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Researching sexual and reproductive behaviour: a peer ethnographic approach.

In recent years, ethnographic research has challenged the notion within demography that fertility-related behaviour is the outcome of individualistic calculations of the costs and benefits of having children. Anthropology has further criticised the abstraction in demographic analysis of sexual behaviour and fertility decision-making from the socio-cultural and political context in which the individual or couple is located. Within demography itself, institutional and political-economic analyses have argued strongly that sexual and reproductive behaviour must be understood within locally specific social, cultural, economic and political contexts. Positivist and empiricist research methods, such as the sample survey and focus groups, which continue to dominate demographic inquiry and applied research into sexual and reproductive behaviour, have been shown to be limited in their ability to inform about the process of behaviour change and contexts within which different behaviours occur. The article introduces a new methodology for researching sexual and reproductive behaviour, called the peer ethnographic approach, which the authors have developed in an attempt to address some of the limitations of the methods which currently dominate research into sexual and reproductive behaviour. The peer ethnographic methodology is discussed in detail and the results of recent field-testing are reported, which show that, although the approach has limitations, it also has the potential to make a significant contribution to our understanding of sexual and reproductive behaviour.

Adolescent↗

Environmental effects on age-dependent mortality: a test with a perennial plant species under natural and protected conditions.

Most experimental studies of senescence have been done with short-lived organisms under controlled laboratory conditions and it is not clear whether the insights gained from these studies can be broadly generalized. This study was designed to detect senescence in a natural population and to compare the patterns of mortality for a single species in natural and protected conditions. It was done with Plantago lanceolata, a perennial plant for which the demography of a large population of individuals in their natural environment is relatively straightforward. An initial cohort of 10,000 individuals was established in the natural field environment. In order to separate the effects of environment- and age-dependent factors on mortality, an additional cohort was planted in the field one year later. To study the demography of mortality under protected conditions, a population of 1000 individuals was established in the greenhouse. The results of the comparative analysis of two different-aged cohorts in the field and of the field and greenhouse populations show that senescence patterns can be very plastic. The results show that senescence in the natural environment is caused by an increased vulnerability of older individuals to environmental stress. Under the protected environmental conditions of the greenhouse senescence was negligible.

Ecosystem↗

Oesophageal acid-peptic strictures in the histamine H2 receptor antagonist and proton pump inhibitor era.

BACKGROUND AND AIM: We present a survey on the incidence, demography and natural history (re-dilatation rates) of patients with oesophageal acid-peptic stricture seen between 1977 and 1995. PATIENTS AND METHODS: Prospective, cohort observational study. Stricture severity was graded mild, moderate or severe (needing forcible dilatation with bougies). Most were treated with histamine H2 receptor antagonists or proton pump inhibitors, and were followed up by serial check endoscopy. RESULTS: A total of 156 of 7429 (2%) reflux patients had stricture: mild, n=56; moderate, n=25; severe, n=75. The prevalence of reflux disease is rising, paralleled by an increase in the number of patients with stricture; hence the incidence of stricture is unchanged: 1977-1982, 1.8% (18/986); 1983-1989, 2.4% (61/2595); 1990-1995, 2% (77/3848). Demography: mean age 68 years; mean length of reflux history 6.4 years; 15% on non-steroidal anti-inflammatory drugs/aspirin; 18% with Barrett's metaplasia. Mean follow-up: 5.6 years. OUTCOME: of the 75 with severe stricture, 36 (48%) needed forcible dilatation only once, and 39 more often (13 twice, nine three times), most within 2 years. Only six of these patients need > or = 6 re-dilatations. CONCLUSION: The incidence of stricture is low and remains unchanged, despite the increased prevalence of reflux disease. Most patients have a good prognosis, only half needing further forcible dilatation, mainly within the first 2 years.

Adult↗

Antibodies to Ro/La, Cenp-B, and snRNPs antigens in autoimmune hepatitis of North America versus Asia: patterns of immunofluorescence, ELISA reactivities, and HLA association.

To assess whether demography is one of the important factors determining antibody response to nuclear antigens [ANA: SSA-Ro (52K and 60K), SSB-La, snRNPs (A, 70K, B'/B), and Cenp-B], we investigated 95 and 47 sera of autoimmune hepatitis (AIH) from North America and Asia, respectively, by immunofluorescent (IF) and recombinant ELISA. Correlations among nuclear IF patterns, ELISA, and disease indices were analyzed. The frequency and titer of individual antibodies differed significantly between the groups. Patients with speckled patterns were younger in both regions and had higher aspartate aminotransferase levels only in North America. HLA-A1, B8, DQ2, and DR4 or DR3 or both in North America, and A2, B61, DQ7, and DR4 in Asia were predominant. In Asia, B61 correlated with anti-70K, and DQ7 correlated with antibodies to 52K, Cenp-B, and B'/B. In North America, A1, B8, DR3 haplotype, and DQ2 correlated with antibodies to A and 70K. Anti-B'/B and DR4 in North America, and A2 in Asia, were associated with concurrent immunologic disorder. Individual ANA clusters correlated with individual HLA in the demography, and different HLA alleles might determine disease expression as well as different ANA being produced in AIH.

Adult↗

The age context of performance-evaluation decisions.

Organizational demography contends that demographic characteristics of individuals, examined at individual, dyadic, group, and organizational levels of analysis, exert significant effects on organizational processes. The purpose of this article was to test the contextual effects created by the interaction of work-group age composition and supervisor age on supervisor evaluations of subordinate performance. Two competing models of age demography were tested. The similarity model predicts that supervisors similar in age to the work group they supervise will issue generally higher performance ratings. The dissimilarity model, developed in this article, predicts the opposite. Support was indicated for the dissimilarity model. Implications of the results are discussed.

Adult↗

The effective size of the Icelandic population and the prospects for LD mapping: inference from unphased microsatellite markers.

Characterizing the extent of linkage disequilibrium (LD) in the genome is a pre-requisite for association mapping studies. Patterns of LD also contain information about the past demography of populations. In this study, we focus on the Icelandic population where LD was investigated in 12 regions of approximately 15 cM using regularly spaced microsatellite loci displaying high heterozygosity. A total of 1753 individuals were genotyped for 179 markers. LD was estimated using a composite disequilibrium measure based on unphased data. LD decreases with distance in all 12 regions and more LD than expected by chance can be detected over approximately 4 cM in our sample. Differences in the patterns of decrease of LD with distance among genomic regions were mostly due to two regions exhibiting, respectively, higher and lower proportions of pairs in LD than average within the first 4 cM. We pooled data from all regions, except these two and summarized patterns of LD by computing the proportion of pairs of loci exhibiting significant LD (at the 5% level) as a function of distance. We compared observed patterns of LD with simulated data sets obtained under scenarios with varying demography and intensity of recombination. We show that unphased data allow to make inferences on scaled recombination rates from patterns of LD. Patterns of LD in Iceland suggest a genome-wide scaled recombination rate of rho* = 200 (130-330) per cM (or an effective size of roughly 5000), in the low range of estimates recently reported in three populations from the HapMap project.

Biological Evolution↗

Demographics of enuresis patients attending a referral centre.

OBJECTIVE: To study and compare the demography of enuretic children 7-16 years old attending a tertiary referral centre for childhood urinary incontinence, with that of normal children and what is generally known about enuretics from population-based studies. METHODS AND MATERIALS: This was a retrospective analysis of data compiled from 298 enuretic patients referred to The Centre of Child Incontinence, Aarhus University Hospital, Skejby, Denmark, and 53 healthy controls. Data was obtained by conducting standardised questionnaire interviews. Patients were stratified according to accompanying symptoms and severity of enuresis. Statistical analysis of the results was then performed. RESULTS: Two hundred and ninety-three patients had sufficient data registered to allow reliable analysis. Male-female ratio was 2.2:1. Primary and secondary enuresis was found in 87.4% and 11.6% of the patients respectively. Enuresis was associated with a reported history of bronchial asthma (p < 0.05), verified allergy (p < 0.05) and a positive family history of the same disorder (p < 0.01). No association with psycho-developmental factors was evident. Approximately 98% of the patients had undergone some form of therapy at presentation. 74.1% of the patients had pure monosymptomatic enuresis, 16.4% had day and night time incontinence, while the remaining 9.6% had nocturnal incontinence combined with other lower urinary tract symptoms other than daytime wetting. CONCLUSIONS: The demography of our patient population was, with a few exceptions, within the confines of what has previously been reported. Our results also reaffirmed the heterogeneity of enuretic patients.

Adolescent↗

Evolution of virulence of a plant RNA virus in developmental stage-structured host populations.

Natural host populations are age-structured, and developmental stages differ in susceptibility and within-host pathogen dynamics, potentially imposing distinct selective pressures on viruses. However, the evolutionary consequences of host age structure remain poorly understood. We experimentally evolved turnip mosaic potyvirus for 5 passages in Arabidopsis thaliana populations spanning 7 demographic regimes, from juvenile- to mature-dominated cohorts. We quantified disease progression, symptom severity, and viral load, cross-inoculated evolved lineages across host stages to construct infection matrices, and performed whole-population sequencing at passages 1 and 5. Disease traits changed markedly with passage, demography, and their interaction. Disease progression evolved faster in older populations, whereas symptom severity was independent of median age, indicating demographic reweighting of virulence components. Viral load increased across passages and positively correlated with severity, linking within-host fitness to symptoms. Cross-inoculation assays revealed a modular infection network: juvenile-evolved lineages specialized on juvenile hosts, whereas lineages from intermediate and older populations were more generalist. Genomically, we detected both parallel and demography-specific adaptations, including recurrent changes in the viral protein VPg (involved in translation, replication, and host interactions) as well as synonymous variants showing consistent or opposing selection across host population stage structures. Overall, host age structure emerges as a major ecological driver of virulence evolution, shaping tradeoffs between disease progression and severity and determining specialization versus generalism. These results integrate phenotypic and genomic responses and suggest that manipulating crop age structure could steer virus evolution toward less damaging outcomes.

Virulence↗

Balancing food and predator pressure induces chronic stress in songbirds.

The never-ending tension between finding food and avoiding predators may be the most universal natural stressor wild animals experience. The 'chronic stress' hypothesis predicts: (i) an animal's stress profile will be a simultaneous function of food and predator pressures given the aforesaid tension; and (ii) these inseparable effects on physiology will produce inseparable effects on demography because of the resulting adverse health effects. This hypothesis was originally proposed to explain synergistic (inseparable) food and predator effects on demography in snowshoe hares (Lepus americanus). We conducted a 2 x 2, manipulative food addition plus natural predator reduction experiment on song sparrows (Melospiza melodia) that was, to our knowledge, the first to demonstrate comparable synergistic effects in a bird: added food and lower predator pressure in combination produced an increase in annual reproductive success almost double that expected from an additive model. Here we report the predicted simultaneous food and predator effects on measures of chronic stress in the context of the same experiment: birds at unfed, high predator pressure (HPP) sites had the highest stress levels; those at either unfed or HPP sites showed intermediate levels; and fed birds at low predator pressure sites had the lowest stress levels.

Analysis of Variance↗

Predictors of early survival in Soay sheep: cohort-, maternal- and individual-level variation.

A demographic understanding of population dynamics requires an appreciation of the processes influencing survival--a demographic rate influenced by parameters varying at the individual, maternal and cohort level. There have been few attempts to partition the variance in demography contributed by each of these parameter types. Here, we use data from a feral population of Soay sheep (Ovis aries), from the island of St Kilda, to explore the relative importance of these parameter types on early survival. We demonstrate that the importance of variation occurring at the level of the individual, and maternally, far outweighs that occurring at the cohort level. The most important variables within the individual and maternal levels were birth weight and maternal age class, respectively. This work underlines the importance of using individual based models in ecological demography and we, therefore, caution against studies that focus solely on population processes.

Animals↗

A model for background selection in non-equilibrium populations.

In many taxa, levels of genetic diversity are observed to vary along their genome. The framework of background selection models this variation in terms of linkage to constrained sites, and recent applications have been able to explain a large portion of the variation in human genomes. However, these studies have also yielded conflicting results, stemming from two key limitations. First, existing models are inaccurate in a critical region of parameter space (), where the local reduction in diversity is sharpest. Second, they assume a constant population size over time. Here, we develop predictions for diversity under background selection based on the Hill-Robertson system of two-locus statistics, which allows for population size changes. We treat the joint effect of multiple selected loci independently, but we show that interference among them is well captured through local rescaling of mutation, recombination and selection in an iterative procedure that converges quickly. We further accommodate existing background selection theory to non-equilibrium demography, bridging the gap between weak and strong selection. Simulations show that our predictions are accurate across the entire range of selection coefficients. We characterize the temporal dynamics of linked selection under population size changes and demonstrate that patterns of diversity can be misinterpreted by other models. Specifically, biases due to the incorrect assumption of equilibrium carry over to downstream inferences of the distribution of fitness effects and deleterious mutation rate. Jointly modeling demography and linked selection therefore improves our understanding of the genomic landscape of diversity, which will help refine inferences of linked selection in humans and other species.

Journal Article↗

Determinants of prescribing patterns for type II diabetes at Primary Care Trust level.

OBJECTIVE: To estimate the effect of demography, deprivation and ethnicity on variations in prescribing of oral antidiabetics at the Primary Care Trust level. DESIGN: Cross-sectional survey. SETTING: All Primary Care Trusts in England. MAIN OUTCOME MEASURES: Percentage of variance explained. RESULTS: A model using measures of demography, ethnicity, deprivation and use of thiazolidinediones explained 59% of the variation in cost per registered patient although individual variables explained far less. CONCLUSIONS: This study shows the importance of using a multivariate approach in modelling the drivers of cost. The high use of thiazolidinediones is of concern in the light of NICE guidance.

Cross-Sectional Studies↗

Genetics of cattails in radioactively contaminated areas around Chornobyl.

Research on populations from radioactively contaminated areas around Chornobyl has produced ambiguous results for the presence of radiation effects. More studies are needed to provide information on whether radiation exposure at Chornobyl significantly affected genetic diversity in natural populations of various taxa. Eleven and nine variable microsatellite loci were used to test for differences in genetic diversity between reference and Chornobyl populations of two cattail species (Typha angustifolia and Typha latifolia, respectively) from Ukraine. Our purpose was to determine whether radiation had a significant impact on genetic diversities of the Chornobyl Typha populations, or if their genetic composition might be better explained by species demography and/or changes in population dynamics, mainly in sexual and asexual reproduction. Populations closest to the reactor had increased genetic diversities and high number of genets, which likely were due to factors other than radiation including increased gene flow among Chornobyl populations, enhanced sexual reproduction within populations, and/or origin of the genets from seed bank. Both Typha species also demonstrated small but significant effects associated with latitude, geographical regions, and watersheds. Typha's demography in Ukraine possibly varies with these three factors, and the small difference between Chornobyl and reference populations of T. latifolia detected after partitioning the total genetic variance between them is probably due primarily to these factors. However, the positive correlations of several genetic characteristics with radionuclide concentrations suggest that radiation may have also affected genetics of Chornobyl Typha populations but much less than was expected considering massive contamination of the Chornobyl area.

Alleles↗

Patterns of genetic connectivity among anchialine habitats: a case study of the endemic Hawaiian shrimp Halocaridina rubra on the island of Hawaii.

Anchialine habitats, landlocked bodies of mixohaline water that fluctuate with the tides but have no surface connection to the sea, are known from around the world. Many anchialine organisms have widespread distributions and it has been hypothesized that high levels of gene flow and low levels of genetic differentiation are characteristic of populations from these habitats. However, the generality of this hypothesis requires further assessment, particularly in light of the significant negative impact these habitats and their biota have experienced from anthropogenic causes. This study investigated the population structure and demography of an endemic Hawaiian anchialine species, the atyid shrimp Halocaridina rubra, using mitochondrial cytochrome c oxidase subunit I (COI) gene sequences. A survey of 305 individuals from 16 populations collected on the island of Hawaii revealed 135 haplotypes. These haplotypes belonged to one of two divergent (2.7-4.9%) lineages; notably, no haplotypes were shared between the two coasts of the island. Along each coast, strong subdivision and little to no gene flow occurs between populations separated by > 30 km. The population structure and demography of H. rubra on Hawaii are influenced by regional hydrology, geology, volcanism and two distinct colonization events of the island. Thus, H. rubra on Hawaii demonstrates that populations of endemic anchialine organisms may exhibit significant levels of genetic structure and restricted levels of gene flow over limited geographic scales. This report brings novel insight into the biology of anchialine organisms and has important implications for the future management of these habitats and their biota.

Animal Migration↗

Analysis of microsatellite variation in Pinus radiata reveals effects of genetic drift but no recent bottlenecks.

Most conifer species occur in large continuous populations, but radiata pine, Pinus radiata, occurs only in five disjunctive natural populations in California and Mexico. The Mexican island populations were presumably colonized from the mainland millions of years ago. According to Axelrod (1981), the mainland populations are relicts of an earlier much wider distribution, reduced some 8,000 years ago, whereas according to Millar (1997, 2000), the patchy metapopulation-like structure is typical of the long-term population demography of the species. We used 19 highly polymorphic microsatellite loci to describe population structure and to search for signs of the dynamics of population demography over space and time. Frequencies of null alleles at microsatellite loci were estimated using an approach based on the probability of identity by descent. Microsatellite genetic diversities were high in all populations [expected heterozygosity (H(e)) = 0.68-0.77], but the island populations had significantly lower estimates. Variation between loci in genetic differentiation (F(ST)) was high, but no locus deviated statistically significantly from the rest at an experiment wide level of 0.05. Thus, all loci were included in subsequent analysis. The average differentiation was measured as F(ST) = 0.14 (SD 0.012), comparable with earlier allozyme results. The island populations were more diverged from the other populations and from an inferred common ancestral gene pool than the mainland ones. All populations showed a deficiency of expected heterozygosity given the number of alleles, the mainland populations more so than the island ones. The results thus do not support a recent important contraction in the mainland range of radiata pine.

California↗

Peptic esophageal stricture: a report from Argentina.

Peptic esophageal stricture (PES) is a major complication of gastroesophageal reflux disease. The aims of this paper were to determine the characteristics of these patients with regard to demography, morphology, functional status and results of therapy. The charts of the patients treated at our service who underwent esophageal dilatation for PES between 1971 and 1998 were reviewed. Statistical analyses were performed by means of chi2, Mann-Whitney and Student's t-tests. One hundred and thirty-five patients with PES were dilated by various means. The mean age was 61.1 +/- 16.3 years, the ratio of men to women was 2.75/1 and mean duration of symptoms was 44.4 +/- 74.6 months. Their symptoms were dysphagia in 100%, pyrosis in 70%, and regurgitation in 40% of the cases. There was an average weight loss of 3.3 +/- 6 kg. The upper gastro-intestinal series showed pre- and post-dilatation diameters at the stricture of 8 +/- 2.5 mm and 15.9 +/- 1.2 mm, respectively. The stricture was located at the lower third of the esophagus in 97% and at the middle third in 3% of the cases. We found PES endoscopically in all instances, with different degrees of erosions in 64%, ulcers in 20% and Barrett's esophagus in 16% of the cases. The biopsy samples showed intestinal metaplasia in 16% and esophagitis in 75.5%, being normal in the remaining 8.5%. Brush cytology was negative for malignancy in 100% of the cases. Esophageal manometry showed peristaltic wave amplitude of 40 +/- 3 mmHg and presence of peristaltic waves of 62 +/- 38.6%. LES pressure was 8.6 +/- 6.3 mmHg (NV 24.2 +/- 6.3 mmHg). Measurement of pH showed 15% of patients had pH < 4. Patients needed a mean of 4.7 +/- 1.6 dilations per case, with successful results in 87.2% of cases. The perforation rate was 0.1% of the total number of procedures and 0.7%, of patients. The mortality rate was 0.7% (one case). We observed PES relapse in 32% of the cases. There was no correlation between relapse, age, duration of the stenosis or pharmacological treatment with H2 blockers or proton pump inhibitors. We conclude that in Argentina, demography, morphology, functional status and results of dilatation of PES patients are similar to those reported in the Western world, with the exception of the different behavior seen after treatment with H2 blockers or proton pump inhibitors.

Adult↗

Conservation of species in dynamic landscapes: divergent fates of Silene tatarica populations in riparian habitats.

In transient environments, where local extinctions occur as a result of destruction or deterioration of the local habitat, the long-term persistence of a species requires successful colonizations at new, suitable sites. This kind of habitat tracking should be associated with the asynchronous dynamics of local populations, and it can be especially important for the conservation of rare plant species in riparian habitats. We determined spatiotemporal variation in the demography of the perennial Silene tatarica (L.) Pers. in 15 populations (1998-2003) located in periodically disturbed riparian habitats. The habitats differed according to their morphology (flat shores, slopes) and the amount of bare ground (open, intermediate, closed) along a successional gradient. We used elasticity and life-table response analyses and stochastic simulations to study the variation in population demography. Finite population growth rate was higher in intermediate habitats than in open and closed habitats. In stochastic simulations population size increased in most cases, but four populations were projected to become extinct within 12-70 years. The viability of local populations depended most on the survival and growth of juvenile individuals and on the fecundity of large fertile individuals. On a regional scale, the persistence of this species will require a viable network of local populations as protection against local extinctions caused by natural disturbances and succession. Accordingly, the long-term persistence of riparian species may depend on habitat changes; thus, their conservation requires maintenance of natural disturbance dynamics. Along regulated rivers, management activities such as the creation of open habitats for new colonization should be implemented. Similarly, these activities can be rather general requirements for the conservation of endangered species dependent on transient habitats along successional gradients.

Computer Simulation↗

Demographic characteristics and population dynamical patterns of solitary birds.

In birds and many other animals, there are large interspecific differences in the magnitude of annual variation in population size. Using time-series data on populations of solitary bird species, we found that fluctuations in population size of solitary birds were affected by the deterministic characteristics of the population dynamics as well as the stochastic factors. In species with highly variable populations, annual variation in recruitment was positively related to the return rate of adults between successive breeding seasons. In stable populations, more recruits were found in years with low return rates of breeding adults. This identifies a gradient, associated with the position of the species along a "slow-fast" continuum of life history variation, from highly variable populations with a recruitment-driven demography to stable, strongly density-regulated populations with a survival-restricted demography. These results suggest that patterns in avian population fluctuations can be predicted from a knowledge of life-history characteristics and/or temporal variation in certain demographic traits.

Animals↗