Gene–environment interaction for body size and larval density in Drosophila melanogaster: an investigation of effects on development time, thorax length and adult sex ratio

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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The ecological genetics of growth in Drosophila 1. Body size and developmental time on different diets 1. Body size and developmental time on different diets

Genetics Research ◽

10.1017/s0016672300000264 ◽

1960 ◽

Vol 1 (2) ◽

pp. 288-304 ◽

Cited By ~ 70

Author(s):

Forbes W. Robertson

Keyword(s):

Body Size ◽

Development Time ◽

Small Body ◽

Growth Period ◽

Developmental Time ◽

Ecological Genetics ◽

Genetic Differences ◽

Environment Interaction ◽

Gene Environment Interaction ◽

Gene Environment

1. The interrelations between environment and the phenotypic expression of genetic differences have not received the attention they merit. Laboratory studies in quantitative inheritance, either by choice of character or experimental conditions, have not shed much light on this problem. Selection for the same character in different environments is likely to involve qualitative differences in physiology and development. Comparative study of such changes will throw light on the genetics of development generally, which in turn is relevant to how far the selection response can be pushed in a given direction. Since statistical variation between individuals must ultimately be interpreted in biological terms, the unnatural barriers between quantitative and physiological genetics must be broken down to clear the way for a greater variety of experimental analysis and a more widely based approach to the interpretation of individual differences in populations. The ecology of the animal provides the point of departure and guide to the kind of environmental variation which should be studied first. Since the suggested approach cuts across the conventional limits of quantitative, physiological and population genetics and exploits the concepts and methods of these alternative approaches to a common end, it is convenient to have a descriptive label. The term ‘ecological genetics’ has been adopted.2. This introductory paper is the first of a series dealing with experiments orientated along these lines. Since environmental variation largely consists of variation in the quantity and composition of the diet, the growth of individuals from a cage population of Drosophila melanogaster and also other strains has been studied on a variety of aseptic, synthetic diets. Body size and duration of the larval period are taken as measures of growth. There is a well-marked ability to regulate body size, by extending the duration of development, provided the diet is not too deficient. When the diet is further reduced development time is further lengthened and body size is reduced as well.3. To test for genetic differences in reaction to the diet, strains have been created by selecting for large or small body size, and their performance, together with that of the cross between them, has been compared with the performance of unselected individuals on alternative diets for the first few generations of mass selection. There is evidence of gene-environment interaction quite early in selection, and after six generations striking differences were detected. It is concluded that genetic differences in reaction to different sub-optimal diets are widespread in the population.4. The within-culture variance is increased by growing larvae on progressively more deficient diets and is approximately twice as great on a low-protein diet as on the usual live yeast medium. This increase is attributed to the segregation of genetic differences which are unimportant and contribute little to the variance under more favourable conditions.5. Comparison of body size and development time in repeated tests with two diets lacking fructose or deficient in ribonucleic acid revealed evidence of a plasticity of response to minor nutritional variation which is characterized by a positive association between body size and the duration of the growth period. This relationship is the reverse of that associated with crude variation in the diet which leads to a negative association between development time and body size. This plasticity of response probably represents an aspect of physiological homeostasis. Genetic differences in the magnitude and direction of this response probably contribute to gene-environment interaction generally, and this probably accounts for apparent discrepancies in alternative estimates of the response to selection for large and small body size when these are based on deviations from the unselected. This suggests the need for determining how far body size may be increased either by altering the growth rate or by extending the growth period, and also how far strains differentiated in such respects differ in their reaction to controlled differences in nutrition.

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The ecological genetics of growth in Drosophila V. Gene-environment interaction and inbreeding

Genetics Research ◽

10.1017/s0016672300000902 ◽

1961 ◽

Vol 2 (3) ◽

pp. 424-430 ◽

Cited By ~ 5

Author(s):

S. S. Prabhu ◽

F. W. Robertson

Keyword(s):

Body Size ◽

Inbred Lines ◽

Ecological Genetics ◽

Environment Interaction ◽

Protein Levels ◽

Gene Environment Interaction ◽

Gene Environment ◽

The Pacific ◽

Cage Population ◽

Synthetic Media

1. The growth of a number of inbred lines from the Pacific cage population have been compared under different conditions of temperature and nutrition. Body size and duration of the larval period were taken as measures of performance. Sub-optimal diets were provided by growing larvae on chemically defined synthetic media.2. Gene-environment interaction is widespread and often very great. The phenotypic effects of inbreeding on body size, even on a live yeast medium, may be greatly influenced by temperature. In one set of comparisons, inbred lines averaged 20% smaller at 25° C. but only 3% smaller at 18° C.3. Sub-optimal diets of different chemical composition, which lead to about the same average decline in body size, may differ greatly in the level of heterogeneity of response among the same set of inbred lines. Thus much greater heterogeneity was found on diets deficient in RNA than on diets with low protein levels. Such information is a useful guide to further study of gene-environment interaction in the outbred population.4. Diets which lead to a decline in body size of flies of the foundation population do not necessarily cause greater proportional decline on the part of inbred lines. Individual lines have been encountered in which body size is quite unaffected by changes in diet which reduce the size of the outbred flies by 25% or more.5. A series of crosses between lines from the same foundation population showed a striking level of homeostasis. The average body size and development time of the F1's was close to that of the population of flies on the favourable and two alternative sub-optimal diets. Also, compared with the parent lines, there was little evidence of gene-environment interaction among the crosses.

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The ecological genetics of growth in Drosophila 7. The role of canalization in the stability of growth relations

Genetics Research ◽

10.1017/s0016672300001063 ◽

1964 ◽

Vol 5 (1) ◽

pp. 107-126 ◽

Cited By ~ 23

Author(s):

Forbes W. Robertson

Keyword(s):

Body Size ◽

Phenotypic Variation ◽

Larval Growth ◽

Exponential Phase ◽

Larval Period ◽

Environment Interaction ◽

Adult Size ◽

Gene Environment Interaction ◽

Gene Environment ◽

The Difference

1. Similar changes in the body-size of Drosophila melanogaster have been achieved by different developmental pathways, especially either by altering the duration of the early exponential phase of larval growth or by influencing the growth rate in the phase which is independent of time.2. Such changes have been effected by selecting in the same population for larger or smaller size or shorter development time on chemically defined media, deficient in alternative nutrients. Selection for larger size on media deficient in protein or choline does not involve correlated changes in the larval period, whereas selection on media deficient in RNA does. The evidence suggests that shortage of this nutrient may be uniquely favourable for promoting a correlated change between body-size and duration of the larval period.3. Strains which differ in presence or absence of such correlation are characteristically different with respect to gene-environment interaction. In the former, the differences due to selection are generally more fully or completely expressed when the diet is changed whereas in the latter this is not so, and different, especially competitive condition, leads to a drastic reduction of the difference.4. How far the expression of the differences due to selection are affected, when the diet is altered, is also influenced by how long selection has been carried out. In early generations, the difference is only or best expressed in the special conditions provided during selection, but later on the changes due to selection are either fully expressed or partly so, as noted above.5. Many of the differences in gene-environment interaction between selected strains can be accounted for in terms of variation in the duration of the exponential phase. Thus two lines selected for small body-size on low RNA or low protein diets responded in different ways to the same nutritional change—one became relatively larger and took porportionately longer to develop, the other became relatively smaller and developed in a shorter time.6. There is clear evidence from various tests in which the amino-acid composition of the diet has been altered, that the nutritional requirements in the two stages of growth are not identical and this is consistent with the evidence for considerable genetic independence as well.7. It is proposed that the first stage of larval growth, which principally determines the duration of the larval period and may also influence body-size, is canalized. Genetic variation which can influence this stage is present in the population but contributes little to the phenotypic variation of adult size, except under special nutritional conditions as when ribonucleic acid is the sole limiting nutrient. But, at the same time, such canalization is dynamic in the sense that the absolute amount of growth which is completed in the first stage may vary with respect to diet and thereby lead to correlated variation in the duration of larval life and adult size. But individuals of an adapted population behave alike in this respect so that gene-environment interaction which leads to correlated variation in the two characters is of a very low order.8. The canalized phase sets a limit to the potential growth in the later stage and thereby influences greatly the mean value about which such growth is equilibrated. This canalization plays a major role in the general stability of growth relations and body-size although this is normally concealed by the high level of phenotypic variation. This interpretation can account for a great variety of data and provides a rational guide to further analysis.

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