scholarly journals The ecological genetics of growth in Drosophila 2. Selection for large body size on different diets

1960 ◽  
Vol 1 (2) ◽  
pp. 305-318 ◽  
Author(s):  
Forbes W. Robertson
Keyword(s):  
Body Size ◽  
Egg Production ◽  
Large Body ◽  
Selection Response ◽  
Ecological Genetics ◽  
Response To Selection ◽  
Genetic Changes ◽  
Alternative Pathways ◽  
Selection For ◽  
Live Yeast

1. Strains from a cage population of Drosophila melanogaster were selected for increased body size on the live yeast medium and on two aseptic synthetic media, (1) deficient in protein and (2) with all nutrients reduced to one-third the normal concentration required for growth to normal size. Both these media reduce body size by about 25%.2. In two strains, mass selected on the live yeast medium, the response continued fairly steadily for at least sixteen generations, when the experiment was discontinued. By this time body size had been increased by some 30%.3. On the sub-optimal diets the number of selected parents per generation was twice as great as on the live yeast medium, for technical reasons, but the response ceased abruptly after seven or eight generations of selection at a level considerably below that attained by the strains selected on the more favourable diet. Also, when selection was continued on the live yeast diet, no further progress occurred.4. Flies selected on the different diets and also unselected flies have been grown on the alternative conditions to see how the deviation from unselected is affected. For both strains selected on sub-optimal diets, the deviation from unselected is appreciably greater on the medium used for selection than on the live yeast medium.5. The response to selection for larger body size on deficient diets can be attributed partly to better adaptation to these conditions. This inference is supported by several lines of evidence. The within-culture variance, which is clearly greater when selected flies are grown on deficient diets, declines with effective selection. Also in the low-protein strain, for which data are available, the duration of the larval period is shortened in the early stages of selection, while egg production considerably exceeds that of unselected flies grown on the same diet.6. Other effects, of the kind normally selected for on the live yeast medium, also contribute to the variation and selection response on the deficient diets. At first they appear to act more or less independently of the genetic changes which favour increased size via improved adaptation to the diet, but continued selection soon leads to mutual incompatibility between the alternative pathways in growth. Since no further progress occurred when selection was continued on the live yeast medium, the earlier selection had probably lowered the level of adaptation to the live yeast medium. A new genetic situation had been created in which it was impossible to gauge the amount of further progress by reference to the behaviour of strains selected on the live yeast medium from the beginning.7. Estimates of heritability, based on cumulated selection differentials, are rather similar in the different diets and range between 0·30 and 0·38. On the live yeast medium, the estimate provides a fair guide to future progress, whereas, on the deficient diets, the predictive value is nil since response ceases immediately after the generations which provide the data for the estimates.8. By comparing the deviation from unselected on the media used for selection and also the other media, alternative estimates of genetic correlation in performance in different conditions can be computed. The estimates were sufficiently divergent to cast doubt on the practical utility of the statistical procedure, which takes no account of the likelihood that individual variation in body size in different environment represents to greater or lesser degree the effects of segregation on different processes of growth and metabolism.9. Since the course of selection is influenced by nutritional conditions, comparisons of response to selection for the same ‘character’ such as body size, in populations or species adapted to different conditions, must allow for the likelihood that unequal differences between the conditions in which selection is carried out and those in which the animal normally lives may be an important cause of differences in response.

scholarly journals The ecological genetics of growth in Drosophila 8. Adaptation to a New Diet

1966 ◽  
Vol 8 (2) ◽  
pp. 165-179 ◽  
Author(s):  
Forbes W. Robertson
Keyword(s):  
Body Size ◽  
Egg Production ◽  
Development Time ◽  
Chelating Agent ◽  
Mean Value ◽  
Ecological Genetics ◽  
Original Population ◽  
Fast Development ◽  
Selection For ◽  
Food Medium

1. Populations of Drosophila melanogaster have been adapted to a new, initially unfavourable diet by adding to the food medium the chelating agent, EDTA, which lowers survival, lengthens development and reduces body size, according to the concentration.2. Six populations were allowed to adapt to the new diet without intervention and compared with two additional populations in which there was either artificial selection for fast development time or in which the effects of variation in development time were minimized and higher egg production was favoured instead.3. All populations adapted successfully and some were able to grow on medium with EDTA concentrations which were lethal for the original population.4. Under uncrowded conditions on EDTA-free medium, in seven out of the eight populations, body size was reduced by about 7% below the level of the original population and the larval period was shorter in several instances. But in the population in which higher egg production was favoured, body size was 7% greater than in the original population and 16% greater than the average of the other EDTA-adapted populations. This contrast was attributed either to intense natural selection for shorter development time or to selection for a higher rate of egg production, which is positively correlated with body size when larvae are grown on sub-optimal conditions.5. Under crowded, competitive conditions, the fitness of the EDTA-adapted and the original populations was reversed according to the presence or absence of EDTA.6. Genetic differences between one of the EDTA-adapted populations and the original population were studied by using marked inversions to interchange chromosome pairs. Larvae of the alternative genotypes were grown on different diets and adaptation was shown to have involved changes in all major chromosomes and also substantial, complementary interaction between non-homologous pairs. Substitution of the third pair of chromosomes from the original Pacific stock in the background of the adapted strain led to complete sterility of females, on all diets tested, and lethality of both sexes at higher levels of EDTA.7. The creation of new equilibria, by manipulating the relative importance of components of fitness, in the course of adaptation to a new environment, offers a valuable technique for studying the selective forces which influence the mean value of quantitative characters generally.

scholarly journals The ecological genetics of growth in Drosophila 4. The influence of larval nutrition on the manifestation of dominance

1961 ◽  
Vol 2 (3) ◽  
pp. 346-360 ◽  
Author(s):  
Forbes W. Robertson
Keyword(s):  
Body Size ◽  
Cell Size ◽  
Large Body ◽  
Ecological Genetics ◽  
Selected Lines ◽  
Pacific Population ◽  
Unselected Population ◽  
Selection For ◽  
Different Strains ◽  
Synthetic Media

(1) Two lines have been selected for small wing cell size from the cage Pacific population. Body size was reduced by about 10% and 15% in the two lines which did not regress when selection was relaxed.(2) The effects of crossing each line to the unselected population has been determined in a number of repeated tests on the live yeast medium and also on various sub-optimal synthetic media.(3) The size of the F1, relative to the size of the parents, is greatly influenced by the composition of the larval diet. The F1 may coincide with the mid-parent value but generally significantly exceeds it and is often the same size as the unselected parent population.(4) In crosses to an unselected population on alternative media the F1 was either the same size as the unselected population or exceeded it.(5) Crosses between the selected lines produced an F1 which exceeded the larger parent but remained well below the level of the unselected population.(6) To test for interaction between genes at different loci, chromosomes from the unselected population were substituted in the genetic background of each of the selected lines to provide an array of genotypes in which one, two or three pairs of major chromosomes had homologues derived from different strains. Leastsquares analysis indicated differences between the lines in the distribution of effects among the chromosomes together with the presence of interaction between chromosomes and this was greater for the substitutions in the line which showed the greater consistency of recessive behaviour in crosses to the unselected population.(7) At the end of the selection experiment two lines were selected for large body size from the F2 of the cross between the two selected lines. Both responded to selection for three to four generations and then fluctuated at a level slightly below that of the unselected population.(8) The physiological changes which involve correlated changes in body and cell size differ from those which result from selection for smaller body size, at least in the early stages of such selection, and are associated with differences in genetic behaviour. The apparently recessive property, which involves extensive non-allelic interaction, is progressively established during the course of selection. Apparently selection for smaller cell size is particularly effective in disturbing the normal homeostasis of growth and is accompanied by relatively greater loss of heterozygosis than is likely with equivalent reduction in size due to selection for smaller body as opposed to cell size.

scholarly journals Atmospheric Hypoxia Limits Selection for Large Body Size in Insects

PLoS ONE ◽  
2009 ◽  
Vol 4 (1) ◽  
pp. e3876 ◽  
Author(s):  
C. Jaco Klok ◽  
Jon F. Harrison
Keyword(s):  
Body Size ◽  
Large Body ◽  
Large Body Size ◽  
Selection For

scholarly journals Selection for reduced fear in red junglefowl changes brain composition and affects fear memory

2020 ◽  
Vol 7 (8) ◽  
pp. 200628
Author(s):  
Rebecca Katajamaa ◽  
Per Jensen
Keyword(s):  
Body Size ◽  
Brain Size ◽  
Prior Experience ◽  
Fear Memory ◽  
Brain Regions ◽  
Preference Learning ◽  
Response To Selection ◽  
Red Junglefowl ◽  
Selection For ◽  
Region Size

Brain size reduction is a common trait in domesticated species when compared to wild conspecifics. This reduction can happen through changes in individual brain regions as a response to selection on specific behaviours. We selected red junglefowl for 10 generations for diverging levels of fear towards humans and measured brain size and composition as well as habituation learning and conditioned place preference learning in young chicks. Brain size relative to body size as well as brainstem region size relative to whole brain size were significantly smaller in chicks selected for low fear of humans compared to chicks selected for high fear of humans. However, when including allometric effects in the model, these differences disappear but a tendency towards larger cerebra in low-fear chickens remains. Low-fear line chicks habituated more effectively to a fearful stimulus with prior experience of that same stimulus, whereas high-fear line chicks with previous experience of the stimulus had a response similar to naive chicks. The phenotypical changes are in line with previously described effects of domestication.

scholarly journals Genetic Changes in Protein, Milk, and Fat Yields as a Response to Selection for Protein Yield in a Closed Population of Holsteins

1990 ◽  
Vol 73 (6) ◽  
pp. 1593-1602 ◽  
Author(s):  
A.J. McAllister ◽  
J.A. Vesely ◽  
T.R. Batra ◽  
A.J. Lee ◽  
C.Y. Lin ◽  
...  
Keyword(s):  
Protein Yield ◽  
Response To Selection ◽  
Genetic Changes ◽  
Closed Population ◽  
Selection For ◽  
Protein Milk

scholarly journals Response to selection for increased pupa weight in Tribolium castaneum as related to population structure

1977 ◽  
Vol 30 (3) ◽  
pp. 237-246 ◽  
Author(s):  
Alan J. Katz ◽  
Franklin D. Enfield
Keyword(s):  
Random Mating ◽  
Selection Response ◽  
Response To Selection ◽  
Short Term ◽  
Selection Systems ◽  
Line Selection ◽  
Selection For ◽  
Seven Generations ◽  
Generation Period ◽  
Term Response

SUMMARYThe effectiveness of selection for increased pupa weight in Tribolium was compared for three different selection systems. In all three systems the same number of breeding individuals was used each generation. Population L was a large random mating population with 24 males and 48 females selected each generation. The C4 and C8 populations were each divided into 6 subpopulations (lines) consisting of 4 males and 8 fem ales. Each of the three populations was replicated. In C4, selection for pupa weight was within lines for three generations, followed by a generation of among-line selection when the best two out of six lines were selected. These lines were then crossed to produce 6 new subpopulations, and the cycle was repeated. The C8 population was handled in exactly the same manner except that seven generations of selection within lines were practised before each generation of among-line selection. Selection response for the 42-generation period was significantly greater in the L population than in either subdivided population. No consistent differences among the selection systems were apparent when evaluating short-term response for the first 12 generations of the experiment. The results were interpreted as indicating that the influence of multiple-peak epistasis was not of major importance for this trait in determining ultimate response to selection when starting from a base population of previously unselected lines and utilizing a within- and among-line selection regime.

scholarly journals The ecological genetics of growth in Drosophila 3. Growth and competitive ability of strains selected on different diets

1960 ◽  
Vol 1 (3) ◽  
pp. 333-350 ◽  
Author(s):  
Forbes W. Robertson
Keyword(s):  
Body Size ◽  
Development Time ◽  
Competitive Ability ◽  
Variable Degree ◽  
Adult Size ◽  
Adverse Conditions ◽  
Low Protein ◽  
Unselected Population ◽  
Selection For ◽  
Live Yeast

1. The growth of strains of Drosophila melanogaster selected for large size under different nutritional conditions has been recorded on a variety of different media and compared with that of the unselected population. The experiments were designed to test the inference from earlier work that selection for the same ‘character’, body size, on different diets leads to more or less different changes in growth and metabolism. The inference has been amply confirmed.2. When compared on a number of deficient synthetic diets, the strains which had been selected either on a low-protein diet or on one in which all the essential nutrients had been reduced, suffered a much smaller reduction in body size than either the unselected population or, especially, a large strain selected on the favourable live yeast medium. Some diets which drastically reduced the body size of the unselected population lead to no change in the size of strains selected on the synthetic media, although development time was prolonged. Hence selection had extended the capacity for maintaining a characteristic adult body size to diets which normally would lead to a decline. This is taken as evidence of improved adaptation to such conditions. There is also some evidence that selection on the synthetic diets had lowered the level of adaptation to the usual live yeast diet, since body size tended to be lower on this medium than on some of the normally sub-optimal diets.3. To provide comparisons in adverse conditions which are probably more closely related to those commonly encountered by populations in nature or the laboratory, the performance of the strains has been compared in a graded series of competitive conditions on the live yeast medium. By using genetically marked files of the foundation population, which were shown to react in the same way as unmarked flies—in terms of survival, body size and development time—the competitive ability of the different strains has been tested against that of unselected individuals. The latter are generally superior to the selected strains, which differ among themselves, however, in a way which can be related to the conditions in which they were selected.4. Under such competitive conditions, the strains selected on the synthetic diets suffer a much greater decline in body size than do the unselected individuals. For the strain selected on live yeast, the proportional reduction of body size is about the same for the unselected flies at lower levels of crowding, but is clearly greater under more severe conditions of competition.5. The low-protein strain has been backcrossed to the unselected stock. When reared on a variety of synthetic diets, the performance of the F1 was generally intermediate between that of the parents.6. Nutritional variation may be responsible for either a high environmental correlation between the two measures of growth, body size and duration of larval period, or no apparent correlation. Provided the diet is not too unfavourable, body size remains constant although development time may be lengthened to a variable degree. With more adverse conditions, body size is reduced and development time is lengthened more or less proportionately. Such differences in reaction probably depend on the particular stage of larval growth and development primarily affected by the treatment; this problem is being examined further. The inverse relations between body size and development time may represent the operation of a kind of safety mechanism which ensures that the adult reproductive state is attained sooner than would be so if the capacity for maintaining a characteristic body size were more effective in relation to deficient diets. Populations and species adapted to different conditions are likely to differ as to where the balance is struck between effective maintenance of a characteristic adult size, with maximum potential egg production, and the alternative response, according to their ecology. This possibility must be borne in mind when the response to selection for, say, body size is compared in different species.

scholarly journals The genetic analysis of the direct and correlated response to selection for chaetae in Drosophila melanogaster

1973 ◽  
Vol 22 (1) ◽  
pp. 1-7
Author(s):  
W. R. Scowcroft
Keyword(s):  
Drosophila Melanogaster ◽  
Genetic Analysis ◽  
Genetic Correlation ◽  
Statistical Approach ◽  
Correlated Response ◽  
Minor Importance ◽  
Response To Selection ◽  
Genetic Changes ◽  
Selection For ◽  
Selection Of

SUMMARYThe direct and correlated response to selection of scutellar microchaetae and scutellar bristles has been analysed by determining the contribution of the three major chromosomes, alone and in combination with each other, to the overall response. The results of the analysis confirm a previous finding, based on a formal statistical approach, that response to selection for microchaetae had highly pleiotropic effects on scutellar bristles. In lines selected, each for high and low microchaetae, genetic changes in the 2nd and 3rd chromosomes are pre-eminent and essentially equal. Inter-chromosomal interactions are of relatively minor importance in interpreting the response to selection for microchaetae but assume greater importance with respect to the correlated character. The results are discussed in terms of the genetic correlation between fitness and the character measured.

scholarly journals Variation of scutellar bristles in Drosophila: XI. Selection for scutellar microchaetae and the correlated response of scutellar bristles

1968 ◽  
Vol 11 (2) ◽  
pp. 125-134 ◽  
Author(s):  
W. R. Scowcroft
Keyword(s):  
Analysis Of Variance ◽  
Genetic Relationship ◽  
Correlated Response ◽  
Response To Selection ◽  
Good Correspondence ◽  
Genetic Changes ◽  
Diallel Crosses ◽  
The Third ◽  
Selection For ◽  
Two Stages

The third chromosome mutant, hairy1, adds a varying number of microchaetae to the scutellum. The genetic relationship between this character and scutellar bristles was investigated using the conventional techniques of full- and half-sib analysis of variance and covariance, direct and correlated response to selection for microchaetae and scutellars respectively and diallel crosses at two stages in the programme. There was a good correspondence between the predicted and realized divergence resulting from selection for increased and decreased microchaetae. The correlated response in scutellar bristles appears to be accounted for primarily by genetic changes in microchaetae.

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