pour les populations du détroit de Lancaster et de la baie Norwegian. Les taux totaux de survie annuels (récoltés) (moyenne ± 1 SE) chez les femelles s’établissaient comme suit : 0,749 ± 0,105 (oursons), 0,879 ± 0,050 (âges 1-4), 0,936 ± 0,019 (âges 5-20), et 0,758 ± 0,054 (âges 21+). La grosseur moyenne des portées était de 1,69 ± 0,01 ourson dans le cas des femelles du détroit de Lancaster, et de 1,71 ± 0,08 ourson dans le cas des femelles de la baie Norwegian. Avant l’âge de six ans, en moyenne 0,31 ± 0,21 femelle du détroit de Lancaster produisait des portées (l’âge de reproduction le plus jeune était de cinq ans); cependant, les femelles de la baie Norwegian ne se reproduisaient pas avant l’âge de sept ans ou plus. L’abondance totale (1995-1997) atteignait en moyenne 2 541 ± 391 ours au détroit de Lancaster, et 203 ± 44 ours dans la baie Norwegian. Le taux fini d’augmentation (lambda) pendant la période d’étude était estimé à 1,001 ± 0,013 dans le cas des ours du détroit de Lancaster, et de 0,981 ± 0,027 dans le cas des ours de la baie Norwegian. Nous avons intégré les paramètres démographiques à une analyse de viabilité de population de récolte explicite pour modéliser les probabilités à court terme (15 ans) de surrécolte (i.e. 1997-2012). Nos simulations de récolte laissent croire que les taux d’ours tués approchent et peuvent même dépasser le rendement admissible des deux populations

High adherence to the nordic diet is associated with lower levels of total and platelet-derived circulating microvesicles in a norwegian population

Circulating microvesicles (cMV) are small phospholipid-rich blebs shed from the membrane of activated vascular cells that contribute to vascular disease progression. We aimed to investigate whether the quality of the Nordic diet is associated with the degree of blood and vascular cell activation measured by MV shedding in elderly patients after an acute myocardial infarction (AMI). One-hundred and seventy-four patients aged 70-82 years were included in this cross-sectional study. Fasting blood samples were taken within 2 to 8 weeks after an AMI. Annexin V (AV) cMV derived from blood and vascular cells were measured through flow cytometry. A patient's usual diet was recorded with the SmartDiet® questionnaire. Patients with higher adherence to the Nordic diet (highest diet score) had lower levels of total AV and platelet-derived (CD61/AV and CD31/AV) cMV. Dietary habits influence cellular activation. A high adherence to the Nordic diet (assessed by the SmartDiet® score) in elderly post-AMI patients was associated with lower levels of platelet activation, which was reflected by a lesser release of MV carrying platelet-derived epitopes, potentially contributing to an explanation of the cardioprotective effects of the Nordic diet

Screening breast cancer patients for Norwegian ATM mutations

483 Norwegian breast cancer patients were screened for six different ataxia telangiectasia mutated (ATM) mutations previously found to account for 83% of the disease alleles in Norwegian ataxia telangiectasia (AT) patients. Only one carrier was found. These results provide no evidence in favour of an excess risk of breast cancer associated with heterozygosity for classical AT mutations, but remain consistent with a maximum 2.4-fold increased risk. © 2000 Cancer Research Campaign http://www.bjcancer.co

Demography and Viability of a Hunted Population of Polar Bears

We estimated demographic parameters and harvest risks for a population of polar bears (Ursus maritimus) inhabiting Baffin Bay, Canada and Greenland, from 1974 to 1997. Our demographic analysis included a detailed assessment of age- and sex-specific survival and recruitment from 1221 marked polar bears, which used information contained within the standing age distribution of captures and mark-recapture analysis performed with Program MARK. Unharvested (natural) survival rates for females (± 1 SE) from mark-recapture analysis were 0.620 ± 0.095 (cubs), 0.938 ± 0.042 (ages 1–4), 0.953 ± 0.020 (ages 5–20), and 0.919 ± 0.046 (ages 21+). Total (harvested) survival rates for females were reduced to 0.600 ± 0.096 (cubs), 0.901 ± 0.045 (ages 1–4), 0.940 ± 0.021 (ages 5–20), and 0.913 ± 0.047 (ages 21+). Mean litter size was 1.59 ± 0.07 cubs, with a mean reproductive interval of 2.5 ± 0.01 years. By age 5, on average 0.88 ± 0.40 of females were producing litters. We estimated the geometric means (± bootstrapped SDs) for population growth rates at stable age distribution as 1.055 ± 0.011 (unharvested) and 1.019 ± 0.015 (harvested). The model-averaged, mark-recapture estimate of mean abundance (± 1 SE) for years 1994–97 was 2074 ± 266 bears, which included 1017 ± 192 females and 1057 ± 124 males. We incorporated demographic parameters and their error terms into a harvest risk analysis designed to consider demographic, process, and sampling uncertainty in generating likelihoods of persistence (i.e., a stochastic, harvest-explicit population viability analysis). Using our estimated harvest of polar bears in Baffin Bay (88 bears/yr), the probability that the population would decline no more than could be recovered in five years was 0.95, suggesting that the current hunt is sustainable.De 1974 à 1997, on a évalué les paramètres démographiques d’une population d’ours polaires (Ursus maritimus) habitant la baie de Baffin (Canada et Groenland), ainsi que les risques associés à leur prélèvement. Notre analyse démographique comprenait un bilan détaillé de la survie et du recrutement par âge et par sexe, bilan mené sur 1221 ours polaires étiquetés et qui faisait appel à l’information contenue dans les limites de la structure d’âge des captures à un moment précis, ainsi que des analyses de marquage-recapture réalisées avec le logiciel MARK. Les taux de survie sans prélèvements (c’est-à-dire naturels) des femelles (± 1 erreur-type) tirés de l’analyse de marquage-recapture étaient les suivants: 0,620 ± 0,095 (oursons), 0,938 ± 0,042 (1–4 ans), 0,953 ± 0,020 (5–20 ans) et 0,919 ± 0,046 (21 ans et plus). Les taux de survie globaux (avec prélèvements) des femelles diminuaient à: 0,600 ± 0,096 (oursons), 0,901 ± 0,045 (1–4 ans), 0,940 ± 0,021 (5–20 ans) et 0,913 ± 0,047 (21 ans et plus). La taille moyenne des portées était de 1,59 ± 0,07 ourson avec des intervalles moyens de reproduction de 2,5 ± 0,01 ans. Arrivées à l’âge de cinq ans, en moyenne 0,88 ± 0,40 des femelles avaient eu des petits. On a évalué que les moyennes géométriques (± écart-type bootstrappé) pour les taux de croissance de la population à la structure d’âge stable étaient de 1,055 ± 0,011 (sans prélèvements) et de 1,019 ± 0,015 (avec prélèvements). La valeur estimée à partir du marquage-recapture, moyennée par le modèle, de l’abondance moyenne (± 1 erreur-type), pour les années allant de 1994 à 1997 était de 2074 ± 266 ours, dont 1017 Å} 192 femelles et 1057 ± 124 mâles. On a intégré les paramètres démographiques et leurs termes d’erreur dans une analyse des risques de prélèvements conçue pour tenir compte des incertitudes démographiques, de processus et d’échantillonnage lors du calcul des probabilités de persistance (c.-à-d. une analyse stochastique de la viabilité de la population qui tient compte des prélèvements). En se basant sur nos prélèvements estimés de l’ours polaire dans la baie de Baffin (88 ours/an), la probabilité que la population ne décline pas plus que ce qu’elle pourrait récupérer en 5 ans était de 0,95, ce qui suggère que la chasse actuelle est durable

Extracellular matrix formation after transplantation of human embryonic stem cell-derived cardiomyocytes

Transplantation of human embryonic stem cell-derived cardiomyocytes (hESC-CM) for cardiac regeneration is hampered by the formation of fibrotic tissue around the grafts, preventing electrophysiological coupling. Investigating this process, we found that: (1) beating hESC-CM in vitro are embedded in collagens, laminin and fibronectin, which they bind via appropriate integrins; (2) after transplantation into the mouse heart, hESC-CM continue to secrete collagen IV, XVIII and fibronectin; (3) integrin expression on hESC-CM largely matches the matrix type they encounter or secrete in vivo; (4) co-transplantation of hESC-derived endothelial cells and/or cardiac progenitors with hESC-CM results in the formation of functional capillaries; and (5) transplanted hESC-CM survive and mature in vivo for at least 24 weeks. These results form the basis of future developments aiming to reduce the adverse fibrotic reaction that currently complicates cell-based therapies for cardiac disease, and to provide an additional clue towards successful engraftment of cardiomyocytes by co-transplanting endothelial cells

Effectiveness of mRNA booster vaccination against mild, moderate, and severe COVID-19 caused by the Omicron variant in a large, population-based, Norwegian cohort

Background Understanding how booster vaccination can prevent moderate and severe illness without hospitalization is crucial to evaluate the full advantage of mRNA boosters. Methods We followed 85 801 participants (aged 31–81 years) in 2 large population-based cohorts during the Omicron BA.1/2 wave. Information on home testing, PCR testing, and symptoms of coronavirus disease 2019 (COVID-19) was extracted from biweekly questionnaires covering the period 12 January 2022 to 7 April 2022. Vaccination status and data on previous SARS-CoV-2 infection were obtained from national registries. Cox regression was used to estimate the effectiveness of booster vaccination compared to receipt of 2-dose primary series >130 days previously. Results The effectiveness of booster vaccination increased with increasing severity of COVID-19 and decreased with time since booster vaccination. The effectiveness against severe COVID-19 was reduced from 80.9% shortly after booster vaccination to 63.4% in the period >90 days after vaccination. There was hardly any effect against mild COVID-19. The effectiveness tended to be lower among subjects aged ≥60 years than those aged <50 years. Conclusions This is the first population-based study to evaluate booster effectiveness against self-reported mild, moderate, and severe COVID-19. Our findings contribute valuable information on duration of protection and thus timing of additional booster vaccinations.publishedVersio

Waiting list mortality and the potential of donation after circulatory death heart transplantations in the Netherlands

BACKGROUND: With more patients qualifying for heart transplantation (HT) and fewer hearts being transplanted, it is vital to look for other options. To date, only organs from brain-dead donors have been used for HT in the Netherlands. We investigated waiting list mortality in all Dutch HT centres and the potential of donation after circulatory death (DCD) HT in the Netherlands. METHODS: Two different cohorts were evaluated. One cohort was defined as patients who were newly listed or were already on the waiting list for HT between January 2013 and December 2017. Follow-up continued until September 2018 and waiting list mortality was calculated. A second cohort of all DCD donors in the Netherlands (lung, liver, kidney and pancreas) between January 2013 and December 2017 was used to calculate the potential of DCD HT. RESULTS: Out of 395 patients on the waiting list for HT, 196 (50%) received transplants after a median waiting time of 2.6 years. In total, 15% died while on the waiting list before a suitable donor heart became available. We identified 1006 DCD donors. After applying exclusion criteria and an age limit of 50 years, 122 potential heart donors remained. This number increased to 220 when the age limit was extended to 57 years. CONCLUSION: Waiting list mortality in the Netherlands is high. HT using organs from DCD donors has great potential in the Netherlands and could lead to a reduction in waiting list mortality. Cardiac screening will eventually determine the true potential

Listing criteria for heart transplantation in the Netherlands

The updated listing criteria for heart transplantation are presented on behalf of the three heart transplant centres in the Netherlands. Given the shortage of donor hearts, selection of those patients who may expect to have the greatest benefit from a scarce societal resource in terms of life expectancy and quality of life is inevitable. The indication for heart transplantation includes end-stage heart disease not remediable by more conservative measures, accompanied by severe physical limitation while on optimal medical therapy, including ICD/CRT‑D. Assessment of this condition requires cardiopulmonary stress testing, prognostic stratification and invasive haemodynamic measurements. Timely referral to a tertiary centre is essential for an optimal outcome. Chronic mechanical circulatory support is being used more and more as an alternative to heart transplantation and to bridge the progressively longer waiting time for heart transplantation and, thus, has become an important treatment option for patients with advanced heart failure