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Results for “artificial selection”

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PubMed1990

Nonspecific imprintability of quail to colors: response to artificial selection.

Eleven generations of bidirectionally selecting quail (C. coturnix japonica) for nonspecific imprintability to blue or red stimuli resulted in unexpectedly slow yet reliable differentiation of "Hi" and "Lo" imprintability lines. Correlated changes were observed in the variances of unconditional color choices in subjects belonging to these genetic lines. Implications of the data for understanding the interrelated expression of gene effects and environment effects in the development of behavior are discussed.

Animals↗
PubMed2006

Artificial selection for increased maternal defense behavior in mice.

Maternal aggression is directed towards intruders by lactating females and is critical for defense of offspring. Within-family selection for increased maternal defense in outbred house mice (Mus domesticus; Hsd:ICR strain) was applied to one selected (S) line, using total duration of attacks in a 3-min test as the selection criterion. One control (C) line was maintained and both lines were propagated by 13 families in each generation. Prior to selection, heritability of maternal aggression was estimated to be 0.61 based on mother-offspring regression. Duration of attacks responded to selection with a mean realized heritability of 0.40 (corrected for within-family selection) after eight generations. At generation 5, the S and C line also differed significantly for litter size at birth and at mid-lactation (both lower in S), average individual pup mass at midlactation (higher in S), and pup retrieval latency (longer in S), but not for other maternal measures that we studied (e.g., dam mass). Additionally, number of entries to middle and closed plus maze compartments was significantly higher in S mice in Generation 5. This is the first study to select for high maternal defense and these mice will be made available as a tool for understanding the genetic and neural basis of maternal aggression.

Aggression↗
PubMed1987

Genotypic distribution at the limits to natural and artificial selection with mutation.

A general procedure for analysing the change of genotypic distributions under stabilizing and truncation selection is described here and used to investigate the genotypic distribution at the limits to selection. For comparison, a simple approximate procedure using a normal distribution is also presented. It is clear that in the long term truncation introduces departures from normality mainly through gene frequency change, rather than through the generation of linkage disequilibrium under random mating. The Gaussian approximation performs reasonably well for additive gene effects unless the mean gene frequency is very extreme (say, outside the range of 0.05 to 0.95) and the number of loci is small (say, less then 50) regardless of the type of selection in operation. The genotypic distribution at the limits to selection largely depends on the type of limit reached. If a limit is obtained due to the action of natural selection before the exhaustion of existing variation, the distribution will normally not be very skew, but if a limit is reached at which mutation plays a central role in the maintenance of genetic variability, it could have high coefficients of skewness and kurtosis. The role of mutation on the long-term response is also discussed.

Gene Frequency↗
PubMed1990

Long-term response to artificial selection with multiple alleles--study by simulations.

The effect of multiple alleles on long-term response to selection is examined by simulations using a pseudosampling technique to simulate the multidimensional diffusion process. The effects of alleles are independently drawn from a normal distribution and the initial frequencies of alleles are assumed either to be equal or to be drawn from a neutral equilibrium population. With these two initial gene frequency distributions we examined various properties of the selection response process for the effects of number of alleles and selection intensity. For neutral initial frequencies the effects of multiple alleles compared with two alleles are minor on the ratio of final to initial response (E(R infinity/E(R1)) and the half life of response (t0.5), but are significant on the variance of response. Under certain conditions the variance of the selection limit can even increase as selection gets stronger. For equal initial frequencies the effects of multiple alleles are, however, minor on the ratio of the variance of the selection limit to the initial genetic variance, but E(R infinity/E(R1) and t0.5 increase as the number of alleles increases. The results show that for certain statistics the effects of multiple alleles can be minimized by an appropriate transformation of parameters for given initial gene frequencies, but the effects cannot, in general, be removed by any single transformation or reparameterization of parameters.

Alleles↗
PubMed2002

Dominance, plasma testosterone levels, and testis size in house mice artificially selected for high activity levels.

Male house mice (Mus domesticus) from four replicate lines selectively bred for high voluntary wheel-running behavior were compared with four random-bred control lines with respect to dominance, testis size, and plasma testosterone level. Behavior was measured with a tube apparatus in which focal mice encountered a standard opponent from an inbred strain, and positions of mice were scored over a 10-min period; the test was replicated the following day. Blood samples were taken from undisturbed mice 1 week prior to testing (baseline condition) and immediately after the first tube test; plasma testosterone was measured by enzyme immunoassay with chromatography. As compared with control lines, mice from selected lines tended to be smaller in body mass, to have larger testes, and were significantly less likely to advance towards their opponent during the second tube-test encounter. However, no significant differences in either baseline or post-encounter testosterone levels were detected. Significant differences in body mass, relative testis size, position during the first tube-test encounter, and baseline testosterone were found among the replicate lines within linetype, which indicates founder effects, random genetic drift, unique mutations, and/or multiple responses to selection. At the level of individual variation (residuals from nested analysis of covariance models), an inverse relationship between baseline testosterone and advancing in the tube test was observed, and the relationship was stronger during the second test day. This unexpected result may reflect an alternate coping strategy.

Animals↗
PubMed1991

Behavioural differences between artificially selected aggressive and non-aggressive mice: response to apomorphine.

The present study reports a first attempt to unravel the neurochemical background that underlies the difference in behavioural profiles between aggressive and non-aggressive male mice. For this purpose two bidirectionally selected lines for attack latency (SAL and LAL) were used. In pursuit of Cools'9 approach, the susceptibility of individuals of both selection lines to the dopamine agonist apomorphine was measured. The apomorphine was injected subcutaneously at dose levels of 2.5 and 5.0 mg/kg. Apomorphine is considered to stimulate the dopamine receptors in the telencephalon and induces stereotyped behaviour. The responsivity to apomorphine can be rated as a total stereotypy-score. SAL (aggressive) mice showed a significantly greater enhancement of stereotyped behaviour in response to apomorphine than LAL (non-aggressive) mice. In addition, it was demonstrated that this difference is of a quantitative rather than qualitative character. Pharmacokinetic variation between the two lines could be ruled out as cause of the difference. Hence, it was concluded that SAL mice are more sensitive to apomorphine than LAL males, which provides evidence for a difference in the dopaminergic system between the two selection lines. It was suggested that this difference underlies the difference in flexibility in behaviour between aggressive and non-aggressive male mice.

Aggression↗
PubMed1998

Immunological confirmation of elevated levels of CuZn superoxide dismutase protein in an artificially selected long-lived strain of Drosophila melanogaster.

Oxidative stress-induced damage is a major causal factor leading to the loss of function characteristic of the aging process. Various antioxidant defenses are marshalled by the organism so as to combat this oxidative damage and delay the onset of senscence. CuZnSOD is one of the major antioxidant enzymes and has been shown to play an important role in the extended longevity of Drosophila melanogaster. Although assays exist with which to measure the CuZnSOD RNA prevalence and enzyme activity, there existed no antibodies that permitted the measurement of the actual amount of Drosophila enzyme protein present. Development of such a tool would enhance our ability to understand mechanisms of antioxidant gene expression in this organism. We have developed a polyclonal antibody against synthetic SOD peptides that is specific for Drosophila CuZnSOD as shown by Western blots. It is very sensitive when tested against native Drosophila CuZnSOD protein. Its use in our experimental system confirms the prior RNA and enzyme activity measurements that indicate that our genetically selected long-lived strain has significantly higher levels of CuZnSOD protein than does the appropriate control strain.

Animals↗
PubMed2001

Inferring the trajectory of genetic variance in the course of artificial selection.

A method is proposed to infer genetic parameters within a cohort, using data from all individuals in an experiment. An application is the study of changes in additive genetic variance over generations, employing data from all generations. Inferences about the genetic variance in a given generation are based on its marginal posterior distribution, estimated via Markov chain Monte Carlo methods. As defined, the additive genetic variance within the group is directly related to the amount of selection response to be expected if parents are chosen within the group. Results from a simulated selection experiment are used to illustrate properties of the method. Four sets of data are analysed: directional selection with and without environmental trend, and random selection, with and without environmental trend. In all cases, posterior credibility intervals of size 95% assign relatively high density to values of the additive genetic variance and heritability in the neighbourhood of the true values. Properties and generalizations of the method are discussed.

Animals↗