Correlated responses to selection on body size in Drosophila 
melanogaster

Correlated responses to artificial selection on body size in Drosophila melanogaster were investigated, to determine how the changes in size were produced during development. Selection for increased thorax length was associated with an increase in larval development time, an extended growth period, no change in growth rate, and an increased critical larval weight for pupariation. Selection for reduced thorax length was associated with reduced growth rate, no change in duration of larval development and a reduced critical larval weight for pupariation. In both lines selected for thorax length and lines selected for wing area, total body size changed in the same direction as the artificially selected trait. In large selection lines of both types, the increase in size was achieved almost entirely by an increase in cell number, while in the small lines the decrease in size was achieved predominantly by reduced cell size, and also by a reduction in cell number. The implications of the results for evolutionary-genetic change in body size in nature are discussed.

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Cellular basis and developmental timing in a size cline of Drosophila melanogaster.

Genetics ◽

10.1093/genetics/140.2.659 ◽

1995 ◽

Vol 140 (2) ◽

pp. 659-666 ◽

Cited By ~ 5

Author(s):

A C James ◽

R B Azevedo ◽

L Partridge

Keyword(s):

Drosophila Melanogaster ◽

Body Size ◽

Development Time ◽

Larval Density ◽

Cell Number ◽

Laboratory Culture ◽

Wing Area ◽

Thorax Length ◽

Selection Processes ◽

Genetic Cline

Abstract We examined 20 Drosophila melanogaster populations collected from a 2600-km north-south transect in Australia. In laboratory culture at constant temperature and standard larval density, a genetic cline in thorax length and wing area was found, with both traits increasing with latitude. The cline in wing area was based on clines in both cell size and cell number, but was primarily determined by changes in cell number. Body size and larval development time were not associated among populations. We discuss our results in the context of selection processes operating in natural and experimental populations.

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Selection for lean growth rate and correlated responses in litter traits in a synthetic line of Yorkshire-Meishan pigs

Canadian Journal of Animal Science ◽

10.4141/a00-082 ◽

2001 ◽

Vol 81 (2) ◽

pp. 205-214 ◽

Cited By ~ 6

Author(s):

P. Chen ◽

T. J. Baas ◽

J. C. M. Dekkers ◽

L. L. Christian

Keyword(s):

Growth Rate ◽

Regression Coefficients ◽

Correlated Response ◽

Selection Line ◽

Control Line ◽

Correlated Responses ◽

Lean Growth ◽

Litter Traits ◽

Selection For ◽

Synthetic Line

Selection for lean growth rate (LGR) was conducted for four generations in a synthetic line of Yorkshire-Meishan pigs to study the effectiveness of selection for LGR and correlated responses in litter traits. Lean growth rate was estimated from ultrasound measurements of 10th-rib backfat thickness and longissimus muscle area. In the selection line, 7 boars and 20 gilts with the highest LGR were selected to produce the next generation. The generation interval was 13 mo and the average selection differential per generation was 1.1 phenotypic standard deviation units. A contemporaneous control line was maintained by randomly selecting 5 boars and 15 gilts. Data from a total of 1057 pigs sired by 58 boars and out of 133 sows were available from the two lines. Selection responses were estimated from deviations of the selection line from the control line using least squares (LS) and by multiple trait derivative-free restricted maximum likelihood analysis using an animal model (AM). The estimate of response to selection per generation using LS was 9.4 ± 0.95 g d–1 for LGR. The corresponding estimate from the AM was 9.8 ± 0.51 g d–1. Correlated responses in litter traits were regressed on generation. For the LS method, regression coefficients were negative but not significant (P > 0.05) for total number born, number born alive, and number at 21 d and at 42 d. Significant, positive correlated responses occurred in 42-d litter weight and 21-d piglet weight (P < 0.05). For the AM method, the regression coefficients were also negative, but were not significant (P > 0.05) for numberalive at birth, at 21 d, and at 42 d. A significant positive correlated response occurred only for 42-d litter weight (P < 0.05). Although results are based on a population of limited size, it can be concluded that selection for LGR in a synthetic line is effective and should have little effect on litter traits. Key words: Pigs, selection, lean growth rate, correlated response

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Changing the relative size of the body parts of Drosophila by selection

Genetics Research ◽

10.1017/s0016672300034972 ◽

1962 ◽

Vol 3 (2) ◽

pp. 169-180 ◽

Cited By ~ 36

Author(s):

Forbes W. Robertson

Keyword(s):

Body Size ◽

Relative Size ◽

Cell Number ◽

High Ratio ◽

Growth Patterns ◽

The Body ◽

Mass Selection ◽

Body Parts ◽

Wing Size ◽

Thorax Length

1. Mass selection for both high- and low-ratio of wing to thorax length has been carried out on a population of Drosophila melanogaster. The response to selection was immediate and sustained. When the experiment was stopped after ten generations, the wing area in the two selected lines differed by about 30%. The heritability estimate worked out at 0·56 ± 0·08.2. Thorax length remained comparatively unchanged during selection nor was there any change in wing shape. There was some evidence of assymetry of response since there was a relatively greater change in favour of smaller rather than larger size.3. The tibia length of all pairs of legs showed correlated changes so that the lines with larger or smaller wing sizes had also larger and smaller legs.4. The normal allometric relation between wing and thorax length, associated with variation in body-size, apparently also changed, so that for a given change in thorax length there was a greater or smaller proportional change in wing size in the high- or low-ratio lines.5. The changes in relative wing size are due to changes in cell number.6. It is suggested that the genetic changes due to selection act in the early pupal period when the imaginal discs are undergoing differentiation and proliferation to form imaginal hypoderm and appendages.7. Tests of genetic behaviour failed to show any departure from additivity in crosses which involved the unselected population and the high-ratio line. But highly significant departures existed in the cross to the low-ratio line. Relatively smaller wing size behaves as largely recessive. Stability of the normal wing/thorax ratio involves dominance and probably also epistasis. The genetic properties of the relative size of the appendage are apparently similar to those which characterize body-size as a whole.8. It is suggested that selection provides a valuable tool for studying the constancy or lability of the growth patterns which determine morphology.

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