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PubMed2006

Dispersal per recruit: an efficient method for assessing sustainability in marine reserve networks.

Marine reserves are an increasingly important tool for the management of marine ecosystems around the world. However, the effects of proposed marine reserve configurations on sustainability and yield of populations are typically not estimated because of the computational intensity of direct simulation and uncertainty in larval dispersal and density-dependent recruitment. Here we develop a method for efficiently assessing a marine reserve configuration for persistence and yield of a population with sedentary adults and dispersing larvae. The method extends the familiar sustainability criteria of individual replacement for single populations based on eggs-per-recruit (EPR) to spatially distributed populations with sedentary adults, a dispersing larval phase, and limited carrying capacity in the settlement-recruit relationship. We refer to this approach as dispersal-per-recruit (DPR). In some cases, a single DPR calculation, based on the assumption that post-settlement habitat is saturated (i.e., at maximum recruitment), is sufficient to determine population persistence, while in other cases further iterative calculations are required. These additional calculations reach an equilibrium more rapidly than a full simulation of age- or size-structured populations. From the DPR result, fishery yield can be computed from yield-per-recruit (YPR) at each point. We assess the utility of DPR calculations by applying them to single reserves, uniformly distributed systems of reserves, and randomly sized and spaced systems of reserves on a linear coastline. We find that for low levels of EPR in fished areas (e.g., 10% or less of the natural, unfished EPR when post-settlement habitats are saturated by 35% of natural settlement), a single DPR calculation is sufficient to determine persistence of the population. We also show that, in uniform systems of reserves with finite reserve size, maximal fisheries yield occurs when the density of reserves is such that all post-settlement habitat is nearly saturated with settlers. Finally, we demonstrate the application of this approach to a realistic proposed marine reserve configuration.

Animals↗

PubMed1986

[Quebec's population decline: if it is foreseeable, is it avoidable?].

"Quebec's fertility is the lowest in Canada, and it is most likely that its population is heading for a decline. In this paper, the authors try to make explicit some of the scenarios which could prevent this decline. They first briefly present the current trends and specify the assumptions used in the simulation. Then, they analyse the results by investigating the onset of the decline and the maximum size of the population. And finally, they present some of the replacement scenarios which may prevent the decline." (SUMMARY IN ENG AND SPA)

Americas↗

PubMed2004

Population genetics of autocidal control and strain replacement.

The concept that an insect species' genome could be altered in a manner that would result in the control of that species (i.e., autocidal control) or in the replacement of a pestiferous strain of the species with a more benign genotype was first proposed in the mid-twentieth century. A major research effort in population genetics and ecology followed and led to the development of a set of classical genetic control approaches that included use of sterile males, conditional lethal genes, translocations, compound chromosomes, and microbe-mediated infertility. Although there have been a number of major successes in application of classical genetic control, research in this area has declined in the past 20 years for technical and societal reasons. Recent advances in molecular biology and transgenesis research have renewed interest in genetically based control methods because these advances may remove some major technical problems that have constrained effective genetic manipulation of pest species. Population genetic analyses suggest that transgenic manipulations may enable development of strains that would be 10 to over 100 times more efficient than strains developed by classical methods. Some of the proposed molecular approaches to genetic control involve modifications of classical approaches such as conditional lethality, whereas others are novel. Experience from the classical era of genetic control research indicates that the population structure and population dynamics of the target population will determine which, if any, genetic control approaches would be appropriate for addressing a specific problem. As such, there continues to be a need for ongoing communication between scientists who are developing strains and those who study the native pest populations.

Animals↗

PubMedDate not supplied

[The effect of the alkylating carcinogen dipin on the proliferation, the level of polyploidy development and on micronucleus formation in a population of parent and newly formed hepatocytes].

In the process of hepatocarcinogenesis induced by dipin and partial hepatectomy in mice, initial hepatocytes are gradually replaced with a population of newly formed hepatocytes which originate from oval cells (Radaeva, Factor, 1990). It has been shown that the increase in hepatocarcinogenesis duration (2-11 weeks) along with the intensification of oval-cell reaction are accompanied by a progressive injury of cell genome in the initial hepatocyte population. This injury manifests itself by an accumulation of cells with micronuclei as well as by the development of high levels of polyploidy and aneuploidy. In the initial parenchyma, clastogenic and aneuploidizing effects of dipin are maximally pronounced at the stage of appearing hepatocyte nodules which consist of newly formed hepatocytes (8-11 weeks). By this time the proliferative pool comprises 83-92%, the amount of aberrant cells increases in average from 7 to 50%, and the indices of average nuclear ploidy in population enhance 6-8 times as compared with the average level of polyploidy in normal parenchyma. The quota of binuclear cells without micronuclei abruptly falls while the quota of binuclear cells with micronuclei and nuclear bridges increases reaching 3/4 of the total amount of binuclear cells. Binuclear cells with nuclear bridges comprise about one third of binuclear cells with micronuclei. At the stage of hepatocytic nodules (8-11 weeks after induction), the population of newly formed hepatocytes is characterized by the absence of morphologically damaged cells and of cells with micronuclei, a low incidence of binuclear cells (1-3%), and a high value of proliferative pool (83-96%).

Alkylating Agents↗

PubMed1989

One selectionist's perspective.

Following introductory comments expressing doubts about the validity of genetic load and Haldane's "cost of natural selection," the role of selection (expressed as the average number of adult daughters per female) on gene frequencies in populations has been partitioned into population and time arenas. The population arena (a geometric plane) deals with the fitnesses of different genotypes under the many situations encountered by individual members of the population in a single generation; average fitnesses of carriers of various genotypes are obtained by calculating across these many situations. The population arena includes the point signifying that, on the average, each mother leaves one daughter as her replacement within the population. It is the plane within which evolutionarily significant norms of reaction exist. The time arena is also a (geometric) plane, one that is composed of the edge-on limit (average fitness) of each successive population arena. It does not include the effects of individual situations on relative fitnesses within each population arena; it encompasses only the temporal sequence of average relative fitnesses. Amino acid substitutions in proteins and base-pair substitutions in DNA are events of concern in the time arena; within the population arena, however, gene action (not merely gene structure) is a matter of considerable concern. Thus, the discussions of the 1950s and 1960s regarding genetic variation which were reasonable within the population arena seem less so within the time arena where structural, rather than functional, variation is stressed. The function-structure dichotomy is entangled with the neutralist-selectionist controversy.

Alleles↗

PubMed2006

Effects of testosterone replacement in androgen-deficient women with hypopituitarism: a randomized, double-blind, placebo-controlled study.

CONTEXT: Hypopituitarism in women is characterized by profound androgen deficiency due to a loss of adrenal and/or ovarian function. The effects of testosterone replacement in this population have not been reported. OBJECTIVE: The objective of the study was to determine whether physiologic testosterone replacement improves bone density, body composition, and/or neurobehavioral function in women with severe androgen deficiency secondary to hypopituitarism. DESIGN: This was a 12-month randomized, placebo-controlled study. SETTING: The study was conducted at a general clinical research center. STUDY PARTICIPANTS: Fifty-one women of reproductive age with androgen deficiency due to hypopituitarism participated. INTERVENTION: Physiologic testosterone administration using a patch that delivers 300 microg daily or placebo was administered. MAIN OUTCOME MEASURES: Bone density, fat-free mass, and fat mass were measured by dual x-ray absorptiometry. Thigh muscle and abdominal cross-sectional area were measured by computed tomography scan. Mood, sexual function, quality of life, and cognitive function were assessed using self-administered questionnaires. RESULTS: Mean free testosterone increased into the normal range during testosterone administration. Mean hip (P = 0.023) and radius (P = 0.007), but not posteroanterior spine, bone mineral density increased in the group receiving testosterone, compared with placebo, as did mean fat-free mass (P = 0.040) and thigh muscle area (P = 0.038), but there was no change in fat mass. Mood (P = 0.029) and sexual function (P = 0.044) improved, as did some aspects of quality of life, but not cognitive function. Testosterone at physiologic replacement levels was well tolerated, with few side effects. CONCLUSIONS: This is the first randomized, double-blind, placebo-controlled study to show a positive effect of testosterone on bone density, body composition, and neurobehavioral function in women with severe androgen deficiency due to hypopituitarism.

Adrenal Insufficiency↗

PubMed1995

Medtronic Intact porcine bioprosthesis: clinical performance to seven years.

The clinical performance of the Medtronic Intact porcine bioprosthesis was evaluated in 1,084 patients (mean age 66.4 years, range 9 to 91 years) who had a total of 1,099 implantations between 1985 and 1992, inclusive. There were 709 aortic valve replacements, 297 mitral valve replacements, and 80 multiple valve replacements. Concomitant procedures were performed in 432 (39.3%). The age group distribution (years) was 35 or younger in 20 patients, 36 to 50 in 64, 51 to 64 in 274, 65 to 69 in 225, 70 or older in 500. The total follow-up time was 2,741 patient-years (mean, 2.5 years) and was 97.5% complete. The early mortality rate was 7.1% and late mortality was 3.9% per patient-year. The overall patient survival at 7 years was 70% +/- 3%. The freedom from major thromboembolism was 94% +/- 1% at 7 years (p = not significant for valve positions). The freedom from reoperation at 7 years was 93% +/- 1%; freedom from valve-related mortality was 89% +/- 2%. The freedom from structural valve deterioration at 7 years was 97% +/- 1% (aortic valve replacement 97% +/- 1%; mitral valve replacement 97% +/- 2%). The freedom from structural valve deterioration among age groups was not different for the overall population, aortic valve replacement, or mitral valve replacement. Hemodynamic assessment revealed obstructive properties for aortic valve replacement sizes of 21 and 23 mm and for mitral valve replacement sizes of 25 and 27 mm.(ABSTRACT TRUNCATED AT 250 WORDS)

Actuarial Analysis↗

PubMed2004

Total hip arthroplasty in patients 50 years and younger.

Because the young patient with a total hip arthroplasty is presumed to place increased demands on a reconstruction for a longer period than the average patient with a hip replacement, long-term results are expected to be inferior. To determine the efficacy of total hip replacements in this population, the current authors reviewed the long-term results of patients who were 50 years and younger who had cementless total hip arthroplasties at their institution, and reviewed the literature on total hip arthroplasty in younger patients. The results from the study population and the literature were encouraging. At the author's institute, during the past 20 years, 561 hip replacements were done on 488 patients in this age group, using extensively porous-coated cobalt-chromium stems matched with beaded, press-fit acetabular components of cobalt-chrome or titanium. Using the Kaplan-Meier technique, the survival rates for femoral and acetabular components, using any revision as an end point, were 89% at 10-year followup and 60% at 15-year followup. A subset of the authors' patients who were 40 years and younger (256 hips, 223 patients) had slightly inferior results, with 85% 10-year survivorship and 54% 15-year survivorship, using any revision as an end point. A comprehensive literature review also showed that long-term success can be achieved with cemented or cementless total hip arthroplasties in young patients. Because some reconstructions exhibited inferior results in younger patients, the authors recommend that surgeons be much more critical of the components used in these patients and allow long-term data to guide their decisions.

Adolescent↗

PubMed2005

Mitral valve replacement with and without chordal preservation in a rheumatic population: serial echocardiographic assessment of left ventricular size and function.

BACKGROUND: The aim of this study is to investigate the feasibility of chordal-sparing mitral valve replacement procedures in a rheumatic population, and to determine the early and late effects of different chordal preservation procedures on the clinical outcome and left ventricular mechanics. METHODS: Various techniques of chordal preservation during mitral valve replacement for rheumatic heart disease in 451 patients between 1996 and 1999 are described. The mean age was 35.6 +/- 19.0 years (range, 15 to 55 years). Seventy patients had complete excision of the subvalvular apparatus (group I), 124 had preservation of the posterior chordopapillary apparatus (group II), and 257 had total chordal preservation (group III). Echocardiography was performed preoperatively, at discharge, at 1 year, and at 4 years. RESULTS: Chordal preservation groups (II and III) demonstrated significant improvement (p < 0.05) in left ventricular function immediately and late postoperatively. Reduction of left ventricular end-systolic and end-diastolic volume was significant in the chordal preservation groups (II and III) as compared to the nonchordal group (group I; p < 0.005). The total chordal group demonstrated greater fractional change of left ventricular end-systolic volume as compared to the posterior chordal and nonchordal group. The left ventricular ejection fraction and fractional shortening continued to decline over time in the nonchordal cohort (p = 0.05 and p = 0.001, respectively) and did not improve by 4 years. Statistically significant change in ejection fraction occurred in the chordal preservation groups as compared to the nonchordal group. CONCLUSIONS: We conclude that total chordal preservation is possible in the large majority of rheumatic patients and confers significant long-term advantage by preserving left ventricular function. The surgical technique should be individualized.

Adult↗

PubMed2003

Influence of hormone replacement therapy on C-reactive protein: population-based data.

BACKGROUND: Observational data, possibly resulting from confounding due to self-selection, show that use of hormone replacement therapy (HRT) is associated with reduced coronary risk, while randomized trial data do not. One possible explanation for the trial findings is that adverse effects of HRT-- such as an elevation of C-reactive protein (CRP)--might counterbalance other benefits of HRT. DESIGN: Women aged 40-74 years were identified from a cross-sectional, annual nationally representative study of the English population, the Health Survey for England 1998. Valid data were available from 4,112 of the 4,319 women in this age group. Of these, 710 (17%) were current, 465 (11%) past and 2,937 (71%) never users of HRT. METHODS: To study the association between current and past use of HRT and CRP levels. CRP was expressed as a continuous variable (logged) and in percentiles. RESULTS: Current, past and never users of HRT did not differ in terms of age, body mass index or smoking status. However, compared with past and never users of HRT, current users tended to take more vigorous physical activity and were more likely to drink more alcohol than is currently recommended. Excluding potentially confounding conditions, median CRP levels were significantly higher in current (2.5 mg/l) and in past (1.9 mg/l) than never HRT users (1.4 mg/l). Controlling for age, smoking and body mass index logged CRP remained significantly raised only among current users. CONCLUSIONS: HRT use was significantly and independently associated with raised CRP levels in an English nationally representative sample. Increases in CRP may represent one plausible mechanism by which HRT may adversely affect risk of coronary heart disease.

Adult↗

PubMed1988

Condition of prosthetic constructions and subjective needs for replacing missing teeth in a Finnish adult population.

Prosthetic treatment needs were studied in a sample of 1600 adults distributed equally into cohorts aged 25, 35, 50 and 65 years. A total of 1275 subjects (80%) were clinically examined with respect to the condition and age of existing prosthetic constructions, subjective needs for replacing missing teeth and the frequency of oral mucosal lesions associated with the wearing of dentures. Approximately half of the removable dentures (56%) were objectively non-acceptable and one-third (36%) subjectively so. One in four of those subjects with missing anterior teeth and premolars, or with 0-2 remaining mandibular molars and one in five of those with 0-2 remaining maxillary molars expressed a need to have one or more of the missing teeth replaced. The replacement needs were slightly greater for missing anterior teeth and premolars than for molars. Subjective needs for replacing missing teeth were greatest at the age of 50 years. The condition of removable dentures according to objective assessment was poorest among those aged 65 years. A high frequency of mucosal lesions associated with old and non-acceptable removable dentures was observed.

Adult↗

PubMed1999

Hormone replacement therapy and screening mammography: analysis of the results in the Bouches du Rhône programme.

OBJECTIVE: To evaluate the effectiveness of a mass screening programme for breast cancer in a French population where hormone replacement therapy (HRT) is common and where mammography is prescribed outside the programme for asymptomatic women. METHODS: From 1993 to 1996 inclusive, 41,062 women underwent a first test and 48,275 a second or third test in the Bouches du Rhône programme. Their HRT status was ascertained at the time of the test. False positive and false negative tests were identified at one year follow up. The incidence of interval cancers was estimated up to three years after the screening test. RESULTS: The odds of being detected at screening rather than as an interval cancer within one year of the test was five times greater among non-users of HRT than among users (odds ratio (OR) 5.14 (confidence interval 2.5 to 11.8)). This high reduction in sensitivity among users (71% v 92%) was associated with a very small reduction in specificity at the incident screen only. The incidence of interval cancers among HRT users was 3.5 times that of non-users within the first year after the test and 1.7 times during the following two years. CONCLUSIONS: When the early results of a programme have been used to measure its effectiveness they should be reassessed in populations where HRT is in widespread use. As interval cancers had better prognostic factors in HRT users than in non-users, the efficacy of a screening programme in such populations should be the subject of further studies.

Aged↗

PubMed2003

Receipt of renal replacement therapy in the United States: a population-based study of sociodemographic disparities from the Second National Health and Nutrition Examination Survey (NHANES II).

BACKGROUND: Persons with chronic kidney disease who need kidney replacement therapy to sustain life have health insurance. We examined whether young adults, women, blacks, less-educated persons, the poor, and persons residing in less populated areas receive treatment when health insurance is no longer a barrier. METHODS: We conducted a case-control study nested in the Second National Health and Nutrition Examination Survey Mortality Study. Cases were persons treated with kidney replacement therapy determined by linkage to the end-stage renal disease treatment registry. Controls were untreated persons with kidney disease who died not appearing in the registry. RESULTS: During 12 to 16 years, 44 persons developed treated disease, and 145 persons, untreated disease. After adjustment for sex, age, education, population of residential area, and comorbid conditions in logistic regression analysis, younger versus older age and living in a highly populated versus less populated area were both independently associated with treatment (relative odds of treatment, 5.57; 95% confidence interval, 1.72 to 18.0; and 4.33; 95% confidence interval, 2.09 to 8.97, respectively). Race, sex, education, and poverty were not associated with less treatment. CONCLUSION: We found no disparity in life-saving chronic kidney disease treatment with regard to race or socioeconomic status in this population-based study. Less receipt of treatment by older adults may reflect greater comorbid disease or choices made by persons or their providers. Strategies to render treatment in less populated areas, including incentives to deliver care to such areas, should be encouraged.

Adult↗

PubMed1999

The oldest patient to undergo aortic valve replacement.

As the American population ages, more elderly patients will present with significant heart disease. This group has an increase in morbidity and mortality with heart surgery as compared to a younger population. Severe aortic stenosis has a grave prognosis, and therefore surgical options should be considered even in the most elderly patient with this condition. We present the oldest reported patient to undergo aortic valve replacement for severe aortic stenosis.

Age Factors↗

PubMed2002

Large-scale pathology-based cancer data--a reflection of population-based cancer data.

Pathology-based cancer data is a high quality reflection of the patterns of cancer in the population it represents, provided the demographic details of the patients are carefully recorded. Relative frequency data is neither a replacement for population-based data nor a suggested alternative; it simply enhances the quality of population data and in very large data sets reflects the cancer patterns observed in the representative populations. Aware of the standard shortfalls of pathology-based data, the department of pathology, The Aga Khan University Hospital (AKUH) standardized its data, representing 53.4% of the cancer data of Karachi Division (Pakistan) and also reflecting the cancer pattern of other provinces of Pakistan. This data was compared with 4 different population and institutional-based data sets. The findings substantiate the observation that despite the problems of interpretation of data from pathology laboratories, they are an invaluable source of information on cancer patterns in much of the world where incidence data are unavailable . If developing countries, unable to organize National Population- Based Registry should as an alternate develop National Pathology-based Registers a well targeted and monitored, a Cancer Control Program would be possible. A good quality, large-scale pathology data with demographic details of the patient recorded can also be extended to give coverage to the population.

Female↗

PubMed2006

Population-scale assessment endpoints in ecological risk assessment. Part 1: Reflections of stakeholder values.

The selection of appropriate assessment endpoints is a basic element of an ecological risk assessment, especially at regional or watershed scales. Because ecological services often are tied to specific species, the risk to populations is a critical endpoint and feature of ecological risk assessments. The first item is a discussion of the replacement of population-level risk assessment with the construct of a population-scale assessment endpoint. Next, the criteria that are currently used for assessment endpoints are reviewed and evaluated for utility in an ecological risk assessment. Following this examination, assessment endpoints from a number of regional-scale ecological risk assessments are compared. The outcome of this evaluation is that population-scale assessment endpoints are important expressions of the valued components of ecological structures. Finally, a few recommendations for the selection of assessment endpoints at a population scale are listed.

Animals↗

PubMed2005

Transgenic mosquitoes and malaria transmission.

As the malaria burden persists in most parts of the developing world, the concept of implementation of new strategies such as the use of genetically modified mosquitoes to control the disease continues to gain support. In Africa, which suffers most from malaria, mosquito vector populations are spread almost throughout the entire continent, and the parasite reservoir is big and continuously increasing. Moreover, malaria is transmitted by many species of anophelines with specific seasonal and geographical patterns. Therefore, a well designed, evolutionarily robust and publicly accepted plan aiming at population reduction or replacement is required. The task is twofold: to engineer mosquitoes with a genetic trait that confers resistance to malaria or causes population suppression; and, to drive the new trait through field populations. This review examines these two issues, and describes the groundwork that has been done towards understanding of the complex relation between the parasite and its vector.

Africa↗

PubMed2005

Transposable elements in mosquitoes.

We describe the current state of knowledge about transposable elements (TEs) in different mosquito species. DNA-based elements (class II elements), non-LTR retrotransposons (class I elements), and MITEs (Miniature Inverted Repeat Transposable Elements) are found in the three genera, Anopheles, Aedes and Culex, whereas LTR retrotransposons (class I elements) are found only in Anopheles and Aedes. Mosquitoes were the first insects in which MITEs were reported; they have several LTR retrotransposons belonging to the Pao family, which is distinct from the Gypsy-Ty3 and Copia-Ty1 families. The number of TE copies shows huge variations between classes of TEs within a given species (from 1 to 1000), in sharp contrast to Drosophila, which shows only relatively minor differences in copy number between elements (from 1 to 100). The genomes of these insects therefore display major differences in the amount of TEs and therefore in their structure and global composition. We emphasize the need for more population genetic data about the activity of TEs, their distribution over chromosomes and their frequencies in natural populations of mosquitoes, to further the current attempts to develop a transgenic mosquito unable to transmit malaria that is intended to replace the natural populations.

Animals↗