Minimum frequency of compound autosomes inDrosophila melanogaster to achieve chromosomal replacement in cages

A genetic insect control technique is examined that involves the replacement of a population of individuals carrying standard chromosomes by those bearing compound autosomes, which also incorporate factors such as conditional lethal mutations for subsequent control. A variety of compound 2 and 3 lines from the fruit flyDrosophila melanogaster was tested in cages at initial compound to standard ratios that approached the unstable genetic equilibrium point. The lowest ratio that gave successful displacement of standards by compounds was 4 compounds: 1 standard. To evaluate the effciency of the various methods, a comparison is drawn between the data from the compound competition experiments and those from alternative genetic techniques for pest control.     

Exploring the Potential of Compound;free-Arm Combinations of Chromosome 2 in DROSOPHILA MELANOGASTER for Insect Control and the Survival to Pupae of Whole-Arm Trisomies

Genetic tests of second-chromosome compound;free-arm combinations ("free arms") in Drosophila melanogaster indicate that the egg hatch is approximately 50% that of standard lines and adult recovery is approximately 40%. Free-arm strains are genetically isolated from both compound-chromosome lines and standards.

A large proportion of the hybrid progeny arising from crosses between free arms and standards or free arms and compounds, survive to the pupal stage. Cytological examinations reveal that these hybrids are trisomic for one arm of chromosome 2. Such hybrid progeny may place an added constraint upon the competition between free-arm and standard strains by competing for food, but not contributing to the adult population. The fitness data, the genetic isolation characteristic and the possible impact of hybrid progeny all suggest that free arms may prove to be a valuable genetic tool for insect population control. Preliminary cage-competition experiments to test this prediction have demonstrated that free arms are able to displace standards at ratios as low as 3:1, which is close to the theoretical equilibrium predicted by the fitness data (2.5:1).

     

Karyotype displacement in a laboratory population of the two spotted spider mite Tetranychus urticae (Koch): Experiments and computer simulations

Three different strains, homozygous for a radiation induced structural chromosome mutation (T), exhibiting negative hererosis, were tested for their ability to displace the standard (wild-type) karyotype from experimental populations. The experimental populations were initiated by mixing fertilized females of both a T strain and the standard strain at different ratios. Two of the T strains showed the ability to displace the standard karyotype if the initial frequency of the T karyotype was at least 0.65. The additional release of T males into the experimental population accelerated considerably the process of displacement of the standard karyotype, especially if the initial T karyotype frequency was 0.65.A computer model for simulating the process of population displacement in Tetranychus urticae was developed. The model accounts for variation in developmental time and for the age dependency of variables related to fitness. The simulations showed a good correlation with the experimental results. A system analysis on the sensitivity of the model output to varying different population parameters demonstrated that especially the relative number of males produced by a T strain and the female developmental rate were of significant importance to the population displacement ability of a T strain. The negative influence of genetic markers on general fitness and various aspects of practical application of the method are discussed.     

Control of Rhizoctonia solani and Cotton Seedling Disease by Laetisaria arvalis and a Mycophagous Insect Proisotoma minuta (Collembola)

Population changes in Pseudocercosporella herpotrichoides with and without fungicide selection A conidium mixture of W (wheat-type) and R (rye-type) strains of Pseudocercosporella herpotrichoides (W:R = 1:1) was incubated on PD-agar without fungicide or amended with the imidazole prochloraz or the triazole cyproconazole. The W:R ratio was assessed over four generations using the different benomyl sensitivity of the strains as marker. In untreated mixtures, the R strain completely dominated the population already after two generations. Similarly, in cyproconazole-treated mixtures, the R strain increased to 100% after the second generation, whereas in prochloraz-treated mixtures the R strain either followed the same pattern as in untreated mixtures or fluctuated around the initial proportion of 50% over four generations. The W and R strains displayed different fitness properties. The average hyphal growth rate was 8.5 mm/10 d and 4.5 mm/10 d for the W and the R strains, respectively; the sporulation capacity was 80 and 400 conidia/colony, respectively, for the two strains. The different fitness resulted in a strong dominance of the R strains both in vitro and in field populations towards the end of the vegetation period. This shift towards R-dominance occurred about equally fast with or without fungicide selection.     

The effect of immigration on genetic control

Summary Immigration by wild type flies into an established compound chromosome control zone was studied in the laboratory using discrete generation population cages. Immigration rates of less than 10 % per generation by virgin migrants were unlikely to disrupt the zone. However, the zone could be disrupted by immigration rates of 0.5 % if the migrants had mated. The curvilinear relationship between the number of generations to fixation of the migrant genotype and the immigration rate suggested a possible equilibrium between immigration rate and the maintenance of a control zone. -The importance of the results to the strategy of a particular control program is emphasized, as is the need for an integrated multi-disciplinary approach to insect pest management.     

Survival of colour-polymorphic Eristalis arbustorum hoverflies in semi-field conditions

1. The theory on adaptive phenotypic plasticity assumes different fitness optima in different environments. To demonstrate these fitness differences in the field or under laboratory conditions can be difficult.
2. The size of the coloured patches on the abdomen of Eristalis arbustorum varies with rearing temperature. At low temperatures small patches develop and at higher temperatures larger patches develop. Consequently, the colour patch size varies seasonally.
3. To study the relative fitness of two extreme phenotypes in abdominal coloration in the summer, a total of 591 laboratory-reared flies were released in six large population cages. As a measure of fitness, survival was estimated.
4. In all replicate cages the survival of the pale phenotypes was higher than that of the dark phenotypes, indicating a higher fitness for the pale flies under summer conditions.
5. The fat content of flies reared under identical conditions to those released in the cages was measured. Pale flies had ≈ 0·7 mg more fat than dark flies (± 25% extra fat). However, it is argued that this difference in fat reserves could not have been the only cause of the observed difference in survival.
6. The results are discussed in relation to mimicry and thermoregulation.     

Mitochondrial DNA haplotype frequencies in natural and experimental populations of Drosophila subobscura.

The evolution of Drosophila subobscura mitochondrial DNA has been studied in experimental populations, founded with flies from a natural population from Esporles (Majorca, Balearic Islands, Spain). This population, like other European ones, is characterized by the presence of two very common (>96%) mitochondrial haplotypes (called I and II) and rare and endemic haplotypes that appear at very low frequencies. There is no statistical evidence of positive Darwinian selection acting on the mitochondrial DNA variants according to Tajima''s neutrality test. Two experimental populations, with one replicate each, were established with flies having a heterogeneous nuclear genetic background, which was representative of the composition of the natural population. Both populations were started with the two most frequent mitochondrial haplotypes, but at different initial frequencies. After 13 to 16 generations, haplotype II reached fixation in three cages and its frequency was 0.89 by generation 25 in the fourth cage. Random drift can be rejected as the force responsible for the observed changes in haplotype frequencies. There is not only statistical evidence of a linear trend favoring a mtDNA (haploid) fitness effect, but also of a significant nonlinear deviation that could be due to a nuclear component.     

Drastic fitness loss in human immunodeficiency virus type 1 upon serial bottleneck events

Muller's ratchet predicts fitness losses in small populations of asexual organisms because of the irreversible accumulation of deleterious mutations and genetic drift. This effect should be enhanced if population bottlenecks intervene and fixation of mutations is not compensated by recombination. To study whether Muller's ratchet could operate in a retrovirus, 10 biological clones were derived from a human immunodeficiency virus type 1 (HIV-1) field isolate by MT-4 plaque assay. Each clone was subjected to 15 plaque-to-plaque passages. Surprisingly, genetic deterioration of viral clones was very drastic, and only 4 of the 10 initial clones were able to produce viable progeny after the serial plaque transfers. Two of the initial clones stopped forming plaques at passage 7, two others stopped at passage 13, and only four of the remaining six clones yielded infectious virus. Of these four, three displayed important fitness losses. Thus, despite virions carrying two copies of genomic RNA and the system displaying frequent recombination, HIV-1 manifested a drastic fitness loss as a result of an accentuation of Muller's ratchet effect.     

Evolutionarily stable sex ratios and sex allocations

The paternal fitness of a sexual individual is equated with the fitness of those eggs of its potential mates which it is able to fertilize. This property enables the total sexual fitness of individuals to be expressed in terms of female gamete contributions in separate equations for a cosex (an individual in a population composed of a single sexual class which combines male and female functions) and for parents in a dioecious population. The general equations are used in phenotypic models of selection which examine conditions maximizing the fitness advantage of one phenotype over another with a different sex ratio or allocation. As an example, it is shown that finite population size confers full stability on the sexual allocations in a cosexual population and on the sex ratio in a dioecious population.The use of fitness advantages provides the outcome of selection for all frequencies of contrasted phenotypes. It is therefore possible to redefine an ESS to allow for persistent variability in a population. A phenotype is an ESS in a population if, from any initial frequency, it is protected from loss by its fitness advantage. The conditions for a rare mutant to spread invariably coincide with those for its fixation only if an individual of any phenotype affects the fitness of other individuals of all phenotypes in identical ways.     

Chromosome replacement in mixed populations of compound-2L; free-2R and standard strains of Drosophila melanogaster

Summary Crosses between compound-2L; free-2R (free-arm) and standard strains of Drosophila melanogaster produce two classes of inviable aneuploid hybrids in equal proportions: monosomic 2L and trisomic 2L. The lethal period for monosomics occurs during embryogenesis while the trisomics survive to late pupae. Since the hybrids are inviable, standard and free-arm strains within a mixed population remain genetically isolated. Genetic isolation in the absence of mating isolation offers an extreme example of unstable equilibrium. Relative fitness data indicate that an unstable equilibrium will be established between free-arm and standard strains at a ratio of 2.51. Indeed, in three cage experiments established at initial ratios of 31, free arms to standards, laboratory (Oregon R) or native (Okanagan S) standard strains were completely replaced in approximately 100 days by free-arm lines derived either from laboratory or from native genetic background. In contrast, one cage established at an initial ratio of 41 failed to show replacement and for 92 days remained at approximately the initial ratio. Subsequent genetic analysis of flies removed from this cage identified the presence of an anomalous strain through which genetic information was transferred reciprocally between the free-arm and standard lines. The second chromosomes carried by this strain consisted of a free-2R and a standard second on the right arm of which was attached a duplication for all of 2L. While the origin of the 2L·2R+2L chromosome was uncertain, genetic and cytological examinations revealed that it represented the reciprocal crossover product expected from an exchange that generated a F(2R). Additional crosses disclosed that the transmission frequency of the asymmetrical pair of second chromosomes, as well as their right-arm crossover products, was disproportionately in favor of the short arm. Since unequal transmission was invariably greater from female parents, this phenomenon was viewed as further evidence in support of the drag hypothesis.Supported by research grant A5853 from the National Science and Engineering Research council of Canada to D.G.H.     

Mixed culture of killer and sensitive Saccharomyces cerevisiae strains in batch and continuous fermentations

This paper presents a kinetic study of the dynamics of the population of two Saccharomyces cerevisiae strains (designated K1 and 522D) in mixed culture. These two strains are commonly used in wine making. The K1 strain (killer yeast) secretes a glycoprotein (killer toxin) which causes the death of the 522D strain (sensitive yeast). Initially, the mixed cultures were realized in batch fermentations. Initial concentrations of killer yeast were 5 and 10% of the total population. The influence of the killer strain on the sensitive cultures was measured in comparison with a reference fermentation. The reference fermentation was inoculated only with the sensitive strain. Results show that an initial concentration of 10% of killer strain affects the microbial population balance and the rate of ethanol production. However the fermentation was only slightly disturbed when the proportion of killer to sensitive yeast at the beginning of mixed culture was 5%. To achieve total displacement by the killer yeast at low concentrations, the mixed cultures were carried out in a continuous system. The results obtained in continuous fermentations with the same strains have shown that a level of contamination as low as 0.8% of killer strain was sufficient to completely displace the original sensitive population after 150 h incubation.     

Mixed culture of killer and sensitive Saccharomyces cerevisiae strains in batch and continuous fermentations

This paper presents a kinetic study of the dynamics of the population of two Saccharomyces cerevisiae strains (designated K1 and 522D) in mixed culture. These two strains are commonly used in wine making. The K1 strain (killer yeast) secretes a glycoprotein (killer toxin) which causes the death of the 522D strain (sensitive yeast). Initially, the mixed cultures were realized in batch fermentations. Initial concentrations of killer yeast were 5 and 10% of the total population. The influence of the killer strain on the sensitive cultures was measured in comparison with a reference fermentation. The reference fermentation was inoculated only with the sensitive strain. Results show that an initial concentration of 10% of killer strain affects the microbial population balance and the rate of ethanol production. However the fermentation was only slightly disturbed when the proportion of killer to sensitive yeast at the beginning of mixed culture was 5%. To achieve total displacement by the killer yeast at low concentrations, the mixed cultures were carried out in a continuous system. The results obtained in continuous fermentations with the same strains have shown that a level of contamination as low as 0.8% of killer strain was sufficient to completely displace the original sensitive population after 150 h incubation.     

Fixation of clonal lineages under Muller's ratchet

For clonal lineages of finite size that differ in their deleterious mutational effects, the probability of fixation is investigated by mathematical theory and Monte Carlo simulations. If these fitness effects are sufficiently small in one or both lineages, then the lineage with the less deleterious effects will become fixed with high probability. If, however, in both lineages the deleterious effects are larger than a threshold s(c), then the probability of fixation is independent of the fitness effects and depends only on the initial frequencies of the lineages. This threshold decreases with decreasing genomic mutation rate U and increases with population size N. (For N = 10(5), we have s(c) approximately = 0.1 if U = 1, and s(c) approximately = 0.015 if U = 0.1). Above the threshold, the competition is not driven by the ratio of mean fitnesses of the lineages, but by the relative sizes of the zero-mutation classes, which are independent of the fitness effects of the mutations. After the loss of the zero-mutation class of a lineage, the other lineage will spread to fixation with high probability and within a short time span. If the mutation rates of the lineages differ substantially, the lineage with the lower mutation rate is fixed with very high probability unless the lineage with the larger mutation rate has very slightly deleterious mutational effects. If the mutation rates differ by not more than a few percent, then the lineage with the higher mutation rate and the more deleterious effects can become fixed with appreciable probability for a certain range of parameters. The independence of the fixation probability on the fitness effects in a single population leads to dramatic effects in metapopulations: lineages with more deleterious effects have a much higher fixation probability. The critical value s(c), above which this phenomenon occurs, decreases as the migration rate between the subpopulations decreases.     

Symbiont infection affects whitefly dynamics in the field

Inherited intracellular insect endosymbionts may manipulate host reproduction or provide fitness benefits to their hosts in ways that result in their rapid spread throughout a host population. Fitness benefits in particular can result in the increased pest potential of agriculturally important insects. While benefits due to endosymbiont infection have been well studied in laboratory assays, very little is known about how these benefits translate to insect performance in the field. Laboratory experiments have shown that the maternally inherited bacterial endosymbiont, Rickettsia, increases the fitness of its whitefly host, Bemisia tabaci, through improved fecundity, faster development times and female-biased sex ratios. We conducted field population cage studies to determine whether the benefits conferred by Rickettsia to whiteflies in the laboratory were evident on one of its major hosts, cotton, under field conditions in Arizona, USA. In cages with either Rickettsia-infected or uninfected whiteflies, we observed up to ten-fold higher whitefly egg and nymph densities when whiteflies were Rickettsia-infected compared with uninfected whiteflies throughout the season. We also observed a steep initial increase in Rickettsia frequency in population cages started with either 25% or 50% Rickettsia-infected whiteflies, with the 50% cages approaching fixation within three generations. Using growth rates obtained in the density cages, we calculated and compared an expected trajectory of the frequencies of Rickettsia infection with the observed frequencies. Results showed similar observed and expected frequencies of Rickettsia in the first two generations, followed by a significantly lower than expected frequency in three of four treatment/sample combinations at the end of the season. Taken together, these results confirm the patterns of fecundity and population growth observed in laboratory assays, under field conditions, as well as provides preliminary empirical support for a Rickettsia equilibrium frequency of less than 100%.     

Population dynamics of the 2 major mitochondrial DNA haplotypes in experimental populations of Drosophila subobscura.

The evolution of Drosophila subobscura mitochondrial DNA has been studied in experimental populations, founded with flies from a natural population from Calvià (Majorca, Balearic Islands, Spain). This population, like others founded in Europe, is characterized by the presence of 2 very common (>95%) mitochondrial haplotypes (named I and II) and rare and endemic haplotypes that appear at very low frequencies. Four experimental populations were established with flies having a heterogeneous nuclear genetic background, which was representative of the composition of the natural population. The populations were started with haplotypes I and II at an initial frequency of 50% each. After 33 generations, the 2 haplotypes coexisted. Random drift could be rejected as the only force responsible for the observed changes in haplotype frequencies. A slight but significant linear trend favouring a mtDNA (haploid) fitness effect has been detected, with a nonlinear deviation that could be due to a nuclear component. An analysis of chromosomal arrangements was made before the foundations of the cages and at generation 23. Our results indicated that the hypothesis that the maintenance of the frequencies of haplotypes I and II in natural populations could be due to their association with chromosomal arrangements remains controversial.     

Animal Modelling of Lumbar Corpectomy and Fusion and in vivo Growth of Spine Supporting Bone by Titanium Cage Implants: An Experimental Study

##正## In this study a lumbar spinal fusion animal model is established to assess the effect of spinal fusion cage,and explore theminimum area ratio of titanium cage section to vertebral section that ensures bone healing and biomechanical property.Lumbarcorpectomy was conducted by posterolateral approach with titanium cage implantation combined with plate fixation.Titaniumcages with the same length but different diameters were used.After implantation of titanium cages,the progress of bone healingwas observed and the bone biomechanical properties were measured,including deformation and displacement in axial compression,flexion,extension,and lateral bending motion.The factors affecting the in vivo growth of spine supporting body wereanalyzed.The results show that the area ratio of titanium cage section to vertebral section should reach 1/2 to ensure the bonehealing,sufficient bone intensity and biomechanical properties.Some bone healing indicators,such as BMP,suggest that there isa relationship between the peak time and the peak value of bone formation and metabolism markers and the bone healing strength.     

Modulation of anti-pathogenic activity in canine-derived Lactobacillus species by carbohydrate growth substrate

AIMS: To investigate the effect of various carbon sources on the production of extracellular antagonistic compounds against two Escherichia coli strains and Salmonella enterica serotype Typhimurium by three canine-derived lactobacilli strains. METHODS AND MATERIALS: Cell-free preparations, pH neutralized, were used in antibiotic disc experiments as an initial screening. The bacteria/carbohydrate combinations that showed inhibition of the growth of those pathogens, were further investigated in batch co-culture experiments. The cell-free supernatants of the cultures, that decreased the population number of the pathogens in the co-culture experiments to log CFU ml-1 相似文献   

Measuring fitness by means of balancer chromosomes

We present the theoretical background to a new method for measuring genetic variation for total fitness in Drosophila. The method allows heterozygous effects on total fitness of whole wild-type chromosomes to be measured under normal demography with overlapping generations. The wild-type chromosomes are competed against two balancer chromosomes (B1, B2, say), providing a standard genotype B1/B2 against which variation in the fitness effects of the wild-type chromosomes can be assessed. Fitness can be assessed in two ways: (i) at equilibrium of all three chromosomes under heterozygote advantage, and (ii) during displacement of one balancer by the other. Equilibrium with all three chromosomes present will be achieved only if the wild-type homozygote is not too fit, and if the fitnesses of the three heterozygotes are not too unequal. These conditions were not satisfied for any of a sample of 12 lethal-bearing chromosomes isolated from a random-bred laboratory population of Drosophila. At equilibrium, genotypic frequencies show low sensitivity to changes in genotypic fitness. Furthermore, where all four genotypes are viable and fertile, supplementary information from cages with only two chromosomes present and from direct measurements of pre-adult viability are required to estimate fitnesses from frequencies. The invasion method has the advantages of a greater sensitivity and of not requiring further data to estimate fitnesses if the wild-type homozygote is fertile. However, it requires that multiple samples be taken as the invasion progresses. In a discrete generation model, generation time influences fitness estimates from this method and is difficult to estimate accurately from the data. A full age-structured model can also be applied to the data from both types of experiment. For the invasion method, this gives fitness estimates close to those from the discrete generation model.     

Developing the sterile insect technique for Cryptophlebia leucotreta (Lepidoptera: Tortricidae): influence of radiation dose and release ratio on fruit damage and population growth in field cages

The effect of radiation dose and different release ratios of treated (T) to untreated (U) Cryptophlebia leucotreta (Meyrick) (Lepidoptera: Tortricidae), on the incidence of fruit damage, the competitiveness of the treated males, and population growth was examined inside field cages. Navel orange trees were individually enclosed in large nylon mesh cages. Newly emerged adult moths treated with either 150 or 200 Gy of gamma radiation were released into the cages at ratios of 5T:1U or 10T:1U. The fruit was collected after 4 wk, and the number of damaged fruit and larval entries per cage were recorded for each treatment. Infested fruit was maintained in the laboratory until all emerging F1 progeny were collected and outcrossed to untreated moths of the opposite sex. Treatment had a significant effect on the mean number of larval entries and on the number of undamaged fruit per cage. The number of larval entries as well as the number of F1 progeny per cage decreased as the overflooding ratio increased. A significant reduction in egg hatch was observed in the progeny of crosses between F1 females or F1 males originating from the treatment cages compared with crosses of F1 moths originating from the control cages. The lowest mean number of fertile F1 adult females and males was obtained from the 150 Gy and 10T:1U ratio treatment. This treatment also showed the lowest per generation rate of increase (< 1 from the parental [P1] to the F1 generation), suggesting that growth in the fertile population would have been prevented if releases of treated moths at this dose and ratio were maintained in the field.     

Fitness evolution and the rise of mutator alleles in experimental Escherichia coli populations

We studied the evolution of high mutation rates and the evolution of fitness in three experimental populations of Escherichia coli adapting to a glucose-limited environment. We identified the mutations responsible for the high mutation rates and show that their rate of substitution in all three populations was too rapid to be accounted for simply by genetic drift. In two of the populations, large gains in fitness relative to the ancestor occurred as the mutator alleles rose to fixation, strongly supporting the conclusion that mutator alleles fixed by hitchhiking with beneficial mutations at other loci. In one population, no significant gain in fitness relative to the ancestor occurred in the population as a whole while the mutator allele rose to fixation, but a substantial and significant gain in fitness occurred in the mutator subpopulation as the mutator neared fixation. The spread of the mutator allele from rarity to fixation took >1000 generations in each population. We show that simultaneous adaptive gains in both the mutator and wild-type subpopulations (clonal interference) retarded the mutator fixation in at least one of the populations. We found little evidence that the evolution of high mutation rates accelerated adaptation in these populations.