Fast life in cold water: Diamesa incallida (Chironomidae)

Development times of Diamesa incallida and its numbers of generations per vear were studied using in situ reanngs in conjunction with continuous collection of egg masses from the field The evidence suggested that the crenophilous D incallida laid eggs throughout the year and produced eight to ten generations per year, depending on water temperature (76°C to 80°C) This is the first proof for a muitivoltine Diamesinae as well as for continuous egg laying behaviour by a non–troprcal chironomid The comparatively large mature larvae (96 mm, 710 μ.g a f d weight) and the numerous generations per year indicate that D incallida is a highly productive component of crenal communities The importance of rearing chironomids over a sufficient number of generations is emphasized as a basis for the reliable interpretation of field data     

Transgenerational consequences of acute antenatal stress in pregnant rats

The aim of the present study was to investigate the effects of acute hypobaric hypoxia in early organogenesis on three following generations including pregnant females (FO) and two generations of their posterity (F1 and F2). Animals of all generations mentioned above demonstrated marked changes in motor and exploratory activity as well as in anxiety level while the litter of F1 and F2 generations showed also changes in learning ability. Besides, acute hypobaric hypoxia interfered in maternal behavior of females of the FO and F1 generations. The revealed changes kept till pubertal period. Possible mechanisms of gestational stress influence are discussed.     

Development of 0-methylhydroxylamine induced mutations causing resistance to 8-azaguanine in Chinese hamster cells]

The dependence of the yield of mutations of the resistance to 8-azaguanine induced with 0-methylhydroxylamine on the number of cell generations that have passed by the time of the creation of selective conditions and the existence of a phenotypic lag period is established. The highest rate of mutations is found after 8-azaguanine treatment in two generations. As the number of generations increased, the number of detectable mutations decreased. A dependence is observed between the induced mutation frequency and death of cells as the latter are transferred to selective conditions after two generations. In experiments on induced mutagenesis, one can obtain more exact quantitative characteristics by introducing a selective agent into the cell suspension but not by treating growing cells in colonies.     

Generational shape shifting: changes in egg shape and size between sexual and asexual generations of a cyclically parthenogenic gall former

Successive generations of multivoltine species experience selection specific to the spatiotemporal environments encountered that may lead to adaptive divergence in reproductive traits among generations. To compare reproductive effort within and between generations, appropriate volumetric models, selected on the basis of the analysis of egg shape, are required to estimate the sizes (volumes) of individual eggs. We assessed the shape and estimated the volume of individual eggs produced by the temporally and spatially segregated sexual and asexual generations of the gall former, Belonocnema treatae Mayr (Hymenoptera: Cynipini: Cynipidae). Egg shape, indexed as the difference between the polar and equatorial axes of the ellipsoidal eggs, was independent of egg size, but differed between generations. The relationship of egg shape and female body size within and between generations confirmed that egg shape is an intrinsic property of each generation. Generational differences in egg shape then informed the selection of volumetric models to estimate egg size. We modeled asexual generation eggs as both spheres and prolate spheroids, and sexual generation eggs as both cylinders and prolate spheroids. Choice of volumetric model changed estimates of egg size within the asexual generation by 23% and within the sexual generation by 50%. Comparisons between generations based on the above models produced estimated differences in egg volume that ranged from 16 to 114%. In both generations, a prolate spheroid was the most parsimonious model of egg volume. Based on this model, sexual generation eggs averaged 43% larger than asexual generation eggs. The increased size of sexual eggs was achieved via conservation of the egg’s equatorial axis and elongation of the polar axis. The shift in egg shape between sexual and asexual B. treatae is the first documented dimorphism in an egg characteristic expressed between generations of a cyclically parthenogenic organism.     

Thermal aspects of electromagnetic field interactions with bound calcium ions at the nerve cell surface

This paper examines the cost of meiosis in a species with an alternation of sexual and asexual generations (e.g. Daphnia), by means of calculations of the survival probabilities of mutant genes causing patterns of wholly asexual reproduction. It is shown that the survival probabilities of such mutations are lower with an alternation of sexual and asexual generations than with an initial population which reproduces exclusively sexually. The survival probabilities decrease as the number of asexual generations within each reproductive cycle increases. It is argued that these results imply a lower than usual cost of meiosis when there is an alternation of generations, and that asexual reproduction cannot simply be equated with vegetative growth of a single multicellular organism.     

Spontaneous and Ethyl Methanesulfonate-Induced Mutations Controlling Viability in DROSOPHILA MELANOGASTER. II. Homozygous Effect of Polygenic Mutations

Polygenic mutations affecting viability were accumulated on the second chromosome of Drosophila melanogaster by treating flies with EMS in successive generations. The treated chromosomes were later made homozygous and tested for their effects on viability by comparison of the frequency of such homozygotes with that of other genotypes in the same culture. The treated wild-type chromosomes were kept heterozygous in Pm/+ males by mating individual males in successive generations to Cy/Pm females. The number of generations of accumulation was 1 to 30 generations, depending on the concentration of EMS. A similar experiment for spontaneous polygenic mutations was also conducted by accumulating mutations for 40 generations. The lower limit of the spontaneous mutation rate of viability polygenes is estimated to be 0.06 per second chromosome per generation, which is about 12 times as high as the spontaneous recessive lethal mutation rate, 0.005. EMS-induced polygenic mutations increase linearly with the number of treated generations and with the concentration of EMS. The minimum mutation rate of viability polygenes is about 0.017 per 10(-4)m, which is only slightly larger than the lethal rate of 0.013 per 10(-4) m. The maximum estimate of the viability reduction of a single mutant is about 6 to 10 percent of the normal viability. The data are consistent with a constant average effect per mutant at all concentrations, but this is about three times as high as that for spontaneous mutants. It is obvious that one can obtain only a lower limit for the mutation rate, since some mutants may have effects so near to zero that they cannot be detected. The possibility of measuring something other than the lower limit is discussed. The ratio of the load due to detrimental mutants to that caused by lethals, the D/L ratio, is about 0.2 to 0.3 for EMS-induced mutants, as compared to about 0.5 for spontaneous mutants. This is to be expected if EMS treatment produces a large fraction of small deletions and other chromosome rearrangements which are more likely to be lethal.     

Progeny selection for agronomic characters in early generations of a potato breeding programme

 Repeatabilities of progeny means, and the univariate cross prediction method were used to study the effectiveness of progeny selection for agronomically important characters in early generations of potato (Solanum tuberosum L.) breeding. The study was based on 90 progenies (72 crosses+18 selfs) evaluated for three successive generations, i.e. seedling, first clonal and second clonal generations. Repeatabilities of progeny means were measured as correlation coefficients between generations. In the univariate cross prediction method, progeny means and within-progeny standard deviations were used to calculate the proportions of clones exceeding the target values, and correlation coefficients between generations for predicted and observed proportions of clones, were calculated. Population means varied from generation to generation. Correlation coefficients between generations for progeny means for most of the characters were significant, but moderate. These were higher than the correlation coefficients between predicted and observed proportions of clones exceeding the target values. The possibility of using progeny means as a selection parameter to reduce the number of genotypes to be examined in later stages by rejecting the poor crosses in seedling generation is discussed. Received: 8 January 1997/Accepted: 28 February 1997     

Seasonal allocation of energy to respiration, growth and reproduction in the freshwater clams, Pisidium variabile and P. compressum (Bivalvia: Pisidiidae)

SUMMARY. 1. The ecological energetics of the pisidiid clams, Pisidium variabile and P. compressum , from permanent ponds in southwestern Ohio were studied from July 1978 to July 1980. Productivity (P; as g C m⁻² yr ⁻¹) was 1.82 (0.80 and 1.02 for the spring and autumn generations) and 4.22 (2.69 and 1.53 for the spring and autumn generations) for P. variabile and P. compressum , respectively.
2. The average biomass (B; as g C m⁻²) of P. variabile was 0.54 (0.30 and 0.24 for the spring and autumn generations) and of P. compressum 1.09 (0.69 and 0.40 for the spring and autumn generations). P:B ratios for the spring and autumn generations of P. variabile were 2.7 and 4.2 and of P. compressum 3.9 and 3.8, which are below those reported for other iteroparous invertebrates.
3. Reproductive effort (Re:Px100) was 5.1 and 5.7 for the generations of P. variabile and 7.7 and 8.8 for the generations of P. compressum. These low values relative to other molluses can be attributed to a viviparous mode of reproduction and exposure to local environmental variability. In addition, the differences between the reproductive efforts of the spring and autumn generations of both species can be ascribed to season of birth and altometric constraints on reproductive capacity.
4. The data from this and related studies on pisidiid clams are used to generate several hypotheses concerning the evolution of life cycles in the family: (1) reproductive effort is limited by allometric constraints on clam size; (2) individuals of different ages can have different demographies and physiological rate functions; and (3) current one-dimensional life history theories are largely inappropriate when dealing with an organism that has a wide range of phenotypic responses to environmental variability as well as complex age structure.     

SUBCULTIVATIONS, SPLITS, DOUBLINGS, AND GENERATIONS IN CULTURES OF HUMAN DIPLOID FIBROBLASTS

Mathematical expressions are provided relating subcultivations to population doublings and population doublings to generations. Account is made for the increasing number of cells which do not attach upon subcultivation as well as the increasing number of non-dividers. The expressions reconcile published differences in longevity and reveal that the in vitro lifetime of human diploid cells measured in cell generations is far greater than previously suspected.     

A note on effective population size with overlapping generations

A simple derivation is given for a formula obtained previously for the effective size of random-mating populations with overlapping generations. The effective population size is the same as that for a population with discrete generations having the same variance of lifetime family size and the same number of individuals entering the population per generation.     

Large-scale systematic study on stability of the Ds element and timing of transposition in rice

Activator/Dissociation (Ac/Ds) transposon mutagenesis is a widely used tool for gene identification; however, several reports on silencing of the Ac/Ds element in starter lines and in stable transposants question the applicability of such an approach in later generations. We have performed a systematic analysis on various aspects of the silencing phenomenon in rice (Oryza sativa ssp. japonica cv. Nipponbare). High somatic and germinal transposition frequencies observed in earlier generations were maintained as late as T4 and T5 generations; thus the propagation of parental lines did not induce transposon silencing. Moreover, the stably transposed Ds element was active even at the F5 generation, since Ac could remobilize the Ds element as indicated by the footprint analysis of several revertants. Expression of the bar gene was monitored from F3 to F6 generations in >1,000 lines. Strikingly, substantial transgene silencing was not observed in any of the generations tested. We analyzed the timing of transposition during rice development and provide evidence that Ds is transposed late after tiller formation. The possibility, that the independent events could be the result of secondary transposition, was ruled out by analyzing potential footprints by reciprocal PCR. Our study validates the Ac/Ds system as a tool for large-scale mutagenesis in rice, since the Ds elements were active in the starter and insertion lines even in the later generations. We propose that harvesting rice seeds using their panicles is an alternative way to increase the number of independent transposants due to post-tillering transposition.     

Negative ��GHIs,�� the Right to Health Protection, and Future Generations

The argument has been made that future generations of human beings are being harmed unjustifiably by the actions individuals commit today. This paper addresses what it might mean to harm future generations, whether we might harm them, and what our duties toward future generations might be. After introducing the “Global Health Impact” (GHI) concept as a unit of measurement that evaluates the effects of human actions on the health of all organisms, an incomplete theory of human justice is proposed. Having shown that the negative GHIs of our current generation cause unfair harm to future generations, I argue that each human being must be allocated a fair threshold of negative GHIs that should not be exceeded. By emphasising the need to consider all the GHIs of human actions, the theory of human justice developed here is highly relevant to evaluate human actions that might affect future generations, for example those related to climate change.     

携带IL-2/NK4双基因减毒沙门氏菌TPIN的遗传稳定性研究

对携带IL-2/NK4双基因减毒沙门氏菌TPIN的遗传稳定性进行研究。将TPIN连续传40代,取10代、20代、30代、40代菌落进行鉴定,包括菌落和菌体的形态、质粒的纯度和浓度、目的基因片段、双酶切结果及转染人肝癌细胞(HepG2)后目的基因体外表达活性。结果表明,每10代的菌落和菌体形态一致,其所含质粒的纯度和浓度在传代过程中无明显变化,PCR扩增的目的基因条带大小一致,双酶切鉴定结果正确,转染HepG2细胞后,每代间所表达目的蛋白浓度无明显差异。TPIN作为消化道肿瘤的生物治疗药物,在遗传方面有较好的稳定性,可进一步进行大量生产。     

Transformation of expression intensities across generations of Affymetrix microarrays using sequence matching and regression modeling

The utility of previously generated microarray data is severely limited owing to small study size, leading to under-powered analysis, and failure of replication. Multiplicity of platforms and various sources of systematic noise limit the ability to compile existing data from similar studies. We present a model for transformation of data across different generations of Affymetrix arrays, developed using previously published datasets describing technical replicates performed with two generations of arrays. The transformation is based upon a probe set-specific regression model, generated from replicate measurements across platforms, performed using correlation coefficients. The model, when applied to the expression intensities of 5069 shared, sequence-matched probe sets in three different generations of Affymetrix Human oligonucleotide arrays, showed significant improvement in inter generation correlations between sample-wide means and individual probe set pairs. The approach was further validated by an observed reduction in Euclidean distance between signal intensities across generations for the predicted values. Finally, application of the model to independent, but related datasets resulted in improved clustering of samples based upon their biological, as opposed to technical, attributes. Our results suggest that this transformation method is a valuable tool for integrating microarray datasets from different generations of arrays.     

The influence of climatic changes on range expansion and phenology of the Colorado potato beetle (Leptinotarsa decemlineata,Coleoptera, Chrysomelidae) in the territory of Russia

Analysis of expansion of the potential range of the Colorado potato beetle Leptinotarsa decemlineata Say and shifts of the zones with different number of generations per season was carried out using cartographic modeling. The shifts were caused by the climate changes in Russia observed in recent decades. The annual sum of effective mean daily air temperatures was selected as the main criterion which determines both the suitability of the area for the Colorado potato beetle and the number of generations that can be produced in one season. The main range expansion was observed in the east direction, and the greatest changes took place during expanding of the zones with the possible development of one or two generations. The boundaries of the zone where development of three generations is possible changed to a lesser degree.     

应用微卫星标记对稀有(鱼句)鲫封闭群建群过程的遗传监测

以采自四川省汉源县的野生稀有鮈鲫(Gobiocypris rarus)50对为建群原代(P0),采用最佳避免近交法建立了封闭群Ihb:IHB。应用11对微卫星引物对原代、F1—F4代传代亲鱼进行了遗传多样性监测。11个微卫星位点在稀有鮈鲫野生型封闭群共发现等位基因57个,各位点平均等位基因数5.2个、平均有效等位基因数3.3个、平均多态信息含量0.5282。封闭群各代平均期望杂合度为0.5553—0.5742,平均多态信息含量范围为0.5060—0.5318,平均观察等位基因数、平均有效等位基因数、平均观察杂合度、平均期望杂合度、平均多态信息含量在各代之间均无显著性差异(P>0.05)。各代间的遗传相似性在0.99以上,遗传分化系数FST为0.0008(P>0.05),基因频率也无显著性差异(P>0.05)。监测结果表明,Ihb:IHB保持了野生种群的遗传多样性,建群传代过程中未出现显著的遗传分化,符合实验动物封闭群的要求,可以作为一个实验动物的新品系。     

Polymorphic fundatrices in thimbleberry aphid — ecology and maintenance

The thimbleberry aphid,Masonaphis maxima (Mason) lives on patches of plants that support 3,4 or 5 generations depending on site and weather. The life cycle requires sexual females and males to produce overwintering eggs. The eggs hatch in the spring to produce the first ’fundatrix’ generation; subsequent generations are produced parthenogenically. Males and other morphs are produced by wingless virginoparae, but sexual females are produced by ’gynoparae’, a winged morph that is specialized to produce only sexual females. The fundatrices have no indication of the number of generations that the plants will support in the current year. There are two fundatrix types that coexist in different ratios depending on the number of generations supported by the patch the previous year. One type produces sexual females in generations 3 and 5, and males in generations 4 and 5; the other type produces sexual females in generations 4 and 5, and males in generations 3, 4 and 5. The dimorphism adapts the aphid to its heterogeneous and somewhat unpredictable environment. The role of sex in the maintenance of the dimorphism is discussed. This is the first report of fundatrix polymorphism and consequent differential sex expression in aphids.     

Replicated selection for 21-day pupa weight of Tribolium castaneum

Summary Response to upward selection in 10 replicate lines was linear through 15 generations, had slowed considerably in many lines by generation 23 and continued in other lines through 30 generations. The lines tended to group into those which responsed slowly during early generations and continued to respond through later generations and those which gave rapid early response and very low response later coupled with marked reduction in fitness. Response to downward selection was similar for 3 replicate lines but only 50% as great as that for the high lines. Response declined more rapidly in the low lines due to reduced fitness, declining selection differentials and a marked drop in phenotypic variance.     

Effect of phenotypic switching on the biological properties and susceptibility to chlorhexidine in Candida krusei ATCC 14243

Phenotypic switching is characterized as a virulence factor of Candida spp. This study was carried out to evaluate the phenotypic switching ability of C.?krusei ATCC 14243 and to determine its effect on the biological properties, adherence capacity and susceptibility towards chlorhexidine digluconate (CHX). To induce switched generations C.?krusei was cultured under nitrogen-depleted growth conditions by adding phloxine B. These phenotypically switched colonies were designated as the 1st generation. Subsequent sub-culturing was performed to produce the 2nd, 3rd and 4th switched generations. The recovery of the 3rd generation was the highest at 85.7% while that of the 4th generation was lower at 70.8%, and the recovery of the 1st and 2nd generations gradually reduced to 46.6% and 36.4%, respectively. All generations of C.?krusei were susceptible towards CHX. The unswitched C.?krusei was the most susceptible but the least adherent to coated hard surfaces. The 2nd generation was the least susceptible, but with the highest adherent ability. The minimum inhibition concentration and minimal fungicidal concentration of C.?krusei of all generations were determined at 0.4?mg?mL(-1) . These observations suggest that the switching activity of C.?krusei induces changes to its biological properties and susceptibility towards CHX.