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PubMed2004

Adaptive changes in harvested populations: plasticity and evolution of age and size at maturation.

We investigate harvest-induced adaptive changes in age and size at maturation by modelling both plastic variation and evolutionary trajectories. Harvesting mature individuals displaces the reaction norm for age and size at maturation toward older ages and larger sizes and rotates it clockwise, whereas harvesting immature individuals has the reverse qualitative effect. If both immature and mature individuals are harvested, the net effect has approximately the same trend as when harvesting immature individuals only. This stems from the sensitivity of the evolutionary response, which depends on the maturity state of harvested individuals, but also on the type of harvest mortality (negatively or positively density dependent, density independent) and the value of three life-history parameters (natural mortality, growth rate and the trade-off between growth and reproduction). Evolutionary changes in the maturation reaction norm have strong repercussions for the mean size and the density of harvested individuals that, in most cases, result in the reduction of biomass--a response that population dynamical models would overlook. These results highlight the importance of accounting for evolutionary trends in the long-term management of exploited living resources and give qualitative insights into how to minimize the detrimental consequences of harvest-induced evolutionary changes in maturation reaction norms.

Adaptation, Biological↗
PubMed1997

Weight-length relationships and reproduction of bream (Abramis brama L.) in Keszthely Bay of Lake Balaton.

The weight-length relationships of bream (Abramis brama L. 1758, family Cyprinidae) were studied in Lake Balaton, Hungary, Fish were randomly collected with a gill net from Keszthely bay between March and November 1995. The condition of bream was investigated monthly, using morphometric parameters of the body, fecundity estimations, and gonadosomatic indices (GSI). The weight-length relationships show that the body weight of bream increased at an approximately 3.4 times higher rate than its length (b = 3.41). The GSI of females were always higher than those of the males. The GSI values of females reached their maximum (14.76-22.22) from March to May. Egg diameter is positively correlated with the spawning months, as demonstrated by the relationship found between egg diameter and GSI (r = 0.94; P < 0.001) Fecundity estimates exhibited a linear relationship to length and weight.

Animals↗
PubMed1996

Multicenter clinical trial on the efficacy and acceptability of a single contraceptive implant of nomegestrol acetate, Uniplant.

Uniplant, a single Silastic implant containing nomegestrol acetate, provides contraceptive efficacy for one year. Uniplant use for one year was studied in 1,803 healthy women of reproductive age, enrolled from 10 centers in 9 countries, after informed consent. Implants were placed subdermally either in the upper arm or in the gluteal region. Two-hundred-seventy-six subjects discontinued prior to completing one year of study. Cumulative discontinuation rate at 12 months was 15.72%. Medical reasons for discontinuation were principally menstrual-related. Fifteen pregnancies occurred during the one year study period, resulting in a 12-month net cumulative pregnancy rate of 0.94%. Approximately 56% of subjects using Uniplant had bleeding patterns similar to normal menstruation. Results from this study confirm that Uniplant is an efficient, well tolerated, 12-month contraceptive implant, with the advantage of easier insertion and removal of the single implant compared to other multiple implant methods.

Adult↗
PubMed2004

Morbidity effects on productivity and profitability of stocker cattle grazing in the Southern Plains.

Effects of bovine respiratory disease (BRD) on stocker cattle systems are unknown under extensive rangeland environments. Three experiments were conducted to test the hypothesis that BRD-based morbidity is a major factor affecting the productivity and profitability of stocker cattle grazing Southern Plains rangelands. In Exp. 1 (658 male calves; average BW = 231 kg), 17% of the cattle were treated for BRD <8 d, 6% for 8 to 14 d, and 8% for >14 d. Morbid cattle had lower ADG than did healthy cattle (P < 0.10). Cattle requiring 14 d of pharmaceutical therapy gained less than cattle having <14 d therapy (P < 0.01). In Exp. 2, (279 steers and bulls; average BW = 216 kg), the ADG by steers (0.74 kg x animal(-1) x d(-1)) was greater (P < 0.05) than by bulls castrated after arrival (0.64 kg x animal(-1) x d(-1)). Castration after arrival led to a 13.5% loss in daily gain and a 10.3% loss in season-long gain. More (P < 0.05) bulls castrated after arrival (60%) were morbid compared with steers (28%). In Exp. 3, 633 heifers (average BW = 251 kg) were used to test the effects of morbidity on weight gain and reproduction. Heifers with lower initial weights exhibited increased (P < 0.05) morbidity. Heifers requiring two or more antibiotic treatments gained 0.03 kg/d less (P < 0.10) than did healthy heifers and had lower (P < 0.05) conception rates (66 vs. 81%). Conception rate in twice-treated heifers was 19% less than healthy heifers. Morbid heifers conceived 0.6 mo later (P < 0.05) than healthy heifers. Under the conditions of Exp. 1 and Exp. 2, morbidity decreased net returns 9.7 to 21.3% per animal. Adjusted gross returns per animal in Exp. 3 for replacement heifers were 3 to 7.8% less for morbid heifers.

Animal Husbandry↗
PubMed2004

Periodic abstinence in developing countries: an assessment of failure rates and consequences.

It is estimated that 27 million couples, representing 2.6% of all couples in the reproductive span, use periodic abstinence (PA). Using data from 15 national surveys in low and middle-income countries, this article assesses characteristics of PA users, knowledge of the fertile period, accidental conceptions while using PA and the reproductive consequences of these conceptions. Current users of PA (predominantly the simple calendar variant) tend to be more educated and urban than users of other methods. The method is preferred by young single women and older married women. The proportion of users with correct knowledge of the timing of ovulation ranges from 8% to 91%, with a median value of 62%. The median 12-month gross failure rate was 24 per 100 episodes. Net of other predictors of failure, correct knowledge of the timing of ovulation was associated with a 12% decrease in failure probabilities. Couples who experienced PA failure were more likely than couples who experienced failure with another method to carry the pregnancy to term. Nevertheless, PA still contributes to one-sixth of all abortions (or miscarriages) following contraceptive failure.

Adolescent↗
PubMed2004

Effects of mercury on the life table demography of the rotifer Brachionus calyciflorus Pallas (Rotifera).

Mercury is highly toxic to a variety of aquatic organisms including zooplankton. The functioning of freshwater ecosystems can be altered if rotifers, being a natural food link between phytoplankton and fish larvae, are contaminated by mercuric compounds. In order to detect age-specific responses of the rotifer Brachionus calyciflorus to mercury toxicity (5 nominal concentrations as chloride viz. 0, 0.000625, 0.00125, 0.0025 and 0.005 mg l(-1)), we used the standard life table method at two different food (Chlorella vulgaris) levels (0.5 x 10(6) and 1.5 x 10(6) cells ml(-1)). Data indicated that increase in mercury concentration had an increasingly intense negative effect on many of the life history variables, while at higher food levels, its impact was less. A nearly rectangular survivorship pattern was obtained in controls, especially at higher food levels. This trend gradually changed to a steep fall as the concentration of the heavy metal in the medium increased from 0 to 0.005 mg l(-1). At any given food density, increase in the mercury concentration resulted in decreased age-specific reproduction. A maximum of 3.5 offspring female(-1) was observed in controls at higher food density. The average lifespan varied from 6 to 8 days at low food level, depending on the heavy metal concentration in the medium. The corresponding values at high food level varied from 8 to 12 days. Regardless of mercury concentration in the medium, gross and net reproductive values varied from 10 to 33 and 4 to 19 offspring female(-1). The longest generation time (about 9 days) of B. calyciflorus was obtained at 1.5 x 10(6) cells ml(-1) food density in control, while the shortest was 5 days at low food level and high (0.005 mg l(-1)) mercury concentration in the medium. Depending on the food level and heavy metal concentration in the medium, the rate of population growth (r) varied from 0.32 to 0.62 d(-1). In general, higher food level resulted in higher r. Except generation time, all other derived variables were significantly influenced by food level and the heavy metal concentration in the medium.

Analysis of Variance↗
PubMed2006

Physiology of intermittent feeding: integrating responses of vertebrates to nutritional deficit and excess.

Food intakes of wild animals may not match their requirements for nutrients and energy but may vary between periods of nutritional excess (hyperphagia) and nutritional deficit (hypophagia) at timescales that vary from days to months. We present a simple model of feeding patterns and requirements of vertebrates. Frequent fasts and high intakes are typical of endothermic predators and migratory birds, whereas slow cycles and long deficits typify feeding patterns of ectothermic predators and ungulates in seasonal environments. We propose that hyperphagia is constrained by the ability to increase processes of digestion, absorption, intermediary metabolism, net deposition in tissue, and excretion to match loads of digesta and metabolites. Hyperphagia on high-quality diets is limited by the clearance of metabolites, whereas digestive tract capacity and flow limit consumption of low-quality diets. Of all digestive strategies, small omnivores with simple digestive systems may be the most tolerant of frequent hyperphagia. Tolerance of hypophagia favors large endogenous stores or low mass-specific rates of metabolism and reproductive output. Large animals may be most able to sustain reproduction during prolonged deficits in seasonal environments. Responses to excessive and deficient intakes of food are constrained by the length of the feeding cycle. Animals adapted to short feeding cycles may be best suited to unpredictable food supplies but at the energetic cost of maintaining spare capacity for digestion and absorption. Predictions of the response to food disruption are best evaluated in the context of body size, nutritional physiology, and life history of the species and the time for internal response.

Animal Nutritional Physiological Phenomena↗
PubMed2003

[Establishment and analysis of laboratory population life table of Trichogramma dendrolimi developed on Antherea pernyi eggs].

The laboratory population life table of Trichogramma dendrolimi Matsumura developed on the eggs of Antherea pernyi was established by calculating the survival rate at immature stage and the adult reproduction. The survival rate of egg, larval and pupa was 1.00, 0.9186 and 0.8895, respectively, and the emergence rate of pupa was 0.8668. The total mortality rate at immature stage reached to 30%, which was a great difference from those developed on small host eggs. Each Trichogramma female could lay about 86 eggs on one Antherea pernyi egg. The index of Trichogramma population trend was 54.48. Analysis on the relationships among intrinsic rate of natural increase (rm), net production rate (R0) and index of population trend (I) showed that the R0 and I had the same biological meaning, and rm could be calculated with I value.

Animals↗
PubMed2003

Patterns of local migration and their consequences in a rural Ethiopian population.

AIMS: In the context of the Butajira Rural Health Programme (BRHP) in Ethiopia, which has maintained demographic surveillance in selected communities since 1987, this paper investigates patterns of migration and their consequences within that population over a ten year period 1987-1996. METHODS & RESULTS: Based on observations of over 336,000 person-years in nine rural villages and one small town, 48% of individuals migrated in or out of the study area at some stage, as recorded in monthly household visits. There was a net incidence of migration into the urban area, particularly among young adults. Mortality was higher among residents compared with in-migrants, with rates of 10.5 (95% CI 7.5 to 14.9) and 8.2 (95% CI 5.8 to 11.7) per 1,000 person-years respectively after adjustment for age, sex and area of residence, a rate ratio of 1.3. Fertility among in-migrant and resident women was similar, at rates of 0.26 and 0.28 births per reproductive year respectively. CONCLUSIONS: The causes of the observed differences in mortality are not clear, though they may be partly due to self-selection effects among migrants, and may have important implications for future health policy and planning in Ethiopia and other similar settings.

Adolescent↗
PubMed1999

Epilepsy in women: the science of why it is special.

Epilepsy is a common neurological disorder that may be affected by reproductive hormones and may complicate reproductive health. Many women with epilepsy experience changes in seizure frequency and severity with changes in reproductive cycles, including at puberty, over the menstrual cycle, with pregnancy and at menopause. Ovarian steroids alter neuronal excitability at the membrane and in the genome. Altered protein synthesis as a consequence of changes in RNA mediated gene transcription is one mechanism for steroid mediated effects on excitability. These genomic effects are delayed and sustained. In contrast, membrane effects are immediate and short duration. These effects are mediated at both the GABA-A and NMDA receptors. Estrogen also dynamically alters synaptic connectivity. Estrogen enhances excitability and lowers the seizure threshold, whereas progesterone enhances inhibition and increases the seizure threshold. In experimental models of epilepsy, estrogen is proconvulsant and progesterone is anticonvulsant. The net effect of these steroid actions is to alter neuronal excitability over physiological cycles. Some epilepsy syndromes are expressed or worsened at puberty. One third to one half of women with epilepsy have catamenial seizure patterns, with seizures most likely to occur in the perimenstrual period and at ovulation. More research is needed to understand the effects of menopause on epilepsy. Antiepileptic drugs may exacerbate the risk of reproductive endocrine disorders in women with epilepsy. Fertility rates are lower for women with epilepsy. Women with epilepsy are more likely to have anovulatory menstrual cycles, abnormal pituitary LH release and altered ovarian steroid concentrations. Polycystic ovaries are detected more often in women with epilepsy, particularly those on valproate. Treatment of hormone sensitive seizures relies on standard AEDs. Small trials suggest that adjunctive progesterone therapy is sometimes helpful. The newer AEDs, gabapentin and lamotrigine may have some advantages for women with epilepsy. These drugs do not alter levels of steroid hormones and do not interfere with effectiveness of hormonal contraception. Experience in pregnancy is limited. The dynamic effects of hormones on seizure expression and of seizures on reproductive health complicate the management of epilepsy in women. Newer AEDs may offer advantages for women with epilepsy in the reproductive years.

Epilepsy↗
PubMed2005

A spreadsheet-based model demonstrating the nonuniform economic effects of varying reproductive performance in Ohio dairy herds.

A spreadsheet-based model was developed to estimate the economic effect of varying reproductive performance in dairy herds. Scenarios were created to model an average cow with respect to production, herd lifetime, and reproductive events. Average milk yield per day of life as well as lifetime calf and replacement heifer production were examined. Additional inputs representing milk, feed, semen, calf, and salvage prices were used to calculate net cash flow for each day of herd life for the average cow in a scenario. Economic comparison of different scenarios was accomplished using an equivalent annual cash flow (annuity) methodology.Herd performance measures and prices representative of Ohio dairy herds were used to establish a baseline average cow that had a 160-d calving-to-conception interval [days open (DO)]. Alternative scenarios that differed from baseline in DO, annual culling rate, and feed and milk prices were created to characterize the effects of changes. Under scenario inputs representative of typical Ohio dairy herds, the model indicated that a lower annual culling rate (25%) was preferable to higher annual culling rates (34 or 45%). The model estimated maximum average milk yield per day of life to occur at 110 DO. At 34% annual culling rate, calves and replacement heifers produced per lifetime declined as DO increased; beyond 150 DO, the modeled cow produced less than 1 replacement heifer per lifetime. The model also estimated a loss of $1.37 per cow per year for a 1-d increase in DO beyond 160 d. At 20% higher feed and milk prices, the model estimated a loss of $1.52 per cow per year; at 20% lower feed and milk prices, the model estimated a loss of $1.23 per cow per year. Furthermore, the model suggested that the loss associated with a 1-d increase in DO changed as DO changed. Using baseline inputs, the model calculated losses for a 1-d increase of $0.44 per cow per year at 130 DO and $1.71 per cow per year at 190 DO. The nonuniform nature of the cost of additional DO is important to veterinarians and producers. The implication is that inefficient reproduction becomes marginally more costly to producers as performance declines and warrants increased attention. Conversely, marginal benefits of improved reproduction decrease as performance improves. Herds with strong reproductive performance have less opportunity to capture economic benefits of improvement.

Animals↗
PubMed1997

Influence of environmental and plant factors on canopy photosynthesis and transpiration of apple trees.

We estimated carbon and water flows, canopy conductance and the assimilation/transpiration ratio of fruiting and non-fruiting apple trees grown in the field, from daily gas exchange measurements taken during the summer with a whole-canopy enclosure device. The relationships between photosynthetic and transpirational responses and environmental conditions were also investigated, as well as the role of canopy conductance in controlling carbon dioxide and water vapor exchange. Light-saturated net photosynthetic rates, which were higher for the fruiting canopy than for the non-fruiting canopy, showed a general decrease in the afternoon, particularly for the non-fruiting canopy, compared with rates in the morning. When light was not limiting, the afternoon decrease in net photosynthesis appeared to be regulated more by non-stomatal factors than by changes in canopy conductance. Canopy conductance, which was higher for the fruiting canopy than for the non-fruiting canopy, may actively regulate photosynthetic activity and may also be modulated by feedback control in response to assimilation capacity. We conclude that adjustments in canopy conductance, which were partially dependent on the vegetative-reproductive status of the tree, control the equilibrium between photosynthesis and transpiration. We also demonstrated that whole-canopy chambers can be used to estimate photosynthetic and transpirational responses thereby overcoming the difficulty of scaling these physiological responses from the leaf to the whole-canopy level.

Journal Article↗
PubMed2001

Profiles of adaptation in two similar viruses.

The related bacteriophages phiX174 and G4 were adapted to the inhibitory temperature of 44 degrees and monitored for nucleotide changes throughout the genome. Phage were evolved by serial transfer at low multiplicity of infection on rapidly dividing bacteria to select genotypes with the fastest rates of reproduction. Both phage showed overall greater fitness effects per substitution during the early stages of adaptation. The fitness of phiX174 improved from -0.7 to 5.6 doublings of phage concentration per generation. Five missense mutations were observed. The earliest two mutations accounted for 85% of the ultimate fitness gain. In contrast, G4 required adaptation to the intermediate temperature of 41.5 degrees before it could be maintained at 44 degrees. Its fitness at 44 degrees increased from -2.7 to 3.2, nearly the same net gain as in phiX174, but with three times the opportunity for adaptation. Seventeen mutations were observed in G4: 14 missense, 2 silent, and 1 intergenic. The first 3 missense substitutions accounted for over half the ultimate fitness increase. Although the expected pattern of periodic selective sweeps was the most common one for both phage, some mutations were lost after becoming frequent, and long-term polymorphism was observed. This study provides the greatest detail yet in combining fitness profiles with the underlying pattern of genetic changes, and the results support recent theories on the range of fitness effects of substitutions fixed during adaptation.

Bacteriophage phi X 174↗
PubMed1982

A randomized, double-blind study of two combined and two progestogen-only oral contraceptives.

A randomized double-blind study of two combined oral contraceptives and two progestogen-only oral contraceptives was conducted using the same protocol at WHO Collaborating Centres for Clinical Research in Human Reproduction in Bombay and Ljubljana of the 518 women admitted to the trial, 123 received mestranol 50 micrograms + norethisterone 1mg (MES 50 + NET 1); 137 received ethinyl estradiol 30 micrograms + levonorgestrel 150 micrograms (EE 30 + LNG 150); 130 received norethisterone 350 micrograms/NET 350); and 128 received levonorgestrel 30 micrograms (LNG 30). At one year, between 52.6 and 61.0 percent of those recruited had discontinued oral contraceptive use for all reasons, and by two years, between 70.5 and 76.5 percent had discontinued the treatment. These rates did not differ between the four treatment groups. However, discontinuation rates for all medical reasons at one and two years, and at two years pregnancy rates and discontinuation rates for bleeding disturbances, were significantly lower in the EE/LNG preparation. The groups receiving the MES/NET, LNG and NET had similar pregnancy rates, discontinuation rates for all medical reasons and all bleeding disturbances. There were two ectopic pregnancies among the 22 pregnancies in the progestogen-only groups. Discontinuation because of headache, dizziness and other central nervous system symptoms were significantly more common in those receiving MES/NET compared to EE/LNG. In contrast, discontinuation for gastro-intestinal disturbances were significantly higher in the EE/LNG combined preparation. Bleeding disturbances in the first few cycles tended to be higher in NET than in the LNG group. The data suggest that greater consideration be given to the benefits and risks of including progestogen-only oral contraceptives in the family planning programmes of some countries.

Adolescent↗
PubMed2004

Population genetics of tumor suppressor genes.

Cancer emerges when a single cell receives multiple mutations. For example, the inactivation of both alleles of a tumor suppressor gene (TSG) can imply a net reproductive advantage of the cell and might lead to clonal expansion. In this paper, we calculate the probability as a function of time that a population of cells has generated at least one cell with two inactivated alleles of a TSG. Different kinetic laws hold for small and large populations. The inactivation of the first allele can either be neutral or lead to a selective advantage or disadvantage. The inactivation of the first and of the second allele can occur at equal or different rates. Our calculations provide insights into basic aspects of population genetics determining cancer initiation and progression.

Alleles↗
PubMed1980

A circuit for safe diagnostic electrical stimulation of the human brain.

An electronic circuit for controlled electrical stimulation of the human brain has been designed to optimize safety in charge transfer from electrodes to brain and to eliminate the likelihood of unwanted currents from the neurostimulator resulting from component failure. The circuit schematics feature the following designs: (1) a highly accurate and versatile rate generator 0.5 p.p.s. to 99 in increments of 0.5 p.p.s., (2) symmetrically-biphasic lead and lag pulses of 100 musec duration, (3) photo-isolated driver amplifiers with accurate waveform, reproduction, (4) true biphasic passive-current regulators driven by an isolated battery supply voltage for switch-selectable currents of 0.25 to 5 ma or variable current regulation, (5) accurate current and voltage waveform monitors that isolate the stimulating electrodes from the monitors, and (6) capacity-coupled outputs to guarantee no net D.C. component at the end of each biphasic pulse. Relay-switching circuits are also shown that allow sequential stimulation and recording from one or several electrodes. This neurostimulator has been in use for over two years without evidence of electrolytic damage at identifiable electrode tips. The utility of simultaneous stimulation of several different electrodes at safe charge levels is described.

Amygdala↗
PubMed2003

Inbreeding pattern and reproductive success in a rural community from Galicia (Spain).

The present paper is based on information on marital patterns and reproductive performance (reconstituted families) in the rural community of Los Nogales, Galicia, Spain. Biodemographic data were used to analyse temporal changes and structure of consanguinity in the population, as well as consanguinity versus reproductive success. Of 2347 marriages celebrated between 1871 and 1977, 5.15% were between relatives (up to third degree). The population's inbreeding coefficient was above the Spanish average after 1890, and levels were high during the first part of the 20th century. A possible underestimation of inbreeding coefficients is attributed to the elevated frequency of extramarital births occurring in the Los Nogales population (13.47%). The structures of consanguineous matings, expressed as C22/C33 and C33/C44, turned out to be 0.86 and 0.82 respectively. Regarding migration, before 1920 consanguinity increased, but net migration was negative. In the period 1920-1929 consanguinity began to decrease, prior to maximum emigration. As for reproductive success, information from 1503 reconstituted families shows that complete fertility was slightly higher among consanguineous families despite a greater infant mortality. Lower infertility in consanguineous matings, as well as lower age at marriage and first maternity, could explain the above results.

Adolescent↗
PubMed1997

Evaluation of a nutritional strategy to increase ovulation rate in merino ewes mated in late spring-early summer.

A nutritional strategy for increasing ovulation rate in Merino ewes mated in late spring-early summer was evaluated on two commercial farms. The strategy used the 'ram effect' to induce oestrus in seasonally anoestrus ewes and supplementary feeding of lupin grain six days prior to oestrus to increase ovulation rate. Ewes that had been isolated from rams for 6 weeks were exposed to vasectomised rams for 2 weeks and then mated to fertile rams for 6 weeks. Feeding 500 g lupins/head/day for 14 days commencing 12 days after the introduction of vasectomised rams, increased the number of ovulations from 126 to 146 per 100 ewes exposed to rams (P < 0.05). This increase was reflected in an improvement in fecundity (lambs born per ewe lambing; P < 0.05) but not fertility (ewes lambing per ewe mated to rams). Net reproductive performance (the product of fertility, fecundity and lamb survival) was increased by 11 lambs weaned per 100 ewes exposed to rams due to lupin supplementation at mating.

Animal Nutritional Physiological Phenomena↗