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PubMed1998

Requisite mutational load, pathway epistasis and deterministic mutation accumulation in sexual versus asexual populations.

A measure of the equilibrium load of deleterious mutations is developed that explicitly incorporates the level of genome-wide linkage disequilibrium. This measure, called the requisite mutational load, is based on the minimal net reproductive rate of the least mutated class necessary to prevent the deterministic mutation accumulation. If this minimal net reproductive rate is larger than ecological or physiological constraints allow, then: a) the population is driven to extinction via deterministic mutation accumulation, or b) a mutational Red-Queen ensues with adaptation counterbalancing mutation accumulation. Two population parameters determine the requisite mutational load: a) the equilibrium strength of selection, measured as a selection gradient, and b) the equilibrium opportunity for selection, measured as the variance in number of mutations per genome. The opportunity for selection is decomposed into the accumulation of mutations (average number per genome) and the level of genome-wide linkage disequilibrium. Recombination can substantially reduce the requisite mutational load, compared to clonal reproduction, when there is buffering and/or reinforcing epistasis and also when there is positive assortative mating for fitness. Recombination is advantageous because it reduces the negative (variance reducing) linkage disequilibrium induced by beneficial epistasis. The functional form of the expression for requisite mutational load illustrates why epistasis within pathways, i.e., among closely interacting genes, is a powerful alternative to genome-wide truncation selection, as a means of reducing mutational load.

Animals↗
PubMed1994

[An analysis of Korean women's reproductivity].

An analysis of reproductivity is mainly concerned with the measurement of net force of fertility expressed in terms of a generation rather than in a given year. The present study examined current trends of Korean Women's reproductivity interpreting general reproduction and net reproduction rates, intrinsic rate of natural increase and mean length of gestation. The data used for this analysis were drawn from the national fertility surveys from 1970 through 1990 conducted by the Korea Institute for Population and Health. The figures of the present study revealed that the reproduction rates of Korea during the last 20 years decreased from 2.22 in 1970 to 0.71 in 1990 and net reproduction rates also dropped from 1.9 to 0.69 during the same period of time. Furthermore, from this study, it is noticed that the replacement level of fertility had been reached since the early 1980s. The intrinsic rate of natural increase as measure of population growth under existing conditions of fertility and mortality and free of the influence of the current age distribution, is computed. The level of rate was not much changed and was 0.3 in 1970 compared with 0.25 in 1990, which is still higher than other developed countries. The mean age of mother at the birth of their daughters defined as the length of generation has been slightly changed from 23.9 in 1971 to 25.8 in 1990.

Age Factors↗
PubMed2006

Effects of microclimatic changes caused by deforestation on the survivorship and reproductive fitness of Anopheles gambiae in western Kenya highlands.

Land use changes have been suggested as one of the causes for malaria epidemics in the African highlands. This study investigated the effects of deforestation-induced changes in indoor temperature on the survivorship and reproductive fitness of Anopheles gambiae in an epidemic prone area in the western Kenya highlands. We found that the mean indoor temperatures of houses located in the deforested area were 1.2 degrees C higher than in houses located in the forested area during the dry season and 0.7 degrees C higher during the rainy season. The mosquito mortality rate was highly age-dependent regardless of study site or season. Mosquitoes that were placed in houses in the deforested area showed a 64.8-79.5% higher fecundity than those in houses located in the forested area, but the median survival time was reduced by 5-7 days. Female mosquitoes in the deforested area showed a 38.5-40.6% increase in net reproductive rate and an 11.6-42.9% increase in intrinsic growth rate than those in the forested area. Significant increases in net reproductive rate and intrinsic growth rate for mosquitoes in the deforested area suggest that deforestation enhances mosquito reproductive fitness, increasing mosquito population growth potential in the western Kenya highlands. The vectorial capacity of An. gambiae under study was estimated at least 106% and 29% higher in the deforested area than in the forested area in dry and rainy seasons, respectively.

Animals↗
PubMed2006

The effect of temperature and humidity on the bionomics of six African egg parasitoids (Hymenoptera: Trichogrammatidae).

The life table statistics of six native Kenyan species/strains of Trichogramma and Trichogrammatoidea were established using a factitious host Corcyra cephalonica, Stainton (Lepidoptera: Pyralidae), at eight different temperatures (10, 15, 20, 25, 28, 30, 32 and 35 degrees C) and two humidity levels (40-50 and 70-80%). The objective was to select insects with superior attributes for augmentative release against lepidopteran pests in horticultural crops. Both temperature and humidity affected developmental time and life table parameters of the parasitoids but temperature played a more critical role. Developmental time was inversely related to temperature. The intrinsic and finite rates of increase increased with temperature up to 30 degrees C. Both net reproduction rate and intrinsic rate of increase were higher at the lower humidity. Temperature inversely affected generation time of parasitoid strains regardless of the relative humidity. Two strains of Trichogramma sp. nr. mwanzai collected from both low and medium altitudes and Trichogrammatoidea sp. nr. lutea from the mid-altitudes, were better adapted to both low and high temperatures than the other strains, as indicated by the high intrinsic and net reproductive rates, at both humidity levels. These three strains appear to be promising candidates for augmentation biocontrol against the African bollworm Helicoverpa armigera in Kenya.

Animals↗
PubMed2005

Effect of salinity stress on the life history variables of Branchipus schaefferi Fisher, 1834 (Crustacea: Anostraca).

BACKGROUND: Freshwater anostracans inhabit ephemeral water bodies in which as the water level decreases due to evaporation the salt concentration increases. Thus, for most anostracans salinity becomes the major stress factor. RESULTS: We tested five concentrations of NaCl (0 to 8 g/l) on the life table demography of Branchipus schaefferi fed Chlorella (alga). Age-specific survivorship curves of male and female B. schaefferi showed nearly a similar pattern in that increased salt concentration resulted in decreased survivorship. The age-specific reproduction (m(x)) of females showed several peaks of cyst production at 0 and 1 g/l salinity while in treatments containing salt at 4 or 8 g/l, there were fewer peaks. Average lifespan, life expectancy at birth, gross and net reproductive rates, generation time and the rate of population increase were all significantly influenced by the salt concentration in the medium. The highest value of net reproductive rate (970 cysts/female) was in treatments containing 0 g/l of salt, while the lowest was 13 cysts/female at 8 g/l. The rate of population increase (r) varied from 0.52 to 0.32 per day depending on the salt concentration in the medium. CONCLUSION: The low survival and offspring production of B. schaefferi at higher salinity levels suggests that this species is unlikely to colonize inland saline water bodies. Therefore, the temporary ponds in which it is found, proper conservative measures must be taken to protect this species.

Journal Article↗
PubMed2002

Evolution of flowering strategies in Oenothera glazioviana: an integral projection model approach.

The timing of reproduction is a key determinant of fitness. Here, we develop parameterized integral projection models of size-related flowering for the monocarpic perennial Oenothera glazioviana and use these to predict the evolutionarily stable strategy (ESS) for flowering. For the most part there is excellent agreement between the model predictions and the results of quantitative field studies. However, the model predicts a much steeper relationship between plant size and the probability of flowering than observed in the field, indicating selection for a 'threshold size' flowering function. Elasticity and sensitivity analysis of population growth rate lambda and net reproductive rate R(0) are used to identify the critical traits that determine fitness and control the ESS for flowering. Using the fitted model we calculate the fitness landscape for invading genotypes and show that this is characterized by a ridge of approximately equal fitness. The implications of these results for the maintenance of genetic variation are discussed.

Biological Evolution↗
PubMed1985

Lifetime (seven years) production of 1/4 and 1/2 Finnish Landrace ewes from Rambouillet, Targhee and Columbia dams under range conditions.

Lifetime lamb and wool production of 1/4 and 1/2 Finnish Landrace (Finn) crossbred ewes in comparison with local purebred controls was evaluated under range conditions. A total of 1,234 ewe lambs, representing nine breed groups, were first exposed to breeding at 7 mo of age and subsequently retained with no artificial culling, except for debilitating unsoundness, through 7 yr of production. Mating was to Suffolk sires. Differences among pooled breed groups (1/4 Finns, 1/2 Finns and purebreds) generally were not significant for ewe viability to lambing, percentage of lambs born alive and lamb viability to weaning; nor were differences significant for fertility except among yearlings (12 mo at lambing) where 1/4 and 1/2 Finn fertility exceeded that of purebreds by 217 and 278%, respectively. However, for prolificacy, Finn-crosses were consistently superior to purebreds at all seven ages; 1/4 and 1/2 Finns averaged 24 and 48% higher, respectively, than purebreds. Further, Finn-cross ewes clearly excelled purebreds (P less than .05) in the two overall measures of reproduction--net reproductive rate and weight of lamb weaned. The superiority was sustained through all ages and averaged (over ages 2 through 7 yr) 29 and 49% for net reproductive rate and 24 and 41% for weight weaned, for 1/4 and 1/2 Finns, respectively. Conversely, for wool weight, purebreds were consistently superior at all ages; the lifetime averages of 1/4 and 1/2 Finn fleeces were only 90 and 77% as high, respectively, as those of purebreds. It was concluded, however, that the loss in value of wool production associated with Finn breeding was economically of much less importance than the gains made in weight of lamb weaned. The use of 1/4 and 1/2 Finn-crosses involving the above adapted domestic breeds increased the net value of lifetime production by approximately 18 and 29%, respectively.

Animals↗
PubMed2001

Effects of salinity, temperature and food level on the demographic characteristics of the seawater rotifer Synchaeta littoralis Rousselet.

A strain of the seawater species Synchaeta littoralis, isolated from a Spanish Mediterranean coastal salt marsh, was cultured in the laboratory and fed with the alga Tetraselmis sp. The effect of three salinities (25 per thousand, 30 per thousand and 35 per thousand), two temperatures (20 degrees C and 25 degrees C) and two food levels (75,000 and 150,000 cells ml(-1)) on demographic parameters was studied using a life table approach. Average lifespan (LS) ranged between 4.0 and 7.3 days, net reproductive rate (R(0)) between 4.2 and 9.1 offspring per female, and intrinsic growth rate (r) between 0.50 and 0.95 day(-1). Salinity and temperature had a significant negative effect (***p<0.001) on both average lifespan (LS) and net reproductive rate (R(0)). Nevertheless, S. littoralis grew adequately at 35 per thousand (average value of r=0.67 day(-1)). Intrinsic growth rate also increased with temperature due to the lower value of the generation time (ranged between 2.3 and 3.8 days in all assays). Food level only had a significant negative effect (***p<0.001) on R(0). The experiments designed allowed us to know the basic demographic parameters of S. littoralis.

Journal Article↗
PubMed1991

Effects of inbreeding on reproduction and wool production of Rambouillet, Targhee, and Columbia ewes.

Because of a traditional interest in inbreeding as a tool for breed improvement, it was desirable to evaluate the effects of inbreeding on the most important products of the sheep industry, lamb and wool production. The data for this study were based on 13,807 ewe and 16,470 lamb records from Rambouillet (R), Targhee (T), and Columbia (C) sheep collected over 9 or 10 yr from 54 inbred lines. Average inbreeding of the lambs and ewes involved was near 25 and 20%, respectively. The combined effects of lamb's and dam's inbreeding reduced litter weight weaned at 120 d approximately .5 kg for each percentage of increase in inbreeding in every breed. For ewes and lambs of average inbreeding, the reductions relative to noninbred ewes amounted to 12.4, 10.3, and 11.3 kg for R, T, and C, respectively. The reductions constituted declines in weight weaned per ewe of 34, 25, and 28%. Similarly, net reproduction rate (lambs weaned per ewes put into breeding) was reduced more than one percentage point for each percentage of increase in inbreeding, with net declines at average inbreeding of 31.7, 23.5, and 25.7 percentage points for each breed, respectively. These reductions were equivalent to reductions in net rate of 29, 20, and 23%. The combined effect of lamb and dam inbreeding reduced weaning weight by 3.5, 2.6, and 2.2 kg, which constituted reductions of 10, 7, and 6%, respectively. Reduced weaning weight was approximately 30% as important as reduced net reproduction rate in contributing to the decline in litter weight weaned. Effects on fleece weight were curvilinear and amounted to reductions of .35, .18, and .00 kg, respectively, at levels of average inbreeding; however, Columbia fleece weights declined rapidly at levels exceeding 20% for ewes. Potential selection differentials were reduced 16% at inbreeding levels of 25 and 20% for lambs and dams, respectively, and 62% at levels of 55 and 50%. The average economic loss per ewe in value of production was estimated at $17 for average inbreeding and as high as $36 for inbreeding approaching 50%. It seems that the use of inbreeding as a tool for improving productive merit in sheep is much more certain to be a detriment, economically and genetically, than an advantage.

Animals↗
PubMed2005

[Effects of corn cultivar on Tetranychus truncatus ehara (Acarina: Tetranychidae) population parameters].

The laboratory study at 28 degrees C showed that on four different corn cultivars, the durations of ovum, nymph and pre-oviposition, adult longevity, fecundity, egg production per day, net reproductive rate (R0), finite rate of increase (lambda), intrinsic rate of increase (rm), mean generation time (T), and the days needed to double population size (DDP) of Tetranychus truncatus were significantly different. The hatching rate on Zea mays cv. Zhongdan 2, Nongda 108, Chidan 202 and Badan 3 was 95.8%, 94.0%, 90.0% and 84.0%, and the survival rate on these cultivars was 90.5%, 86.0%, 84.0%, and 72.0%, respectively. All the survival curves were of Deevey I . The net reproductive rate (R0) was the highest on Zhongdan 2, and the lowest on Badan 3. The mite displayed a decreasing preference in order of Zhongdan 2 > Nongda 108 > Chidan 202 > Badan 3.

Animals↗
PubMed2005

Toxicity and hazard assessment of fipronil to Daphnia pulex.

Hazard assessments based on two measures of toxicity were conducted for the water flea, Daphnia pulex (Leydig) exposed to the insecticide, fipronil. The measures of toxicity obtained were 48 h acute lethal concentration estimates, and a direct measure of population growth rate, the 10-day instantaneous rate of increase (r(i)). Additionally, life tables were developed after exposure to several concentrations to tease out the apparent sublethal effects of this insecticide to D. pulex. The acute LC(50) was estimated to be 0.0156 (0.0088-0.083) mg/L. In the 10-day population growth rate study, extinction of D. pulex populations occurred after exposure to 0.08 mg/L of fipronil, which was equivalent to the 48 h acute LC(75). The NOEC and LOEC for population size after a 10-day exposure to fipronil were 0.03 and 0.05 mg/L, respectively. An expected environmental concentration (EEC) in freshwater lakes/ponds based on an application rate of 250 mg ai/ha (recommended rate for use in Tephritid fruit fly control programs) was estimated to be 0.00017 mg/L. Hazard assessments were developed by dividing the EEC by the LC(50) and NOEC for population size. The assessments based on the LC(50) and NOEC for population size were 0.011 and 0.0057, respectively, indicating that fipronil does not pose a hazard to D. pulex when applied at the rates recommended for control of Tephritid fruit flies. Life tables were developed after exposure to two insecticide concentrations and a control. Exposure to 0.015 mg/L, the approximate 48 h acute LC(50), resulted in only a slight decrease in the net reproductive rate (R(o)), birth rate (b), and intrinsic rate of increase (r(m)) and an increase in generation time (T), death rate (d), and doubling time (DT) compared to the control. Exposure to 0.03 mg/L, the approximate 48 h acute LC(60), and NOEC in the 10-day study, resulted in a 57% decline in the net reproductive rate, a 1.45-fold decrease in birth rate, a 1.5-fold decrease in the intrinsic rate of increase, a 6-day increase in generation time, a 4-fold increase in death rate, and a 1.5-fold increase in doubling time. The stable age distribution (after 60 days) of D. pulex changed after exposure to fipronil. Increasing concentrations of fipronil resulted in a decrease in the percentage of individuals in the first, second, third, and fourth juvenile stages, an increase in the adult stage, and no change in the adolescent stage. These results indicate that certain concentrations of fipronil approaching the LC(50) can negatively affect population parameters of D. pulex, but that EECs, at least for fruit fly control, should be lower than the concentration necessary to cause damage.

Animals↗
PubMed2002

Applications of Perron-Frobenius theory to population dynamics.

By the use of Perron-Frobenius theory, simple proofs are given of the Fundamental Theorem of Demography and of a theorem of Cushing and Yicang on the net reproductive rate occurring in matrix models of population dynamics. The latter result, which is closely related to the Stein-Rosenberg theorem in numerical linear algebra, is further refined with some additional nonnegative matrix theory. When the fertility matrix is scaled by the net reproductive rate, the growth rate of the model is $1$. More generally, we show how to achieve a given growth rate for the model by scaling the fertility matrix. Demographic interpretations of the results are given.

Female↗
PubMed2005

[Effects of glyphosate on life histroy characteristics of freshwater rotifer Brachionus calyciflorus].

The life table study on the life history characteristics of freshwater rotifer Brachionus calyciflorus under effects of different concentrations glyphosate showed that glyphosate had significant effects on the embryonic developmental time, duration of juvenile and reproductive periods, average lifespan, net reproductive rate, and intrinsic population increasing rate of the rotifer. The embryonic developmental time was significantly lengthened when exposed to 3 and 8 mg x L(-1) glyphosate, the juvenile period began to be lengthened significantly when exposed to 3 mg x L(-1) glyphosate, while the net reproductive rate and intrinsic population increasing rate decreased significantly when the rotifer was exposed to 8.00 and 10.50 mg x L(-1) glyphosate, respectively. Among all the parameters, intrinsic population increasing rate was the most sensitive parameter which could be used in monitoring the effects of glyphosate on the life history characteristics of B. calyciflorus.

Animals↗
PubMed2001

Fitness parameters and DNA effects are sensitive indicators of copper-induced toxicity in Daphnia magna.

This study compared the effects occurring at molecular and population levels in Daphnia magna exposed to copper concentrations in the range of 15-120 microg/l. The qualitative and quantitative modifications arising in random amplified polymorphic DNA (RAPD) profiles as a measure of DNA effects were compared with a number of key ecological fitness parameters, namely, the age-specific survival, age-specific fecundity, net reproductive rate, and intrinsic rate of population increase. Results suggested that growth, reproduction, and most of the fitness parameters as well as genomic template stability (a qualitative measure reflecting changes in RAPD profiles) were significantly affected at copper concentrations of 90 and 120 microg/l. Among the fitness parameters, the age-specific fecundity and net reproductive rate were the most sensitive parameters of toxicity. Changes in RAPD patterns generally occurred at copper concentrations of 90 and 120 microg/l, but with one primer, changes significantly arose at all copper concentrations. Overall, molecular and population parameters compared well and represented a sensitive means to measure toxicity induced by copper in Daphnia magna. In conclusion, the measurement of parameters at both molecular and population levels is valuable for investigating the specific effects of agents interacting with DNA. Ultimately, this methodology may allow the ecotoxicological examination of the link between molecular alterations and measurable adverse effects at higher levels of biological organization.

Animals↗
PubMed2001

Euseiusfinlandicus (Acari: Phytoseiidae) as a potential biocontrol agent against Tetranychus urticae (Acari: Tetranychidae): life history and feeding habits on three different types of food.

Life history and reproductive parameters of the generalist predatory mite Euseius (Amblyseius) finlandicus (Oudemans) were studied in the laboratory at 25 +/- 1 degrees C, with a 16L:8D photoperiod and 60 +/- 15% RH, to investigate its response to different food sources: an eriophyid mite Aceria sp., tulip pollen Tulipa gesnerana L., and two-spotted spider mite Tetranychus urticae Koch. Total developmental time of the immature stages was the shortest on eriophyid mites, followed by pollen, and then spider mites. Fecundity was highest on pollen (43.69 eggs; 1.63 eggs/female/day), then eriophyid mites (39.73 eggs; 1.37 eggs/female/day) and lowest on spider mites (18.16 eggs; 0.80 eggs/female/day). Intrinsic rate of increase (Rm), net reproductive rate (Ro) and finite rate of increase (lambda) followed the same pattern [pollen (0.168, 27.96 and 1.183, respectively), eriophyid mites (0.153, 20.81 and 1.167), spider mites (0.110, 9.44 and 1.119)]. Mean generation time (days) was the shortest on pollen (19.90), followed by eriophyid mites (20.02), and then spider mites (20.59). Average spider mite larvae consumed by E. finlandicus during immature stages were 9.18 for males and 11.85 for females. Adult E. finlandicus females consumed an average of 166.38 spider mite protonymphs during adult stage compared to an average of 66.55 by males. The number of prey protonymphs consumed per day by females was highest in the oviposition period, lower in the pre-oviposition period and the lowest in the post-oviposition period. The eriophyid mite as a prey recorded the shortest developmental time, while pollen as food recorded the highest oviposition rate in E. finlandicus. The potential of this predator as a biocontrol agent against T. urticae is discussed.

Animals↗
PubMed1993

Ten-year linear trends in reproduction and wool production among inbred and noninbred lines of Rambouillet, Targhee, and Columbia sheep.

To investigate the value of creating inbred lines for genetic improvement of sheep, 54 inbred, 1 randombred control, and 3 noninbred control lines were evaluated for lamb and wool production. Results were based on 19,438 dam and 23,625 lamb records from Rambouillet (R), Targhee (T), and Columbia (C) sheep collected over 9 yr (for T and C) and 10 yr (for R), starting in 1954. Average inbreeding in the inbred lines during the period was near 25% for lambs and 20% for ewes. The general trend in inbred lines for litter weight weaned (120 d) and number weaned (net reproductive rate), per ewe exposed to breeding, was downward as inbreeding increased. Trends in fleece weight generally also were down, regardless of concomitant increases in body weight. Declines were most pronounced in two lines developed by rapid inbreeding. Reproductive merit in the R and C noninbred controls also declined, but the declines were less than those for most inbred lines. Although the T noninbred control declined in fleece weight, trends for fleece weight in the R and C controls were positive and significantly different from the negative trends in the inbred lines. For the randombred control, slight downward trends in litter weight and number weaned were less (P < .05) than those for most inbred lines, indicating genetic declines in these traits for most inbred lines. Direct selection for an index of overall phenotypic merit, recurrent selection for combining ability for overall merit, and direct selection for body type, clean fleece weight, or staple length were all ineffective in preventing a decline in reproductive merit. Ending means (last 2 yr of production) revealed that litter weight weaned in the control groups of each breed was clearly superior to that in most inbred lines. Controls also were typically superior for fleece and body weight. Not one of the 54 inbred lines was superior (P < .05) to its respective noninbred control in weight of lamb weaned or net reproductive rate. Only four of the inbred lines were superior to the noninbred controls in fleece weight. These results, after at least 23 yr of development for most lines, reflect little encouragement for the costly development of many inbred lines for the purpose of improving lamb and wool production, especially when using the above selection criteria.

Animals↗
PubMed2004

Demography, life history, and social structure in Propithecus diadema edwardsi from 1986-2000 in Ranomafana National Park, Madagascar.

Prosimian lemurs differ fundamentally from anthropoid primates in many traits related to social structure. By exploring the demography of Milne-Edwards' sifakas (Propithecus diadema edwardsi), and comparing it to other well-studied primates, we explore the effect of demographic and life-history factors on social structure. Specifically, we compare lemur survivorship and fertility patterns to two published composite models: one created for New World and another created for Old World monkeys. Using longitudinal data collected on individual Propithecus diadema edwardsi from four study groups from 1986-2000 in Ranomafana National Park, Madagascar, we quantify 1) group composition, 2) birth seasonality, 3) interbirth interval, 4) life-table values, and 5) population growth estimates. The mortality, survivorship, and life-expectancy schedules indicate high infant and juvenile mortality. Fertility remains high until death. The intrinsic rate of increase and net reproductive rate indicate a shrinking population. We suggest that high mortality rather than low fertility causes the observed population decline. While sifaka survivorship closely resembles New World patterns, fertility resembles Old World patterns, i.e., like New World monkeys, few sifakas survive to reproductive age, and those that do, reproduce at a slow rate resembling the Old World pattern. This necessarily impacts social structure. An adult sifaka at the end of her lifespan will have one only daughter who survives to reproductive age, compared to 3.4 for New World or 2.7 for Old World monkeys. Demography limits the formation of large kin-based groups for sifakas, and survivorship and fertility patterns do not easily permit sifakas to form large same-sex family groups.

Animals↗