Artificial selection with differing population structures

Rathie, K. A.; Nicholas, F. W.

doi:10.1017/s0016672300019753

Cited by 18 publications

(8 citation statements)

References 21 publications

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“…The selection lines were originally established in another experiment (Rathie & Nicholas, 1980). The base was a large cage population of the sc Canberra strain of Drosophila melanogaster, derived from the Canberra strain (Sheridan et al 1968) by introducing sc (scute) and y z (yellow body) through repeated backcrossing to make bristle scoring easier and to provide a check against contamination (Rathie, 1969).…”

Section: Methodsmentioning

confidence: 99%

Long-term selection for a quantitative character in large replicate populations ofDrosophila melanogaster: 1. Response to selection

Yoo

1980

Genet. Res.

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The response to long-term selection for increased abdominal bristle number was studied in six replicate lines of Drosophila melanogaster derived from the sc Canberra outbred strain. Each line was continued for 86-89 generations with 50 pairs of parents selected at an intensity of 20 %, and subsequently for 32-35 generations without selection. Response continued for at least 75 generations and average total response was in excess of 36 additive genetic standard deviations of the base population (cr A ) or 51 times the response in the first generation. The pattern of longterm response was diverse and unpredictable typically with one or more accelerated responses in later generations. At termination of the selection, most of the replicate lines were extremely unstable with high phenotypic variability, and lost much of their genetic gains rapidly upon relaxation of selection.The variation in response among replicates rose in the early phase of selection to level off at approximately 7-6 a\ around generation 25. As some lines plateaued, it increased further to a level higher than would be accommodated by most genetic models. The replicate variation was even higher after many generations of relaxed selection. The genetic diversity among replicates, as revealed in total response, the individuality of response patterns and variation of the sex-dimorphism ratio, suggests that abdominal bristle number is influenced potentially by a large number of genes, but a smaller subset of them was responsible for selection response in any one line.

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Section: Methodsmentioning

confidence: 99%

Long-term selection for a quantitative character in large replicate populations ofDrosophila melanogaster: 1. Response to selection

Yoo

1980

Genet. Res.

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“…The proportion of initial families eliminated during selection was no less in the present SW sublines and Jones' (1969b) previously selected populations than in comparable selection lines at an early stage of selection (Jones I969a;Rathie 1976), although selection response was much slower in the former. This perhaps suggests that replacing the failed matings was not sufficient to restrain the overriding influence of natural selection in the former, as the replacements were mostly unrelated to the failed matings.…”

Section: Discussionmentioning

confidence: 88%

“…In fact, the average reduction in effective population size was only 6·4 % on a single generation basis, a marked contrast with 13·1 % estimated in early generations of selection (Rathie 1976). As the inbreeding effect of selection is known to accumulate in successive generations (Robertson 1961), the more appropriate parameter for a selection line seems to be the realized effective popUlation size estimated from observed inbreeding coefficients during the whole period of selection.…”

Section: Discussionmentioning

confidence: 89%

Long-Term Selection for a Quantitative Character in Large Replicate Populations of Drosophila Melanogaster. V. The Inbreeding Effect of Selection

Yoo¹

1980

Aust. Jnl. Of Bio. Sci.

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Four replicate lines of D. melanogaster, which had been selected for increased abdominal bristle number for 58 or 69 generations, were pedigreed for nine generations under selection with or without replacements for failed matings (SW and SO sublines) and under relaxed selection also with or without replacements (RW and RO sublines).Natural selection was effective in reducing mean bristle number in both R Wand RO sublines (except in one line), but its opposition to artificial selection in SW and SO sublines appeared to be only indirect. The relation between the two selective forces was inferred from their effects on effective population size, the comparison of selection responses in SW and SO sublines, and the difference between expected and realized selection differentials.Fertility was the most important factor affecting variance effective population size, while fecundity (with upper limits on the number of offspring scored) and artificial selection were in most sublines similar in their relative importance. Measured by reduction in effective population size, the inbreeding effect of artificial selection confined to the immediate generation was small (6·4%), but the cumulative effect estimated from the observed rate of inbreeding was quite large (16 %), tending to increase with more response.The spread of genes from initial families seems to have been influenced by both artificial and natural selection. Correlations between the mean score of an initial family and its genetic contribution indicate that additive genetic variance was still available at this stage of selection. The number of initial families represented in SW and SO sublines was generally large even after nine generations, and few families made unusually large contributions.

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“…Such a result is predicted from multiple-peak epistasis (Wright, 1939), but only ifit is assumed that 1) at the onset of selection, a population is likely to be in the domain ofattraction ofan inferior adaptive peak (i.e., one that is not as different in phenotype from the base population as other adaptive peaks) and 2) drift occurring within such subdivided lines is likely to move a population from its current domain ofattraction into that ofa superior adaptive peak (see Enfield and Anklesaria, 1986). The prediction has been confirmed by one experiment involving selection on body weight in Drosophila melanogaster (Katz and Young, 1975), but all other such experiments, involving selection in Tribolium (Enfield, 1970;Goodwill, 1974;Katz and Enfield, 1977) and in Drosophila (Madalena and Robertson, 1975;Rathie and Nicholas, 1980) have failed to support the deduction. These negative results may be interpreted as indicating that multiple epistatic peaks do not exist under most artificial selection regimes (and presumably under most regimes of natural selection) or that the above assumptions do not hold.…”

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confidence: 92%

A Test of the Role of Epistasis in Divergence Under Uniform Selection

1989

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Abstract. -Five populations of Drosophila melanogaster have previously been shown to be replicably different in their responses to artificial selection for knockdown resistance to ethanol fumes (Cohan and Hoffmann, 1986). The present study tests whether this divergence could be attributed to the epistatic mechanism assumed by Wright's shifting-balance model of evolution, in which alleles favored in the genetic background of one population are not favored in that of another. If this were the mechanism of divergence, crosses between selected lines from different populations would be expected to yield an epistatic loss of the selected phenotype. However, all such crosses showed a good fit to an additive model with dominance. Divergence by an epistatic mechanism may also be associated with epistatic variance within populations, but no evidence for such epistasis was found. The populations therefore appear to have responded in different ways to selection not because of epistasis but because knockdown-resistance alleles that were common in some populations were absent (or at least less common) in others.

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Artificial selection with differing population structures

Cited by 18 publications

References 21 publications

Long-term selection for a quantitative character in large replicate populations ofDrosophila melanogaster: 1. Response to selection

Long-term selection for a quantitative character in large replicate populations ofDrosophila melanogaster: 1. Response to selection

Long-Term Selection for a Quantitative Character in Large Replicate Populations of Drosophila Melanogaster. V. The Inbreeding Effect of Selection

A Test of the Role of Epistasis in Divergence Under Uniform Selection

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