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THE EFFECTS OF DISRUPTIVE AND STABILIZING SELECTION ON BODY SIZE IN DROSOPHILA MELANOGASTER. I. MEAN VALUES AND VARIANCES

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THE EFFECTS OF DISRUPTIVE AND STABILIZING SELECTION

ON

BODY

SIZE IN

DROSOPHZLA

MELANOGASTER.

I. MEAN VALUES AND VARIANCES

M. BOS

Genetisch Instituut der Rijksuniversiteit te Groningen, Haren ( G n ) , The Netherlands

A N D

W. SCHARLOO

Genetisch Instituut der Rijksuniversiteit, Utrecht, The Netherlands

Manuscript received December 11, 1972 Revised copy received July 27, 1973

ABSTRACT

Disruptive and stabilizing selection were applied to thorax and wing length in Drosophila mlanogaster. Disruptive selection with negative assortative mat- ing (D-) practiced on thorax length caused a large increase of the phenotypic variance; practiced on wing length the increase was less striking. Disruptive se- lection with random mating (DR) caused i n most lines only a temporary in-

crease in phenotypic variance, but mean values increased considerably. Sta- bilizing selection (S) on thorax length or wing length did not decrease the phenotypic variance, but the mean value of the selected character declined.- The proportion of flies emerging decreased in all lines, while development time increased. Variance of development time increased in the D--lines. In

both D--lines the frequency of flies with a n abnormal number of scutellars was high (> 60% i n one of the lines) and there was a temporary increase in ab- normal segmentation of the abdomen.

T H E properties of the phenotypic variance of a quantitative character have been determined by selection pressures on the character in the past (A. ROB-

ERTSON 1955, 1966; KEARSEY and KOJIMA 1967;

MATHER

1966). Natural selec-

tion can act on quantitative characters in various ways. In constant environ- mental conditions three different types of selection can be distinguished (MATHER 1953 and 1955) : directional selection, stabilizing selection and dis- ruptive selection.

Experiments investigating the effects of artificial stabilizing and disruptive se- lection are comparatively recent. These types of selection have been practiced on different characters. Most work has been done on morphological characters whose differentiation occurs within a short period of development, e.g., sternopleural bristle number (THODAY azd co-workers BOAM, GIBSON, MILLICENT and WOL- STCNHOLME. See THODAY 1959 and THODAY and GIBSON 1970) and the length of the fourth longitudinal wing vein of the mutant c P a (SCHARLOO 1964; SCHAR-

LOO, HOOGMOED and TER KUILE 1967). Both characters posses a simple genetic

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680 M. BOS A N D W. SCHARLOO

architecture: additive genetic variance is large, there is no or only a small vari- ance component caused by genetic interaction, and within-fly variance is high.

In these experiments the effects expected from stabilizing and disruptive selection were realized: striking changes in variance occurred. The results of other experi- ments on characters such as development time (PROUT 1962) and body weight (FALCONER and

ROBERTSON

1956), which are more closely bound to the general physiology of the organism during a relatively long period of the development, suggest that the results of these types of selection are dependent on the biological significance of the character selected for.

I n order to understand the role of stabilizing and disruptive selection in gen- erating the genetical architecture of populations, their effect on characters with different biological significance must be analyzed. Therefore it is worthwhile to extend the number of characters to which these types of selection have been ap- plied. We chose body size because much is known about this character (ROBERT-

SON and REEVE 1952;

ROBERTSON

1955). In contrast to sternopleural chaetae

number and ci D-G expression, body size is a character which is sensitive to a va-

riety of environmental factors and subject to inbreeding depression and heterosis. Because development time and body size are both measures of growth and be- cause parallel changes have been recorded in selection experiments ( ROBERTSON 1960)

,

the relationship of the two characters was studied in some of our lines.

MATERIALS A N D METHODS

The base population (Groningen, 1967) was founded in June 1967 by combination of the progenies of eighteen fertilized wild females in a population cage. These females had been caught in the fruit and vegetable market at Groningen.

The characters chosen as measures of body size were thorax length and wing length. Size measurements were carried out on live flies by the method of ROBERTSON and REEVE (1952), with the difference that wing length was measured as the length of the posterior segment of the fourth vein. One unit of size is always 0.01 mm. The flies were reared at 25 f 0.5" and 6CrSO% relative humidity in 50-ml culture bottles, which contained 15 ml food. A culture always contained less than 150 eggs. The culture medium had the following composition: water (1000 ml), agar (19 g), sugar (54 g), dried yeast (32 g) and nipagine (1.3 g) (MITTLER and BENNETT 1962). After gen- eration 42 (G 42) virgin flies were fed for three days with live yeast before being transferred t o the culture bottles. Each selection line consisted of four cultures (sublines). From each cul- ture samples of 20 9 9 and 20 8 8 were measured.

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DISRUPTIVE A N D STABILIZING SELECTION 68 1 lines S-5, DR-5 and C-5 were commenced in October 1968 and 0--6, DR-6 and C-6 in November 1969. Generation interval was kept at three weeks by a rigid procedure. Consequently in every generation the female parents were of the same age when laying eggs. When emergence of flies commenced, they were collected morning and evening to ensure that the majority was virgin and stored a t 17" until they were measured. If a culture failed to produce twenty flies of each sex, extra flies were measured from a second culture of the same parents. Occasionally a subline gave no progeny at all and flies from the other sublines had to be used.

Phenotopic variances of the character selected for were computed as within-sample variances in order to eliminate the differences between cultures. The variance was expressed as a squared coefficient of variation:

within culture standard deviation

x

100

mean

c.v.2

=

(

The use of this coefficient, which is independent of the unit of measurement and expressed as a percentage, is justified by the fact that males and females of the same stock are found t o have roughly equal coefficients of variation though they differ by about 15% in mean size (Bos, un-

published; REEVE and ROBERTSON 1953).The coefficient was squared t o get a measure compar- able to variance.

Eggs were coufited in all cultures. Mean egg production of selected females was computed over 24 hours. The percentage emergence was calculated as the proportion of eggs which yielded adults.

Times of development could he calculated from the emergence data by considering the mid- point of the egg laying period as the starting point of development. In G 74 of selection develop- ment time and thorax length were determined in a separate test for the base p3pulation ( B ) , con- trols (C-l and C-2) and the D- thorax selection lines (E--1 and 0-4). In the D- lines these characters were determined on progenies from cultures set up with larvae from (large 0 0 X small 8 8 ) and (small 0 9 x large 8 8 ) matings i n a 1: 1 ratio. Parent flies were well fed with live yeast, measured (and in the case of D- tests selected), mated, placed in vials with food medium for about 24 hours to void predeveloped eggs and put in oviposition bottles. Collected eggs were spread over the surface of the agar (1-2%) in petri dishes. For each type six cultures containing 40 larvae and two cultures with 60 larvae were set up whenever possible. Within each culture larvae were 0-2 hours old. The cultures were started on the same day ( B , C-Z), on two successive days (C-1, =-I) or on three successive days (D--2) and kept in a climate mom a t 25 t 0.5" and 70% relative humidity. Hatched flies were collected within the climate room every six hours (4,10,16 and 22 h.) and thorax length of all flies was measured.

Other characters such as scutellar bristle number and abdominal chitinization were occa- sionally observed.

RESULTS

Means-thorax lines: The means of the control lines and the selection lines are

given in Figure 1 . The average of the two control lines deviated only slightly from the value i n the base population. At the end of the selection period C-I was about two units above the mean in

G

0 and C-2 was 2.5 units below this value. Means of the selection lines are given as deviations from the mean of these two controls. Mean values of DR-3 and DR-4 are given as deviations from C-3, reared

concurrently with these selection lines.

In the stabilizing lines there was a decrease of the mean value. In the D R lines a n increase of the mean value occurred in all lines, but the increase started later in the second set of two lines (DR-3 and - 4 ) . Only after 22 generations of disrup- tive selection did the means of D--1 and 0--2 diverge.

(4)

682

VI

d

W

J 0

I z

0 U

c

M. BOS A N D W. SCHARLOO

THORAX LINES

105

100

1

90 I

- 4 4 1

0 5 10 15 20 25 30 35 U ] 45 50

OENERATIONS

FIGURE 1.-Thorax selection: The means of control and selection lines. C , controls; S, stabiliz- ing lines; DR and D-, disruptive lines. The values of the selection lines are given as deviations from simultaneous controls (sexes averaged, 1 unit = l / l O O mm).

(sexes averaged) were generally in agreement with those of the thorax lines; the mean increased in at least one of the DR lines and decreased in the S line (Figure

2 ) .

Phenotypic variability-thorax lines: The phenotypic within-culture variation

(5)

DISRUPTIVE A N D STABILIZING SELECTION 683

0 ~ 0

GENERATIONS

N 10

5

.5

2:

30

N 20 2:

10

I

GENERATIONS

FIGURE &.-Wing selection: The means and c.v.2 of control and selection lines. Arrows indi- cate a transfer of lines to another person. C-5, DR-5 and $5 were reared simultaneously, just as

C-6 and DE-6 (1 unit = 1/100 mm).

was no evidence of change in the C lines and in initial generations variability was remarkably constant. From G 30 onwards C-l and C-2 were not measured every generation.

I n all lines after G 15 occasionally very small flies occurred which had often a n abnormal phenotype with defective abdominal chitinization or incompletely developed wings. These flies caused incidental high variances (see also ROBERT-

SON 1955).

The variation in the S lines was certainly not lower than in the controls. In the

DR-1 line variation increased three times in two or three steps during the first 16

generations of selection, but dropped to control level after every peak. The decrease of the variance after the first peak

(DR-l

G 5, C . V . ~ = 14.43; G 8, C . V . ~ =

(6)

684

M. BOS A N D W. SCHARLOO

THORAX LINES - 1

,

v

1

c.1 c.2

04 , , , I , I

.

, , I

20

15

10

5

DR.2

oR.1

0 4

0 5 IO 15 20 25 30 35 LO 4 5 50 GENERATIONS

FIGURE 3.-Thorax selection: Variability (c.v.2) in the selection lines and their controls.

(7)

D I S R U P T I V E A N D S T A B I L I Z I N G S E L E C T I O N 685

, c . 2 A D-. 2

10

0

I30

go 100 110 120 90 IO0 110 120

FIGURE 4.-Thorax selection: Frequency distributions of females from the base population (G 0, 400 0 p from 11 cultures) and the 8 simultaneous lines (80 0 0 from 4 cultures). The abscissae show thorax length (1 unit = 1/100 mm), the ordinates percentage of females. Shaded portions indicate the selection imposed on the lines.

there a suggestion of bimodality (see 0--2 G 46, Figure 4)) but this was certainly a consequence of chance.

Wing lines: These lines were handled by three different persons. Transfers

from one person to another are indicated by arrows (Figure 2). In both D E lines

C . V . ~ was higher than in controls; and at least twice a steep drop of C . Y . ~ coincided

with a considerable increase in the mean value of wing length: DR-5 G

5,

DR-6

(8)

686

VI

(3

(3 W

LL

0 CY

W

r 3 z m

M. BOS A N D W. SCHARLOO

THORAX LINES

7 5 7

50

25

lool

75

50

100,

25 I I

1 7 6 9 1

2

I

15

li

4 3 a a g

m

ii

2 8 M l

GENE RAT IONS

FIGURE 5.-Thorax selection: Egg production per 0 in 24 hrs. and emergence percentage given as three-generation means. The single arrow indicates a generation in which incubator temperature was incidentally too high. After G 42, selected parental flies received live yeast ( t w o

arrows).

the exception of G 14, when only 71 instead of 160 flies could be measured). While the variance in the S line was below its control during the first ten genera- tions, there was a rise after G 14.

Egg production and emergence: Because both egg production and emergence

percentage are sensitive to even small changes in the environment, three-genera- tion means were computed. These values are plotted for the thorax lines in Figure

(9)

D I S R U P T I V E A N D S T A B I L I Z I N G S E L E C T I O N 687

TABLE 1

Mean number of adults produced in the copulation vials of the D- lines by the eight selected large 0 0 (crosses L x S ) and by the eight small 0 0 (crosses S

x

L)

Generations L X S

I 7-16(9) 114.6

t 17.8

I1 17-26(10) 52.6

& 13.6

I11 27-41(9) 81.9

t 14.0

D--I

S X L Diff. L X S

41.4 73.2 139.4

t 6.1 &18.8+ & 13.4

34.5 18.1 77.7

t 9.4 a16.5 t 1 4 . 7

54.0 27.9 86.4

t l l . 9 t 1 8 . 0 t 13.6

0-2

S X L

51.8 f 8.5 43.2 +- 13.1 53.6 f 7.6

-~ Diff.

87.6

15.91- 34.5

t 19.7 32.8

F 15.5*

* P

<

0.05.

+

P

<

0.01.

There was no indication of a difference in performance between the egg produc- tion of the S and

D R

lines and the control lines.

In all lines (controls included) the percentage emergence showed a strong downward trend during the initial 15-20 generations of selection. After that period emergence stabilized in most lines at a level of about 60-70%. I n the

D-

lines, especially, the small females produced only a small number of progeny (Table 1). The difference was particularly large in the first period. A similar difference between the large and small females was found in a test on G 10 and

G 11 of the DR-2 line (220 adults produced by 16 large 0 0 and 67 produced b y 16 small 0 0 ) .

Lines C-5, S-5, DR-5 and

D--5,

which were handled simultaneously, are the only wing lines for which emergence percentages are given (Figure 6 ) . A decrease in emergence percentage was found as in the thorax lines.

Other characters: It was noticed in G 23 that flies with more than four scutel-

lars were numerous in the

D-

and

D R

lines. Flies with less than

4

bristles were found only occasionally. Frequencies of flies with abnormal scutellar bristle num-

ber ( 5 o r 6 bristles; occasionally 3 or 7) averaged over three generations are

given i n Figure 7 for the D- lines and the controls. In the base population this

100,

WING LINES

c-5-

O ! 1 I I

0 5 10 15 20

GENERATIONS

(10)

688 M. BOS A N D W. SCHARLOO

THORAX LINES

GENERATIONS

FIGURE 7.-Thorax selection: Percentage of flies ( 9 9 ) having more or less than four scutel- lar bristles. Three-generation means are given from G 23-G 61.

frequency was lower than 0.5% (Bos et al. 1969) ; in G 23 or G 24 in the S-1 and

S-2 line. respectively, 2.5% and 1.3% were found; in DR-1 and DR-2, 7.4% and 10.7%. I n the generations 50-70 the thorax length was determined separately in females with normal and with increased bristle number. Females with more than

4 scutellars were larger in both D--1 and D--2 (with a WILCOXON’S signed rank test in D--I, P = <0.05; in D--2, P = 0.05).

Phenodeviants with abnormal segmentation or chitinization of the abdomen occurred in low frequency in the base population. Following observance of an increase of their frequency in G 7 of the D - 1 line, all flies of the thorax lines were scored for this character (Figure 8). I n D--1 frequency of “abnormal abdomen” was then higher than in any other line, but decreased to the same level at the end of the selection. Correlation coefficients between thorax length and degree of “abnormal abdomen” were about -0.20 in both

D-

lines, but far from significant at the 5% level (d.f. = 38).

In Table 2 development time is given f o r control and D- lines in four different periods of selection. In all lines presented development time increased, but the increase was more pronounced in the selection lines than in the controls. Vari- ability of development time tended to be higher in the D-lines than in the C lines. It was observed that in the C and in the D- lines small flies often hatched later than large flies. This was confirmed in an experiment performed simultaneously with G 74 (Table 3). Variances of thorax length and developmental time were larger in the

D-

lines than in controls and the base population. A negative corre-

(11)

D I S R U P T I V E A N D S T A B I L I Z I N G S E L E C T I O N

THORAX LINES

689

o i , , , , ,

21 23 25 Y 37 LO

GENERATIONS

FIGURE 8.-Thorax selection: Percentage of flies ( 0 0 ) with abnormal abdominal chitiniza- tion or segmentation. Three-generation means are given from G 7. C gives the average of C-2 and C-2.

ences between the correlation coefficients of replicate cultures, but their averages were also negative.

DISCUSSION

The results of our experiments differ in important respects from those of other experiments on disruptive and stabilizing selection (e.g., THODAY 1959; SCHAR- LOO, HOOGMOED and TER KUILE 1967). In our experiments, stabilizing selection

(S) on body size did not cause a decrease of the phenotypic variance. At least in

TABLE 2

Mean time o f development

(l)

in hours and pooled within-culture uariances

(a,)

in the D-

selection lines and controls. Only the values of females are giuen. Within brackets are the numbers of flies

Controls D- lines

1 2 - 1 - 2

Generation interval 87 SZd 2 SZd d Szd d

5-1 0 232.5 W1.0 234.3 177.9 244.0 325.8 240.0 225.9

k4.5 (983) -15.0 (1027) -16.5 (579) -14.3 (952)

20-25 239.8 273.0 237.3 416.5 252.2 527.1 257.3 510.0 a4.0 (776) I 4 . 6 (738) t 4 . 8 (628) k4.0 (620)

4Q-47 246.1 316.5 241.0 271.5 249.0 348.7 248.8 340.2

23.8 (943) k3.9 (1268) k3.3 (901) k2.1 (1170) 52-59 237.7 231.2 235.0 187.8 2449.7 369.3 251.1 374.8

(12)

TABLE 3 Thorax length (in 0.01 mm) and deuelopment time (hours between hatching of eggs and emergence of flies) in the Groningen 1967 base population (B), in the D- thorax selection lines and their controls. G 74 Mean Variance ? d P time d Thorax length ;fhorax length d time d B 106.8 92.6 213.6 220.4 c-1 104.9 91.8 206.0 211.4 c-2 103.3 89.0 209.5 216.8 P-I 113.6 98.9 217.1 223.9 D--2 109.7 95.2 217.2 219.5 [O--Cl * * 3.27 2.95 89.7 56.2 4.70 2.01 103.5 36.2 1.97 3.19 44.3 49.2 7.27 4.34 154.1 91.2 9.89 8.90 180.6 114.0 * *

Correlation coefficients

?TnoraX/Dev. d -0.07 +O.O+ -0.w +OM -0.05 -0.25 -0.15-f -0.31 -0.47 -0.22 Numbers

td

5?

Of file d 9 160 141(8) 138 112(7)

3

160 124(8) v) 120 91(8) 63 57(7)

E

$

E!

(13)

DISRUPTIVE A N D STABILIZING SELECTION 691

one line there was an increase. Body size decreased in all stabilizing selection lines. Disruptive selection with random mating ( D E ) caused only temporary increase of the phenotypic variance, while there was a strong increase of body size. Polymorphism (bidomal frequency distributions) or isolation were not observed in our

DR

lines. Only in the lines in which disruptive selection with negative assortative mating ( D - ) was practiced on thorax length, did a sustained and large increase of the phenotypic variance occur, Our results are more similar to the results of PROUT (1962), obtained by selection on time of development in Drosophila.

The features of our experiments can only be explained after further analysis of the changes in the selection lines. In the next paper it will be shown that they are at least partly a consequence of the peculiar properties of our quantitative character. These properties are expounded in the extensive work of

ROBERTSON

and REEVE (see, e.g.,

F. W.

ROBERTSON

1955).

In our DE-2 and DE-2 lines the mean increased by 8-12 units. This was a similar or even a larger increase than obtained by

F.

W. ROBERTSON (1955) by directional selection. This is surprising even although the Groningen 1967 base population has a higher genetic variance than ROBERTSON’S base populations

(F.

W.

ROBERTSON 1955; Bos and SCHARLOO 1973). The directional effect of our disruptive selection was probably a consequence of the fact that large females produced more progeny than small females. Genomes producing small flies will have decreased in frequency. As a consequence the increase in phenotypic vari- ance in the first generations of selection was lost again, when mean thorax length increased. A preceding period of disruptive selection seems to promote an exhaus- tive use of the genetic variability of the base population by directional selection. In DE-3 and DR-4, where the mean did not rise to such a high level, a relatively large variance was maintained.

Increase of phenotypic variability occurred in both D- thorax lines. It will be shown in the next paper that the underlying mechanism is quite different in the two lines. Nevertheless changes in other characters were similar in both, although they sometimes differed in extent. The initial reduction in reproductive success was mainly the result of the low production of flies by the small females. In both lines a high frequency of flies with an abnormal number

(#4)

of scutellar bristles was observed: in D--2 a continuous upward trend, in 0--2 a rather con- stant high level. There existed a positive correlation between thorax length and number of scutellars in both

D-

lines. A positive correlation between size and bristle number is found by several authors (NEEL 1940; REEVE and ROBERTSON

1954; SPICKET 1963). Since scutellar bristle number is known to be strongly canalized (RENDEL 1953)

,

the occurrence of abnormal numbers of scutellars could be interpreted as an indication of a general disturbance in the development

(14)

692 M. BOS A N D W. SCHARLOO

ment time in both

D-

lines, a general effect on development and growth of dis- ruptive

(D-)

selection can be concluded.

The authors are grateful to PROFESSOR W. J. FEENSTRA and DR. W. VAN DELDEN for their criticism of the manuscript. They also thank MRS. LAURENCE WILDEBOER-DUPUI for technical as- sistance; MR. K. EZINGA who made many of the calculations; and MR. H. MULDER for preparing the figures. Finally, we wish to thank MARIJKE TOLBOOM-MINNEMA, Jo STEEGEN and CHERT VAN

DIJKEN for doing part of the selection work.

L I T E R A T U R E CITED

Bos, M., 1969

Bus, M., W. SCHARLCQ, R. BIJLSMA, I. M. DE BOER and J. DEN HOLLANDER, 1969

The effect of disruptive and stabilizing selection on body size in Drosophila

melanogasier. Drosophila Inform. S e n . 44: 105.

Induction of morphological aberrations by enzyme inhibition in Drosophila melanogaster. Experientia 25: 811-813.

The effects of disruptive and stabilizing selection on body size

in Drosophila melanogaster. 11. Analysis of responses in the thorax selection lines. Genetics

FALCONER, D. S., 1957 Selection for phenotypic intermediates in Drosophila. J. Genet. 55: 551- 561.

FALCONER, D. S. and A. ROBERTSON, 1956 Selection for environmental variability of body size in mice. Z. Vererb. 87: 385-391.

KEARSEY, M. J. and KEN-ICHI KOJIMA, 1957 The genetic architecture of body weight and egg

MATHER, K., 1953 The genetical structure of populations. Symp. Soc. Exptl. Biol. 7: 66-95. Polymorphism as an outcome of disruptive selection. Evolution 9: 52-61. Variability and selection. Proc. Roy. Soc. London B 164: 328-340.

A simple food medium that requires no live yeast with the

The interrelations of temperature, body size and character expression in

The effects of stabilizing selection on the time of development i n DrosophiZa

Studies in quantitative inheritance. 11. Analysis of

-,

Studies in quantitative inheritance. VI. Sternite chaeta number in Drosophila: a

Bos, M. and W. SCHARLOO, 1973

7 5 : 695-708.

hatchability in Drosophila melanogaster. Genetics 56 : 23-37.

-,

-

,

minimum of variables. Drosophila Inform. Serv. 36: 131.

Drosophila melanogaster. Genetics 25 : 225-250.

melanogaster. Genet. Res. 3 : 364-382.

a strain of Drosophila melanogaster selected f o r long wings. J. Genet. 51: 276-316. 1954

metameric quantitative character. Z. Vererb. 86: 269-288. 1955

1966

MITTLER, S. and J. BENNETT, 1962

NEEL, JAM= V., 1940

PROUT, T., 1962

REEVE, E. C. R. and F. W. ROBERTSON, 1953

RENDEL, J. M., 1959 ROBERTSON, A., 1955

Canalization of the phenotype of Drosophila. Evolution 13: 425-439. Selection in animals: Synthesis. Cold Spring Harbor Symp. Quant. Biol. 20: 225-229. -, 1966 Artificial selection in plants and animals. Proc. Roy. SOC. London B 164: 341-349.

Selection response and the properties of genetic variation. Cold Spring Harbor Symp. Quant. Biol. 20: 166-177. - , 1960 The ecological genetics of growth in Drosophila. I. Body size and development time on different diets. Genet. Res. 1 : 288-304.

Studies in quantitative inheritance. I. The effects of selection of wing and thorax length in Drosophila melanogaster. J. Genet. 50: 414448. The effect of disruptive and stabilizing selection on the expression of a cubitus interruptus mutant i n Drosophila. Genetics 50: 553-562.

ROBERTSON, F. W., 1955

ROBERTSON, F. W. and E. C. R. REEVE, 1952

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D I S R U P T I V E A N D S T A B I L I Z I N G S E L E C T I O N 693

Stabilizing and disruptive selection on a mutant character in Drosophila. I. The phenotypic variance and its components. Genetics 56: 709-726.

Genetics and developmental studies of a quantitative character. Nature 199: 870-873.

Effects of disruptive selection. I. Genetic flexibility. Heredity 13: 187-203. The probability of isolation by disruptive selection. Am.

Corresponding Editor: T. PROUT SCHARLOO, W., M. S. HOOGMOELI and A. TFA KUILE, 1967

SPICKET, S. G., 1963

THODAY, J. M., 1959

Figure

FIGURE 1.-Thorax ing lines; from simultaneous controls (sexes averaged, selection: The means of control and selection lines
FIGURE &.-Wing selection: The means and C-6 cate a transfer c.v.2 of control and selection lines
FIGURE 3.-Thorax selection: Variability (c.v.2) in the selection lines and their controls
FIGURE 4.-Thorax abscissae 0, 400 selection: Frequency distributions of females from the base population (G 0 p from 11 cultures) and the 8 simultaneous lines (80 0 0 from 4 cultures)
+6

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