Selection response for part period egg number and egg mass in chickens — a comparison

Summary Two sublines from each of four flocks of White Leghorn were subjected to two cycles of selection for part year egg number and part year egg mass. A family index (combined selection) was the selection criterion for each of the two traits. The generation means of an unselected pedigreed randombred control, bred and maintained along with the selected sub-lines, were used for correcting short term environmental trends. The sublines selected for a common selection criterion were considered as replicates. The control corrected generation means, when averaged over replicates, gave the mean direct and correlated responses for the selected and different unselected traits. The average genetic change per generation was 2.16 eggs in egg number selected sublines and 146 g of egg mass in egg mass selected sublines. The direct response marginally exceeded the correlated response for both part period egg number and egg mass seen in the corresponding sublines. Except for egg weight the correlated responses for different unselected traits were in the same direction in both egg number and egg mass selected sublines. While the egg weight in egg number lines did not change, its response was positive in egg mass selected lines. A comparison between the lines revealed that the egg mass selected lines matured later and laid heavier but slightly less numerous eggs than the egg number selected sub-lines.     

Correlated effects of the response to conditioned medium in the flour beetle,Tribolium castaneum

Dispersal rates were measured in lines selected for high and low response of egg production to conditioned media, and responsivness of egg production was measured in lines selected for high and low dispersal. A positive correlation was found between these two traits, each of which had previously been found to have a simple genetic basis. It is suggested that in Tribolium castaneum the sensitivity to environmental conditions is mediated through a Sensor gene, which can activate either response, according to circumstances.     

The use of genetic markers to measure genomic response to selection in livestock

A method to measure genomic response to natural and artificial selection by means of genetic markers in livestock is proposed. Genomic response through several levels of selection was measured using sequential testing for distorted segregation of alleles among selected and nonselected sons, single-sperm typing, and a test with records for growth performance. Statistical power at a significance level of 0.05 was >0.5 for a marker linked to a QTL with recombination fractions 0, 0.10, and 0.20 for detecting genomic responses for gene effects of 0.6, 0.7, and 1.0 phenotypic standard deviations, respectively. Genomic response to artificial selection in six commercial bull sire families comprising 285 half-sib sons selected for growth performance was measured using 282 genetic markers evenly distributed over the cattle genome. A genome-wide test using selected sons was significant (P < 0.001), indicating that selection induces changes in the genetic makeup of commercial cattle populations. Markers located in chromosomes 6, 10, and 16 identified regions in those chromosomes that are changing due to artificial selection as revealed by the association of records of performance with alleles at specific markers. Either natural selection or genetic drift may cause the observed genomic response for markers in chromosomes 1, 7, and 17.     

Population selection to maximize value in an environmental gradient

Summary A theory for determining optimum planting and breeding zones is described. The theory is based on a model consisting of Gaussian response functions for traits that vary in a gradient for a single environmental variable. Environments are assumed to be normally distributed with known mean and variance. Methods are presented for determining parameters of response functions that maximize the expected value for such a trait when two, three and four populations are selected for breeding or as sources of propagules. Expected value is maximized only when the populations selected have response functions symmetrically arrayed about the mean of the environmental variable. Maximum expected value was shown to increase with increasing number of selected populations at a rate that depends upon the ratio of homostasis to environmental variability. The methods presented are illustrated with data on performance of Scots pine provenances in Sweden.Paper No. 11750 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695-7601     

Sporophytic response to pollen selection for Alachlor tolerance in maize

In order to assess the efficiency of male gametophytic selection (MGS) for crop improvement, pollen selection for tolerance to herbicide was applied in maize. The experiment was designed to test the parallel reactivity to Alachlor of pollen and plants grown in controlled conditions or in the field, the response to pollen selection in the sporophytic progeny, the response to a second cycle of MGS, and the transmission of the selected trait to the following generations. The results demonstrated that pollen assay can be used to predict Alachlor tolerance under field conditions and to monitor the response to selection. A positive response to selection applied to pollen in the sporophytic progeny was obtained in diverse genetic backgrounds, indicating that the technique can be generally included in standard breeding programs; the analysis of the data produced in a second selection cycle indicated that the selected trait is maintained in the next generation.     

Cyclic adenosine-3',5'-monophosphate alters hydrolysis of phospholipids by mouse embryo palate mesenchyme cells

The purpose of this study was to determine whether inhibition of release of arachidonic acid from mouse embryo palate mesenchyme (MEPM) cells in response to cAMP is due to a selected or generalized inhibition of hydrolysis of esterified pools of arachidonic acid. The calcium ionophore A23187 proved to be a useful probe of phospholipid hydrolases in MEPM cells, since it stimulated release of radiolabeled fatty acids from phospholipids of prelabeled MEPM cells as a function of the length of exposure, concentration, and concentration of Ca2+ in the medium. Elevation of intracellular levels of cAMP by treatment with (-) isoproterenol resulted in the inhibition of release of radiolabeled arachidonic acid in response to A23187. Analysis by quantitative gas-liquid chromatography revealed the source of the arachidonic acid released in response to the ionophore to be 1,2-diradyl-sn-glycero-3-phosphoethanolamine; elevation of intracellular levels of cAMP inhibited hydrolysis of this substrate, but may have stimulated hydrolysis of 1,2-diradyl-sn-glycero-3-phosphocholine. These findings permit the conclusions that 1) the ionophore stimulates activities of selected phospholipases A in MEPM cells and 2) cAMP modulates certain phospholipases A in MEPM cells in a specific manner.     

Direct and correlated responses to artificial selection on lipid and glycogen contents in Drosophila melanogaster

A large outbred population of Drosophila melanogaster was subjected to artificial selection on lipid and glycogen storage. In three separate experiments, two replicates underwent sib selection for both increased and decreased storage. In the first study, flies were selected on the basis of total triacylglycerol for ten generations. This experiment resulted in no significant direct response, but there was a significant change in total body weight, underscoring the importance of concern for the allometric relationship between body weight and lipid content. In the second study, selection was performed for 15 generations on the percentage of body composition that was triacylglycerol. A significant direct response was obtained, and the two replicates revealed heritability estimates of 0.40 and 0.43. The third study selected glycogen content for 15 generations, and produced a significant response with heritabilities of 0.25 and 0.31. A series of 12 biochemical and enzyme kinetic traits was examined at five generation intervals in all experiments, and a number of correlated responses were detected. The results are interpreted with respect to the evolutionary constraints on energy storage evolution and the genetic basis of the allometric relationship between body weight and fat content.     

Evolution of starvation resistance in Drosophila melanogaster: measurement of direct and correlated responses to artificial selection

Laboratory selection for resistance to starvation has been conducted under relatively controlled conditions to investigate direct and correlated responses to artificial selection. With regard to starvation resistance, there are three physiological routes by which the trait can evolve: resource accumulation, energy conservation and starvation tolerance. A majority of energetic compounds and macromolecules including triglycerides, trehalose and other sugars, and soluble protein increased in abundance as a result of selection. Movement was additionally investigated with selected males moving less than control males and selected females exhibiting a similar response to selection. Results obtained from this study supported two of the possible evolutionary mechanisms for adaptation to starvation: energy compound storage and conservation. If the response to selection is based on an evolutionarily conserved pattern of genetic correlations (elevated lipid, elevated sugars and reduced movement), then the response to selection is medically relevant and the genetic architecture should be investigated in depth.     

Responses of mouse spinal neurones in culture to locally applied Phe-Met-Arg-Phe-NH2

Embryonic mouse spinal cord neurones were maintained in a primary dissociated culture with a medium free from antibiotics. Intracellular recordings were made and the effects of local application of the neuropeptide FMRFamide were tested on selected neurones. Two types of response were seen. One response was depolarizing, with an accompanying decrease in conductance. This response was probably caused by a reduction in permeability to potassium ions. The second type of response was accompanied by an increase in conductance. Such responses showed a wide variation in their reversal potentials between different neurones. A combination of permeability changes to sodium and chloride ions appeared to be responsible for these responses.     

High-resolution mapping of the human T-cell leukemia virus type 1 Rex-binding element by in vitro selection.

Interactions between the Rex protein of HTLV-1 and the genomic Rex-binding element (XBE) mediate the cytoplasmic transport of viral mRNAs. However, it is uncertain which RNA sequences and structures contribute to Rex recognition. A portion of the viral genome that spanned the XBE was partially randomized, and functional Rex-binding variants were selected. Alignment of selected Rex-binding sequences revealed positions that were functionally conserved between different molecules. A model is presented in which a subset of the selected residues are in direct contact with Rex. Positions that covaried with one another were also found. These covariations support a secondary-structural model in which a central paired stem is symmetrically flanked by two bulge loops. On the basis of this model, site-directed mutations of the XBE were constructed and each half molecule was found to bind independently to Rex. The functional residues and secondary structures in the XBE half molecules bear a remarkable resemblance to the transactivation response region element of HIV-1. Since the transactivation response region element is known to interact specifically with arginine residues in the Tat protein, these results suggest that the XBE binds to the arginine-rich RNA-binding domain of Rex in a similar manner. This model is supported by the selection data.     

Transient response method for evaluating the rate constants of reactions over immobilized enzymes

The transient response method was utilized to evaluate the rate constants of reaction over immobilized enzyme. Glucose oxidation catalyzed by the immobilized glucose oxidase in a fixed-bed reactor was selected as an example. A theoretical model including the effects of axial dispersion, film diffusion, and intraparticle diffusion was established for the reactor. The individual rate constant of each elementary step of this enzymatic reaction was determined through direct fitting of the experimental response data to the model.     

Asymmetrical responses to automatic selection for body size in Drosophila melanogaster

Summary An apparatus has been made for the automatic selection of Drosophila for body size, operating on the principle of a fractionating sieve. The measurements of individual flies by this method were approximately normally distributed and the repeatability of measurements on successive days was 0.5. A two-way selection experiment for this character was carried out with two replicates for ten generations. The realised heritability for the measured score was 0.14±0.02 for high score and 0.20±0.02 when it was for low score. The correlated response in body weight was asymmetrical, the change downwards being much greater than that upwards. There was a clear divergence in activity measurements between the lines selected in the two directions but no clear trends in fertility. Examination of the selected lines after eleven generations showed that the relationship between score and body weight was clearly different in the lines selected in the two directions and was non-linear in both.It is suggested that the response in activity observed as a consequence of selection for score is partly due to the direct response for activity and partly to a correlated response because of a negative genetic correlation between body size and activity. The observed non-linear relationship between score and body weight observed within generations may be a direct cause of the asymmetry of direct and correlated responses which may also have a parallel in other situations.     

THE RESPONSE TO SELECTION FOR FAST LARVAL DEVELOPMENT IN DROSOPHILA MELANOGASTER AND ITS EFFECT ON ADULT WEIGHT: AN EXAMPLE OF A FITNESS TRADE-OFF

A selection experiment using Drosophila melanogaster revealed a strong trade-off between adult weight and larval development time (LDT), supporting the view that antagonistic pleiotropy for these two fitness traits determines mean adult size. Two experimental lines of flies were selected for a shorter LDT (measured from egg laying to pupation). After 15 generations LDT was reduced by an average of 7.9%. The response appeared to be controlled primarily by autosomal loci. A correlated response to the selection was a reduction in adult dry weight: individuals from the selected populations were on average 15.1% lighter than the controls. The lighter females of the selected lines showed a 35% drop in fecundity, but no change in longevity. Thus, there is no direct relationship between LDT and adult longevity. The genetic correlation between weight and LDT, as measured from their joint response to selection, was 0.86. Although there was weak evidence for dominance in LDT, there was none for weight, making it unlikely that selection acting on this antagonistic pleiotropy could lead to a stable polymorphism. In all lines, sex differences in weight violated expectations based on intrasex genetic correlations: Females, being larger than males, ought to require a longer LDT, whereas there was a slight trend in the opposite direction. Because the sexual dimorphism in size was not significantly altered by selection, it appears that the controlling loci are either invariant or have very limited pleiotropic effect on developmental time. It is suggested that they probably control some intrinsic, energy-intensive developmental process in males.     

An empirical comparison of selection methods for the improvement of biomass

Summary A single generation of upward truncation selection on families with 20% selected was carried out in each of five replicates using Tribolium castaneum as the test organism. The experiment involved eight lines: N — selected for offspring number; W — selected for pupal weight; B — selected for biomass; Q — quadratic index selected; L₂₁ — linear index selected with relative economic weights of 21 offspring number to pupal weight; L₁₁ — linear index selected with relative economic weights of 11 offspring number to pupal weight; L₁₂ — linear index selected with relative economic weights of 12 offspring number to pupal weight; C — an unselected control.Biomass (weight of offspring per family), offspring number, and pupal weight were measured. No differences in response to selection were found among the linear index lines and the pupal weight line with regard to any trait analysed. Generally, response to selection in the linear index lines and pupal weight line was small for offspring number and high for pupal weight. Selection pressure on offspring number in these lines seemed to be dependent on the correlation between offspring number and pupal weight. As a result, response to selection for biomass was poor in the linear index and pupal weight selected lines. In the case of the linear indices, poor response to selection for biomass appeared to be due to the violation of the assumption of additivity of the traits included in the definition of aggregate genotype.The responses in the quadratic index, biomass, and offspring number selected lines were equal with respect to selection for biomass. The response of the quadratic index selected line was less than the responses of the biomass and offspring number selected lines for offspring number, but the response in the quadratic index line was as large as that of any other line included in the experiment and greater than the biomass and offspring number selected lines where pupal weight was the criterion.Highly significant amounts of variation were found for all traits indicating that more replicates are needed for precise evaluation of selection systems.     

Genomic regions associated with antibody response to sheep red blood cells in the chicken

F(1) and F(2) populations were generated by crossing two lines of chickens divergently selected from a common founder population for 32 generations for either high or low antibody response 5 days post-injection of a non-pathogenic antigen, sheep red blood cells (SRBCs). The number of loci with major effects on day 5 SRBC titers was estimated to be more than 7 in this population. There was a significant association between MHC haplotype and day 5 antibody titers as well as body weight at sexual maturity. A significant difference between reciprocal F(2) crosses for both 5- and 12-day antibody titers suggests that sex chromosome and/or parent of origin effects on autosomal loci have an important role in immune response. A single marker-trait association analysis on 1024 genetic markers and 128 F(2) individuals detected 11 genomic regions associated with antibody response traits and 17 regions associated with body weight gain. Several of the genomic regions identified as being associated with antibody response have been described previously, while novel regions associated with antibody response were identified on chromosomes 11 and 24. Based on the lack of overlap of the regions associated with body weight and antibody response, we conclude that while these phenotypes are inversely correlated in the selected lines, they are controlled by distinct genetic loci and may be reflective of intense selection pressure on loci affecting the partitioning of nutrients between the immune system and growth pathways.     

Increased Selection Response in Larger Populations. II. Selection for Ethanol Vapor Resistance in Drosophila Melanogaster at Two Population Sizes

The effect of large population size on selection response was investigated using Drosophila melanogaster, with four "small" lines of 160 selected parents/generation compared to two "large" lines of 1,600 selected parents/generation. All lines were selected under similar conditions at a selection intensity of approximately 0.55 standard deviations, for 65 generations, for increased ethanol vapor resistance (measured in minutes required to become anesthetized). Two unselected control lines of 320 parents/generation were also maintained. A significant effect of population size was found. The final treatment means and standard errors were: 27.91 +/- 1.28 min (two "large" lines); 19.40 +/- 1.54 min (four "small" lines); and 4.98 +/- 0.35 min (two control lines). To estimate the mutation rate for the trait, two isogenic lines of about 400 selected parents were selected for 29 generations. The mean increase in additive genetic variance per generation was 0.0009 times the initial environmental variance of the outbred lines. This is comparable to other reported mutation rates. Mutation can explain part of the difference in evolved resistance between treatments, but it appears that even at rather large population sizes, a large difference in long-term response can be obtained in larger outbred lines, from more complete utilization of the initial genetic variation.     

Antigenic properties of peptidic mimics for epitopes of the lipopolysaccharide from Brucella.

The lipopolysaccharide (LPS) is up to now the only identified major virulence determinant of Brucella. This bacterium is responsible for brucellosis in animals and for Malta fever in humans. Several monoclonal antibodies (mAbs) directed against various LPS epitopes have been characterized. Two mAbs, named A15-6B3 and B66-2C8, directed against distinct LPS epitopes have been used to select peptides from 11 phage display libraries. The sequences of the selected peptides contain an overrepresentation of either proline or tryptophan residues when selected with either A15-6B3 or B66-2C8 mAbs, respectively. For the best binding peptides, competition with LPS for the binding to the mAb is detected, which suggests that the peptides bind to the paratope of the mAb. The phages selected from the libraries were used to immunise mice, and a weak antibody response directed against LPS has been observed. These data suggest that a subset of the selected peptides are mimotopes of the LPS epitopes.     

Survival and immune response of drones of a Nosemosis tolerant honey bee strain towards N. ceranae infections

Honey bee colonies (Apis mellifera) have been selected for low level of Nosema in Denmark over decades and Nosema is now rarely found in bee colonies from these breeding lines. We compared the immune response of a selected and an unselected honey bee lineage, taking advantage of the haploid males to study its potential impact on the tolerance toward Nosema ceranae, a novel introduced microsporidian pathogen. After artificial infections of the N. ceranae spores, the lineage selected for Nosema tolerance showed a higher N. ceranae spore load, a lower mortality and an up-regulated immune response. The differences in the response of the innate immune system between the selected and unselected lineage were strongest at day six post infection. In particular genes of the Toll pathway were up-regulated in the selected strain, probably is the main immune pathway involved in N. ceranae infection response. After decades of selective breeding for Nosema tolerance in the Danish strain, it appears these bees are tolerant to N. ceranae infections.     

Reduced learning ability as a consequence of evolutionary adaptation to nutritional stress in Drosophila melanogaster

Abstract 1. Dietary conditions affect cognitive abilities of many species, but it is unclear to what extent this physiological effect translates into an evolutionary relationship. 2. A reduction of competitive ability under nutritional stress has been reported as a correlated response to selection for learning ability in Drosophila melanogaster. Here we test whether the reverse holds as well, i.e. whether an evolutionary adaptation to poor food conditions leads to a decrease in learning capacities. 3. Populations of D. melanogaster were: (i) not subject to selection (control), (ii) selected for improved learning ability, (iii) selected for survival and fast development on poor food, or (iv) subject to both selection regimes. 4. There was no detectable response to selection for learning ability. 5. Selection on poor food led to higher survival, faster development and smaller adult size as a direct response, and to reduced learning ability as a correlated response. This study supports the hypothesis that adaptation to poor nutrition is likely to trade off with the evolution of improved learning ability.     

Effect of bacterial pyrogen on three lizard species

1. Three lizard species (Callopistes maculatus, Gerrhosaurus major, and Varanus exanthematicus) were tested for their response to intraperitoneal injection of alcohol-killed Aeromonas sobria. 2. A paired experimental design, in which each animal received an injection of sterile saline and 1 x 10(10) A. sobria, was utilized. 3. C. maculatus demonstrated a statistically significant increase in mean selected body temperature (MSBT) after bacteria injection. 4. G. major and V. exanthematicus did not demonstrate a statistically significant increase in MSBT. 5. C. maculatus is the first lizard species outside of the family Iguanidae to exhibit a febrile response to bacterial pyrogen.