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PubMed1980

Developmental stability opf Drosophila melanogaster under artificial and natural selection in constant and fluctuating environments.

Populations of Drosophila melanogaster in constant 25 degrees and fluctuating 20/29 degrees environments showed increases in developmental stability, indicated by decreases in bilateral asymmetry of sterno-pleural chaeta number. In both environments, rates of decrease in asymmetry were greater under natural selection (control lines) than under artificial stabilizing selection. Overall mean asymmetry was greater in the fluctuating environment.--There was no evidence that decreased asymmetry was due to heterozygosity, and the decline in asymmetry was not explained by the decline in chaeta number in the lines under natural selection. However, the decline was consistent with changes in total phenotypic variance and environmental variance.--The divergence between lines after 39 generations of selection was seen in differences in asymmetry and also in the genotype-environment interaction expressed in cross-culturing experiments.

Animals↗
PubMed1998

Mutation and conflicts between artificial and natural selection for quantitative traits.

There is substantial new variation for quantitative traits generated by mutation that can be utilised by artificial selection. With long-term selection, however, response is often attenuated and a selection limit sometimes reached, even though genetic variation is frequently still present in these lines. In this paper, the theoretical bases of long-term response and variability of populations that come from mutational variance are reviewed, and the relation between them is related to the strength and mode of the natural selection, whether due to pleiotropic effects of mutant genes or stabilising selection. Simple formulae to predict the consequence of relaxed or reversed selection are derived. Results from long-term selection experiments in mice in this laboratory are described and related to the theoretical analyses with the aim of reconciling the evidence for substantial standing variation with the low rate of response.

Animals↗
PubMed2026

Selection of GhTT2-A07 promoter enhances fiber quality in improved cotton varieties.

Modern cultivated cotton fibers are predominantly white with enhanced quality compared to their wild ancestors. However, the molecular mechanisms and evolutionary drivers linking fiber color to quality remain least focused. In this study, we identified FQC1 (Fiber Quality and Color 1), a major quantitative trait locus (QTL) on chromosome A07 that concurrently regulates both fiber quality and pigmentation. Through map-based cloning, we revealed that Gossypium hirsutum TRANSPARENT TESTA2-A07 (GhTT2-A07), an R2R3-MYB transcription factor, resides within this locus. GhTT2-A07 modulates fiber development by directly activating genes in the general phenylpropanoid pathway, thereby promoting the metabolic flux toward downstream secondary metabolites. Variations in the GhTT2-A07 promoter led to its reduced expression in modern white cotton cultivars. This down-regulation suppresses the accumulation of S/G/H-type lignin monomers and proanthocyanidins, resulting in altered secondary cell wall composition and ultimately enhancing the quality of mature white fibers. Population genetic analyses further indicate that the white-fiber allele GhTT2-A07W has been fixed in modern breeding genotypes, underscoring the impact of artificial selection during cotton domestication. Overall, our study elucidates the biochemical and molecular mechanisms underlying fiber quality and pigmentation in cotton, clarifies the selection criteria for high-quality white fibers in modern cultivars, and provides a theoretical basis for future targeted genetic improvement of cotton fibers.

Alleles↗
PubMed1984

[Direct selection for fertility and health in cattle].

Financial losses in dairy cattle due to breeding inefficiency and health impairment are so high that they should be taken into account in cattle breeding. These disturbances tend to increase as productivity increases. Although these disturbances are quantitative characteristics, they can only be recorded qualitatively. Therefore the heritabilities of breeding inefficiency and health impairment are low. Several of these disturbances (mastitis, metabolic disorders) show a much higher incidence in cows than they do in heifers. Selection for production-traits is mainly based on heifer groups of bulls. Artificial selection designed to prevent disturbances will fail to produce positive results as the heritabilities are low for heifers and the current groups of heifers are too small to obtain a reliable estimate of the breeding value of a bull for disturbances of fertility or health. Natural selection against these disturbances should not be ruled out, and therefore it is advisable to record certain disturbances and to use this recording in the selection of bull dams.

Aging↗
PubMed2003

Correlated evolution of life-history with size at maturity in Daphnia pulicaria: patterns within and between populations.

Explaining the repeated evolution of similar sets of traits under similar environmental conditions is an important issue in evolutionary biology. The extreme alternative classes of explanations for correlated suites of traits are optimal adaptation and genetic constraint resulting from pleiotropy. Adaptive explanations presume that individual traits are free to evolve to their local optima and that convergent evolution represents particularly adaptive combinations of traits. Alternatively, if pleiotropy is strong and difficult to break, strong selection on one or a few particularly important characters would be expected to result in consistent correlated evolution of associated traits. If pleiotropy is common, we predict that the pattern of divergence among populations will consistently reflect the within-population genetic architecture. To test the idea that the multivariate life-history phenotype is largely a byproduct of strong selection on body size, we imposed divergent artificial selection on size at maturity upon two populations of the cladoceran Daphnia pulicaria, chosen on the basis of their extreme divergence in body size. Overall, the trajectory of divergence between the two natural populations did not differ from that predicted by the genetic architecture within each population. However, the pattern of correlated responses suggested the presence of strong pleiotropic constraints only for adult body size and not for other life-history traits. One trait, offspring size, appears to have evolved in a way different from that expected from the within-population genetic architecture and may be under stabilizing selection.

Animals↗
PubMed2005

Contractile abilities of normal and "mini" triceps surae muscles from mice (Mus domesticus) selectively bred for high voluntary wheel running.

As reported previously, artificial selection of house mice caused a 2.7-fold increase in voluntary wheel running of four replicate selected lines compared with four random-bred control lines. Two of the selected lines developed a high incidence of a small-muscle phenotype ("mini muscles") in the plantar flexor group of the hindlimb, which apparently results from a simple Mendelian recessive allele. At generations 36-38, we measured wheel running and key contractile characteristics of soleus and medial gastrocnemius muscles from normal and mini muscles in mice from these selected lines. Mice with mini muscles ran faster and a greater distance per day than normal individuals but not longer. As expected, in mini-muscle mice the medial and lateral gastrocnemius muscles were approximately 54 and 45% the mass of normal muscles, respectively, but the plantaris muscles were not different in mass and soleus muscles were actually 30% larger. In spite of the increased mass, contractile characteristics of the soleus were unchanged in any notable way between mini and normal mice. However, medial gastrocnemius muscles in mini mice were changed markedly toward a slower phenotype, having slower twitches; demonstrated a more curved force-velocity relationship; produced about half the mass-specific isotonic power, 20-50% of the mass-specific cyclic work and power (only 10-25% the absolute power if the loss in mass is considered); and fatigued at about half the rate of normal muscles. These changes would promote increased, aerobically supported running activity but may compromise activities that require high power, such as sprinting.

Animal Husbandry↗
PubMed2003

Responses to selection for cadmium resistance in the least killifish, Heterandria formosa.

An artificial selection experiment was conducted for six generations to investigate the responses to selection for cadmium resistance in the least killifish, Heterandria formosa. There was a rapid response to selection. After only one generation of selection, two of the three selection lines had an increased resistance to cadmium, while all three selection lines had an elevated resistance by the next generation. After six generations of selection, fish from the selection lines survived about three times as long as control line fish when exposed to cadmium. Realized heritability for cadmium resistance was estimated to be 0.50. Cross-resistance to copper was studied in the F2, F3, and F6 generations; fish from the cadmium-resistant lines had a longer survival time than those from the control lines. Resistance to heat was investigated in the F2, F3, and F5 generations; the cadmium-resistant lines had a significantly shorter survival time than the control lines. Our results showed that evolution of resistance to cadmium was rapid, that cross-resistance to copper occurred, and that the evolution of resistance to cadmium was accompanied by a trade-off (fitness costs) as evidenced by the reduced heat tolerance.

Animals↗
PubMed1992

[Changes in the frequency of cells with micronuclei in cell populations of rat transplantable rhabdomyosarcoma RA-2 as a result of selection for an increased and a decreased frequency of such cells].

Artificial selection for increasing and decreasing frequencies of cells with micronuclei (FCM) was conducted in populations of cell clones of the rat transplantable RA-2 rabdomyosarcoma. The selection was effective in both the opposite directions. The average FCM increased from 3.3 +/- 0.2 to 6.9 +/- 0.6% and decreased from 3.3 +/- 0.2 to 1.6 +/- 0.2%. Heritability coefficient, h2, varied from 0.2 to 0.4. In the cell population with increased FCM, 37% of anaphases and early telophases had lagged chromosomes and fragments. In contrast, in the cell population with decreased FCM, lagging were observed in 11% of cases. The DNA-content in G1 cell varied greatly in cell population with increased FCM (P < 0.01). The selection for increased FCM has led to a significant decrease in metastatic capacities of cells.

Animals↗
PubMedDate not supplied

[The noradrenaline content and the alpha 2-adrenoreceptor count in the brain of brown rats selected for the absence of aggressive behavior in relation to man].

Artificial selection of gray rats by the domestic type of behaviour resulted in an increase of the noradrenaline content, but in a decrease of the alpha 2-adrenergic receptors number in the hypothalamus. The data suggest a significant difference in noradrenergic system between domesticated and aggressive animals associated with changes in aggressive behaviour towards man during selection.

Aggression↗
PubMed1998

Adult fitness consequences of sexual selection in Drosophila melanogaster.

Few experiments have demonstrated a genetic correlation between the process of sexual selection and fitness benefits in offspring, either through female choice or male competition. Those that have looked at the relationship between female choice and offspring fitness have focused on juvenile fitness components, rather than fitness at later stages in the life cycle. In addition, many of these studies have not controlled for possible maternal effects. To test for a relationship between sexual selection and adult fitness, we carried out an artificial selection experiment in the fruit fly, Drosophila melanogaster. We created two treatments that varied in the level of opportunity for sexual selection. Increased opportunity for female choice and male competition was genetically correlated with an increase in adult survivorship, as well as an increase in male and female body size. Contrary to previous, single-generation studies, we did not find an increase in larval competitive ability. This study demonstrates that mate choice and/or male-male competition are correlated with an increase in at least one adult fitness component of offspring.

Aging↗
PubMed1983

Breeding for immune responsiveness and disease resistance.

Animal production efficiency, and product volume and quality can be greatly increased by reducing disease losses. Genetic variation, a prerequisite for successful selection, has been found in animals and poultry exposed to a variety of viral, bacterial and parasitic infections. Breeding for disease resistance can play a significant role alone or in combination with other control measures including disease eradication, vaccination and medication. Feasibility of simultaneously improving resistance to specific diseases and production traits has been demonstrated. However, selection for specific resistance to all diseases of animals and poultry is impossible. Development of general disease resistance through indirect selection primarily on immune response traits may be the best long-term strategy but its applicability is presently limited by insufficient understanding of resistance mechanisms. Another hindrance may be negative genetic correlations among various immune response functions: phagocytosis, cell mediated and humoral immunity. To better assess the feasibility of increasing general disease resistance by indirect selection we must obtain estimates of heritability for immune response, disease resistance, and economic production traits, as well as genetic correlations among these traits. The present level of disease resistance in farm animals resulted from natural selection and from correlated responses to selection for production traits while the influence of artificial selection for resistance was minimal. Future research should be directed towards developing and applying breeding techniques that will increase resistance to diseases without compromising production efficiency and product quality. This will require cooperation of immunogeneticists, veterinarians and animal and poultry breeders. Significant progress in the improvement of resistance to diseases may result from the application of new techniques of molecular genetics and cell manipulation.

Animal Diseases↗
PubMed1997

[Effect of domestication of the silver fox on the main enzymes of serotonin metabolism and serotonin receptors].

In silver foxes significant alterations in the activities of basic enzymes of neurotransmitter serotonin metabolism as well as in the densities of receptors caused by selection for the absence of the aggressive defensive reaction to man were demonstrated. In the midbrain and hypothalamus of animals selected for the absence of aggressive behavior, the activity of tryptophan hydroxylase, the key enzyme of serotonin biosynthesis, was found to be remarkably higher than in animals selected for highly aggressive behavior. Domesticated animals were characterized by low activity of the main enzyme of serotonin catabolism, monoamine oxidase type A, increased Michaelis constant km, and an unchanged maximum reaction rate (Vmax). No changes in the specific binding of [3H]-ketanserin and [3H]-8-OH-DPAT in the frontal cortex of domesticated foxes were revealed; however, in the hypothalamus, the low values of Bmax for the [3H]-8-OH-DPAT specific binding were observed, indicating the decreased density of the 5-HT1A receptors. It is assumed that the transformation of a wild aggressive animal into a domesticated one taking place during directional selection is caused by hereditary alterations favored by artificial selection in the activity of the main enzymes of serotonin metabolism and serotonin receptors.

Aggression↗
PubMed1997

In vitro characterization of lines of Oesophagostomum dentatum selected or not selected for resistance to pyrantel, levamisole and ivermectin.

Lines of Oesophagostomum dentatum artificially selected or not selected for resistance to pyrantel, levamisole and ivermectin were used in this study. From the 10th generation of selection eggs were collected from each line and subjected to an in vitro larval development assay (LDA) and an egg hatch assay (EHPA). Significant differences were observed between an unselected line of O. dentatum and the lines selected for resistance to levamisole or pyrantel in both assays. The LDA was more sensitive than EHPA in detecting anthelmintic resistance in O. dentatum. The results obtained from the LDA confirmed side-resistance between levamisole and morantel/pyrantel. The in vitro tests failed to show significant differences between ivermectin-sensitive and resistant lines.

Animals↗
PubMed2000

Behavioral profiles of genetically selected aggressive and nonaggressive male wild house mice in two anxiety tests.

Artificially selected aggressive (SAL) and non-aggressive (LAL) male house mice were tested in a hexagonal tunnel maze and light-dark preference (LD) box to determine if the bidirectional selection for aggressive behavior leads to a coselection for different levels of trait anxiety. The tunnel maze consists of an open, brightly lit central arena surrounded by a complex system of interconnecting tunnels. As in the LD box, animals which spend less time and are less active in the brightly illuminated section of the maze are considered to have higher anxiety levels. In the tunnel maze, the LAL mice showed more exploration and spent more time in the central arena than the SAL animals, but only during the final 2 min of the 6-min test. This reduced preference for the central arena was not due to general inactivity or a failure of the SAL to find the central arena and indicates a higher level of state anxiety in the aggressive animals. In contrast, no "anxiety-like" differences were found in the LD box, either for the percentage of time spent in the light compartment or for the number of crossings. SAL males actually showed higher levels of moving and rearing, and lower levels of freezing, than did LAL males.

Aggression↗
PubMed1975

Changes in relative aggressiveness and social dominance associated with selection for early egg production in chickens.

We tested the hypothesis that artificial selection for early reproductive performance of chickens kept under competitive conditions increases aggressiveness and social dominance. Two populations subjected to long-term selection for number of eggs laid before 40 weeks of age and the unselected control population from which they derived were used. Results generally supported the hypothesis but indicated that increased aggressiveness associated with such selection may characterize the adolescent period only. For one of the selected strains, rank for aggressiveness and social dominance between adolescence and full maturity was reversed, relative to the control population. Associations between increased aggressiveness (and social dominance) and decreased age at sexual maturity are discussed, along with implications as to the role of social status and reproductive performance when different genetic strains compete within flocks.

Aggression↗
PubMed1977

Some population genetic models combining artificial and natural selection pressures in the presence of assortative mating.

We have attempted quantitatively through a series of assortative mating models to gain insight into the interaction between the usually antagonistic tendencies of artifical and natural selection pressures. We summarize some of the robust conclusions. In cases where natural selection is expressed only through the phenotype and acts in the opposite direction to the culling incline, then fixation of the dominant or recessive type can be achieved and which occurs depends critically on the initial composition of the population and the magnitude of the degree of culling compared to the selection coefficients. With traits determined at two loci in the case that the double heterozygote is the desired kind, the effect of selfing can only be overcome by very strong artificial selection pressures (high culling order). The degree of culling to achieve its objective can be relaxed with weakening of linkage. The relevant comparison is r2+(1-r)2less than 2(1-c) indicating the precise extent of culling needed, to prevent fixation. The relationships are more complex when natural selection forces are also involved (see Model IV).

Alleles↗
PubMed1983

Effects of genotype and maternal alcohol consumption on some biochemical parameters of red blood cells in the progeny of mice.

Effects of genotype and ethanol consumption by pregnant mothers on hemoglobin (Hb) and red-cell levels of adenosine triphosphate (ATP), 2,3-diphosphoglycerate (DPG), and glutathione (GSH) of their progeny were studied in mice. Three lines of mice were used, one selected for high body weight, another selected for low body weight, and an unselected control. An ethanol solution [10% (v/v)] was given ad lib to the females at the time of joining them with males and continued through the pregnancy. Another group received distilled water for drinking throughout. Blood samples from the progeny of both these groups were taken at 10 weeks of age and analyzed for Hb, ATP, DPG, and GSH levels. Alcohol drinking during pregnancy resulted in lower levels of DPG in the red blood cells of progeny of the lines selected for high and low body weight and the reverse in the unselected line. Maternal alcohol consumption had no effect on Hb, APT, and GSH levels in the red blood cells of the progeny of any of the three lines. Females of both selected lines had higher levels of DPG than males. Artificial selection for body weight resulted in a positively correlated response in the level of red-cell DPG and GSH in the progeny.

Adenosine Triphosphate↗
PubMed1991

Quantitative genetics of postponed aging in Drosophila melanogaster. II. Analysis of selected lines.

Quantitative genetic analyses of Drosophila melanogaster stocks with postponed aging have suffered from the problem of a lack of certainty concerning patterns of allelic differentiation. The present experiments were designed to alleviate this difficulty by selecting for enhanced levels of characters known to be related to postponed aging. Selection successfully increased the degree of differentiation of postponed aging stocks with respect to starvation resistance and fecundity, but persistent additive genetic variance suggested that selection did not result in fixation of alleles. The artificially selected stocks were subjected to crosses to test for patterns of dominance and maternal effects. There was little evidence for these effects in the inheritance of the characters underlying postponed aging, even with the increased differentiation of the selected stocks.

Aging↗