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PubMed1999

A theoretical basis for measuring the efficiency of selection in plant breeding

A new index of selection efficiency, i.e. the ratio of the probability of achieving the desired genetic gain in a target population to the cost expended for that gain, is introduced to define the optimum selection procedures that give the most opportunities for producing new commercial varieties. Monte Carlo simulations of mass selection showed that the index gives solutions to some important optimization problems which cannot be solved based on the traditional indices, the expected genetic gain or its ratio to the cost. The optimum cycle and intensity of selection and optimum population size for a target population could be defined by the new index, but not by the traditional indices.

Journal Article↗
PubMed1996

The epidemiology of obesity.

An agreed definition of obesity as a body mass index (BMI) of 30 kg/m2 or more seems to be accepted everywhere except in North America. Recent data confirm the importance of setting an upper individual BMI limit of 25 kg/m2 and a population optimum of 20-23 kg/m2. Some adjustment of BMI should be made in individuals and populations with disproportionate shapes, e.g. short or long legs, and morbidity and mortality risks are especially important in those with a waist measurement of about 102 cm or more, the risk increasing from 88 cm. Waist measurements should probably now be substituted for the waist/hip circumference ratio. Diabetes is universally closely linked to increases in BMI, and cardiovascular disease is amplified by obesity, particularly in western societies where other dietary factors contribute substantially. Industrialization with reduced physical activity and higher fat diets lead to obesity first in middle-aged women, then in men, with younger adults and children eventually being affected. Physiological studies display the interaction of physical activity and energy dense, high fat diets and explain the secular, age- and social class-related trends throughout the world. Intergenerational amplification of obesity may be underway, so the public health implications of obesity are immense.

Adult↗
PubMed2006

Optimized growth kinetics of Pichia pastoris and recombinant Candida rugosa LIP1 production by RSM.

A predictive model for Pichia pastoris expression of highly active recombinant Candida rugosa LIP1 was developed by combining the Gompertz function and response surface methodology (RSM) to evaluate the effect of yeast extract concentration, glucose concentration, temperature, and pH on specific responses. Each of the responses (maximum population densities, specific growth rate (mumax), protein concentration, and minimum lag phase duration) was determined using the modified Gompertz function. RSM and 4-factor-5-level central composite rotatable design (CCRD) were adopted to evaluate the effects of growth parameters, such as temperature (21.6-38.4 degrees C), glucose concentration (0.3-3.7%), yeast extract (0.16-1.84%), and pH (5.3-8.7) on the responses of P. pastoris growth kinetics. Based on ridge maximum analysis, the optimum population density conditions were: temperature 24.4 degrees C, glucose concentration 2.0%, yeast extract 1.5%, and pH 7.6. The optimum specific growth rate conditions were: temperature 28.9 degrees C, glucose concentration 2.0%, yeast extract 1.1%, and pH 6.9. The optimum protein concentration conditions were: temperature 24.2 degrees C, glucose concentration 1.9%, yeast extract 1.5%, and pH 7.6. Based on ridge minimum analysis, the minimal lag phase conditions were: temperature 32.3 degrees C, glucose concentration 2.1%, yeast extract 1.1%, and pH 5.4. For the predicted value, the maximum population density, specific growth rate, protein concentration, and minimum lag phase duration were 15.7 mg/ml, 3.4 h(-1), 0.78 mg/ml, and 4.2 h, and the actual values were 14.3 +/- 3.5 mg/ml, 3.6 +/- 0.6 h(-1), 0.72 +/- 0.2 mg/ml, and 4.4 +/- 1.6 h, respectively.

Candida↗
PubMed2001

Buffer zones promoting oligotrophication in golf course runoffs: fiddler crabs as estuarine health indicators.

Nitrogen pollution above a threshold level induces a eutrophication process in coastal creek ecosystems and consequently impacts on the water quality. The remedy for this scenario is the introduction of methods to enhance oligotrophication by means of constructed wetlands and buffer zones. This paper discusses new data on nitrogen flux and population changes in the primary consumers in the Bradley Creek ecosystem, adjacent to the Duck Haven Golf Course in southeastern North Carolina. In 1998-99, over different seasons, density distribution of the field populations of the fiddler crab Uca minax, was monitored as an indicator of environmental health. A control site at Whiskey Creek, adjacent to the University Center for Marine Sciences, was monitored in the same period since this site is not influenced by any golf course nutrient flux. The results pointed out that threshold level for optimum population density in Spartina grandiflora salt marsh is 0.1 mg/L of nitrates. A dense crab population, adjacent to the golf course with a buffer zone, was indicative of restoration of the estuarine ecosystem. A model, involving the use of constructed wetlands for oligotrophication, is being prepared on the basis of studies conducted by the University of South Alabama for a stormwater wetland constructed adjacent to the university's golf course.

Animals↗
PubMed2002

Estimating carrying capacity in a newly colonized sand fly Lutzomyia serrana (Diptera: Psychodidae).

The phlebotomine sand fly Lutzomyia serrana (Damasceno & Arouck) was mass-reared tinder conditions of varying densities in an effort to improve colony production efficiency. To do this, the experimental carrying capacity of a standard rearing chamber was determined, i.e., the optimum population size in relation to density (individuals per unit of space). Rearing chambers of 100 cm3 were populated with 1-50 L. serrana engorged females and an equal number of males. Laboratory conditions were maintained at 23-26 degrees C and 85-95% RH. The following parameters were recorded for each experimental chamber (three replicates): (1) female mortality without oviposition, (2) number of eggs oviposited and (3) number of adults emerging from the egg cohort. Female mortality began to increase substantially in the 26-female chamber, from 5.7% to 15% and finally reaching 60.2% in the 46-50 female chambers. In the chambers containing 1-20 females, egg number and realized adult progeny increased linearly to reach an asymptote. In the 20-50 female chambers, the number of eggs ranged from 420 to 699, and adult production from 306 to 432. The optimum carrying capacity for the 100-cm3 chambers was 22 +/- 2 females. Beyond this number, auto-regulation was initiated, i.e., female mortality without oviposition increased as the number of females per chamber increased. Total number of eggs and adult production was similar in all chambers containing 20-50 females. In conclusion, for optimizing production of mass reared sand flies, determination of the carrying capacity is essential to optimize use of insectary resources, to avoid loss of valuable potentially ovipositing females, and to increase overall production efficiency.

Animals↗
PubMed2005

Two-generation marker-aided backcrossing for rapid conversion of normal maize lines to quality protein maize (QPM).

The low nutritive value of maize endosperm protein is genetically corrected in quality protein maize (QPM), which contains the opaque 2 gene along with numerous modifiers for kernel hardness. We report here a two generation marker-based backcross breeding program for incorporation of the opaque 2 gene along with phenotypic selection for kernel modification in the background of an early maturing normal maize inbred line, V25. Using the flanking marker distances from opaque 2 gene in the cross V 25 xCML 176, optimum population size for the BC(2) generation was computed in such a way that at least one double recombinant could be obtained. Whole genome background selection in the BC(2) generation identified three plants with 93 to 96% recurrent parent genome content. The three BC(2)F(2) families derived from marker identified BC(2) individuals were subjected to foreground selection and phenotypic selection for kernel modification. The tryptophan concentration in endosperm protein was significantly enhanced in all the three classes of kernel modification viz., less than 25%, 25--50% and more than 50% opaqueness. BC(2)F(3) lines developed from the hard endosperm kernels were evaluated for desirable agronomic and biochemical traits in replicated trials and the best line was chosen to represent the QPM version of V25, with tryptophan concentration of 0.85% in protein. The integrated breeding strategy reported here can be applied to reduce genetic drag as well as the time involved in a conventional line conversion program, and would prove valuable in rapid development of specialty corn germ plasm.

Crosses, Genetic↗
PubMed2006

Current understanding of optimal blood pressure goals in dialysis patients.

The hemodialysis population is associated with a very low survival rate, with myocardial infarctions and strokes accounting for most of the increased mortality. Recent observational studies demonstrate a paradoxical relationship between increasing blood pressure and increasing mortality. Hypertension treated with antihypertensive medications unequivocally reduces cerebrovascular risk, but demonstration of a survival benefit for cardiovascular mortality has proven more difficult to demonstrate. Increased pulse pressure is caused by inadequate dialysis treatment that increases arterial wall stiffness and afterload, and decreases coronary perfusion. The disproportionate representation of diastolic dysfunction and coronary artery atherosclerosis may explain why increased pulse pressure is associated with higher cardiovascular risk for the dialysis population. Optimum blood pressure control has not been established, due to a lack of prospective studies targeting blood pressure reduction. Opinion-based recommendations are offered, but goals should be individualized based on a complete assessment of prevailing comorbidities and should target normalization of the pulse pressure.

Antihypertensive Agents↗
PubMed1998

Where should paediatric surgery be performed?

We have tried to review the evidence for the organisation of paediatric surgical care. Difficulties arise because of the lack of published data from district general hospitals concerning paediatric surgical conditions. Hence much of the debate about the surgical management of children is based on anecdotal evidence. However, at a time when the provision of health care is being radically reorganised to an internal market based on a system of purchasers and providers it is more important than ever to understand the issues at stake. Two separate issues have been discussed: the role of the specialist paediatric centre and the provision of non-specialist paediatric surgery in district general hospitals. There are arguments for and against large regional specialist paediatric centres. The benefits of centralisation include concentration of expertise, more appropriate consultant on call commitment, development of support services, and junior doctor training. The disadvantages include children and their families having to travel long distances for care, and the loss of expertise at a local level. If specialist paediatric emergency transport is available the benefits of centralisation far outweigh the adverse effects of having to take children to a regional paediatric intensive care centre. Specialist paediatric centres are aware of the importance of treating children and their parents as a family unit as highlighted by the Platt committee; this is an important challenge and enormous improvements have occurred to provide proper accommodation for families while their children are treated in hospital. To keep these arguments of large distances and separation from the home in context, one paediatric intensive care unit in Victoria, Australia, providing a centralised service to a region larger in are than England and with a similar admission rate, has a lower mortality rate than the decentralised paediatric intensive care provided in the Trent region of the UK. There is clear evidence that all neonatal surgery and anaesthesia should be conducted only by specialists. The debate now centres around the number of complex surgical cases a unit should treat to maintain its specialist status. The NHS executive, in its guidelines on contracting for specialist services, emphasises that "Sensible contracting needs to take into account the optimum population size not only for the stability of contracted referrals but also to give sufficient 'critical mass' for clinical effectiveness." Achieving this balance has consequences, not just for the maintenance of surgical expertise, but for the essential ancilliary services. There is clear evidence in anaesthesia that anaesthetists doing small numbers of neonatal procedures had significantly worse results. The same seems to be true in the fields of oncology, radiology, pathology, and intensive care. The reasons why the results of management of certain paediatric conditions are better at specialist centres are open to speculation. Presumably greater exposure to rare complex cases, concentration of expertise, more peer review, and a trickle down effect of the multidisciplinary approach all help to keep health care workers up to date with current world practice. In addition, it allows for appropriate specialist on call rotas and dedicated junior staff. If insufficient numbers of specialist surgical cases are being treated at a centre then the whole multidisciplinary team suffers. The 1989 NCEPOD report states "that paediatricians and general surgeons must recognise that small babies differ from other patients not only in size, and that they pose quite separate problems of pathology and management." The need for large centres of paediatric surgical expertise is now accepted by the Royal College of Surgeons of England, the British Association of Paediatric Surgeons, the Senate of Surgery of Great Britain and Ireland, the Royal College of Paediatrics and Child Health, the Royal College of Anaesthetists, the Audit

Anesthesiology↗
PubMed1982

Optimizing the dental delivery system.

This paper examines the application of information and principles derived from social science research to increasing the effectiveness and efficiency of the dental care delivery system. Four major delivery system attributes are considered: the availability, accessibility, appropriateness and acceptability of care. The dentist to population ratio is a major determinant of the availability of dental care and many factors have to be considered in deciding on the appropriate number of dentists needed in a population. Optimum size of dental practices is another aspect of availability. The evidence suggests that practices with 2 or 3 dentists are more efficient than solo practices. However, large group practices appear only to be of equal or even less efficiency than small group practices. The accessibility of dental care is influenced by the geographical location of practices, the convenience of obtaining care during non-working hours, the reduction and dissemination of information on dental fees and, most importantly, the beliefs of people concerning their oral health status. The appropriateness of care concerns the impact of different services on improving oral health. Relatively little clinical research has been published on the costs and benefits of different dental services. The acceptability of dental care concerns both patients who visit the dentist and the larger society. Studies show that patients who visit the dentist are generally satisfied with the care they receive. Societal attitudes about the dental care system have not received much attention. Although social science research on the dental care delivery system is at an early stage of development, some data exist which are relevant to optimizing the practice of dentistry.

Consumer Behavior↗
PubMed1980

Total hemolytic complement values in normal and diseased dog populations.

The optimum conditions for handling and storage of canine sera for total hemolytic complement assays were assessed. Sera from 113 normal dogs and 217 clinical admissions to the University of Pennsylvania Veterinary Hospital were assayed for total hemolytic complement levels. Normal sera had a mean value of 185 CH50 units. Sera from animals with systemic lupus erythematosus and hemorrhagic gastroenteritis, had significantly lower mean levels of complement than the normal group. Sera from dogs with generalized demodectic mange, tumors, various inflammatory diseases, hypothyroidism, seborrhea, and rheumatoid arthritis had values significantly higher than the normal population.

Animals↗
PubMed1977

Can polymorphism be maintained by selection favouring an intermediate optimum phenotype?

Populations of Drosophila melanogaster containing the special chromosome, M-5, were subjected to artificial selection to canalise scutellar bristle phenotype at four bristles. At the end of the experiment allele frequencies at three enzyme loci were measured. In the selected population, these frequencies were found to have diverged from their starting values less than would have been predicted on the basis of random genetic drift. This was not found in control populations or in populations selected for low bristle number.

Alleles↗
PubMed1988

Factors influencing the optimum sex ratio in a structured population.

W. D. Hamilton (1967, Science 156, 477-488) calculated the optimum sex-ratio strategy for a population subdivided into local mating groups. He made three important assumptions: that the females founding each group responded precisely to the number of them initiating the group; that ail broods within a group matured synchronously; and that males were incapable of dispersing between groups. We have examined the effects of relaxing each of these assumptions and obtained the following results: (1) When broods mature asynchronously the optimum sex ratio is considerably more female biased than the Hamiltonian prediction. (2) Increasing male dispersal always decreases the optimum female bias to the sex ratio, but it is of particular interest that when moderate levels of dispersal are coupled with asynchrony of brood maturation then the optimum strategy is relatively insensitive to changes in foundress number. (3) When females cannot precisely determine the number of other foundresses initiating the group then the optimum strategy is almost exactly the strategy appropriate to a group of average size. These effects can be most easily understood in terms of local parental control (LPC) of the sex ratio. Through LPC a founding female can alter the mating success of her sons by altering the sex ratio of her brood. Asynchrony in the maturation of broods within a group increases the control that a founding female has over the mating success of her sons, whereas male dispersal reduces it. We have shown that the role of LPC and the role of inbreeding, which favors a female-biased sex ratio in haploidiploid species, are independent and that their effects can be combined into a single general formula r = (1-(r2/z2) E(alpha z/alpha r]/(1 + I). The concept of LPC can also be used to interpret two factors which have been proposed to select for the Hamiltonian sex ratios: local mate competition is LPC acting through sons; and sib mating is LPC acting through daughters.

Animals↗
PubMed1996

Interactions between magnesium and vitamin D: possible implications in the immune system.

Evidence clearly shows that magnesium and vitamin D [1 alpha, 25-dihydroxyvitamin D3; 1,25(OH)2D3] independently affect numerous aspects of the immune system. Although no reports of interactive effects on components of immunity have been found, there is evidence that the two nutrients interact in other biosystems, sometimes involving calcium. Furthermore, this paper identifies numerous places in common where both magnesium and vitamin D reportedly affect immune function. Fundamental sites for possible interaction within the immune system include cell transformation, regulation of the cell cycle, stabilization of nuclear DNA/chromatin, production of reactive oxygen species (ROS), and effects on enzymatic and hormonal actions. The presence of different functional, chemical forms of both of the nutrients within biological systems, and the availability of synthetic drug relatives of both to introduce into such systems, complicate interactive studies because such differing forms may not necessarily interact similarly or interact at all within the immune system or elsewhere. Regardless, there are compelling reasons to believe that examining interactions between magnesium and vitamin D within the immune system could prove rewarding, especially since the physiological statuses of both nutrients in human populations are less than optimum. Such human populations include the elderly whose immune function may be compromised.

Animals↗
PubMed1990

Optimal population control with uncertain output.

"This note has shown how the techniques of stochastic control theory can be used to analyze the impact of uncertainty about non-labour inputs on optimal population control expenditure. While we have chosen very simple structure, it has allowed us to isolate the channels through which uncertainty affects the optimal plan, in this case causing expected expenditure on control to rise more slowly or fall more rapidly than its deterministic counterpart. Given the long-term implications of changes in population growth at any instant, and the stochastic nature of the environment in which control decisions are made, it is likely that useful insights could be obtained by extending the stochastic control approach to more complicated population control structures."

Demography↗