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 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 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 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 Dramatic evolution of body length due to post-embryonic changes in cell size in a newly discovered close relative of C. elegans

2017 ◽  
Author(s):  
Gavin C. Woodruff ◽  
Patrick C. Phillips
Keyword(s):  
Body Size ◽  
Cell Size ◽  
Germ Line ◽  
Large Body ◽  
Developmental Genetics ◽  
Close Relative ◽  
Size Difference ◽  
C Elegans ◽  
Evolutionary Diversification ◽  
Ideal System

AbstractUnderstanding morphological diversity—and morphological constrainto—has been a central question in evolutionary biology since its inception. Nematodes of the genus Caenorhabditis, which contains the well-studied model system C. elegans, display remarkable morphological consistency in the face of extensive genetic divergence. Here, we provide a description of the broad developmental patterns of a recently discovered species, C. sp. 34, which was isolated from fresh figs in Okinawa and which is among the closest known relatives of C. elegans. C. sp. 34 displays an extremely large body size and can grow to be nearly twice as long as C. elegans and all other known members of the genus. Observations of the timing of developmental milestones reveal that C. sp. 34 develops about twice as slowly as C. elegans. Measurements of embryo and larval size show that the size difference between C. sp. 34 and C. elegans is largely due to post-embryonic events, particularly during the transition from larval to adult stages. This difference in size is not attributable to differences in germ line chromosome number or the number of somatic cells. The overall difference in body size is therefore largely attributable to changes in cell size via increased cytoplasmic volume. Because of its close relationship to C. elegans, the distinctness of C. sp. 34 provides an ideal system for the detailed analysis of evolutionary diversification. The context of over forty years of C. elegans developmental genetics also reveals clues into how natural selection and developmental constraint act jointly to promote patterns of morphological stasis and divergence in this group.

scholarly journals SELECTION FOR SMALL AND LARGE BODY SIZE IN THE HOUSE MOUSE

Genetics ◽  
1949 ◽  
Vol 34 (2) ◽  
pp. 194-209
Author(s):  
John W MacArthur
Keyword(s):  
Body Size ◽  
House Mouse ◽  
Large Body ◽  
Large Body Size ◽  
Selection For

scholarly journals FOOD CONSUMPTION, FEED EFFICIENCY, METABOLIC RATE AND UTILIZATION OF GLUCOSE IN LINES OF TRIBOLIUM CASTANEUM SELECTED FOR 21-DAY PUPA WEIGHT

Genetics ◽  
1976 ◽  
Vol 83 (2) ◽  
pp. 393-407 ◽  
Author(s):  
Juan F Medrano ◽  
G A E Gall
Keyword(s):  
Metabolic Rate ◽  
Food Consumption ◽  
Tribolium Castaneum ◽  
Feed Efficiency ◽  
Large Body ◽  
Biological Efficiency ◽  
Growth Stages ◽  
Control Line ◽  
Selected Lines ◽  
Selection For

ABSTRACT Food consumption, feed efficiency, metabolic rate and glucose utilization were studied throughout development in one control (1C) and three selected lines (3, 9, 10) of Tribolium castaneum that had been subjected to long term selection for 21-day pupae weight. Growth rate, body composition, cellular growth and the activity of four dehydrogenase enzymes in the same lines have been reported (Medrano and Gall 1976).—Larva of selected lines consumed 1.2 times as much food as the control and gained an average of 2.9 times as much weight. The rapid growth of the selected lines was associated with a gross feed efficiency 20 to 30% above that for the control line. There was also a small but consistent improvement in the conversion of digested food. Average digestibility was higher for selected lines.—There was little apparent differentiation between the control and selected lines in metabolic rate/individual, but the rate measured on a per-unit weight basis was two- to three-fold greater for the control during the active growth stages. Respiratory quotients (R.Q.) of 1.0, indicative of carbohydrate oxidation, were observed through larval growth in all lines. Pupae at 21 days showed R.Q. values greater than 1.0, which were interpreted as resulting from a phenomenon in insects in which CO2 is released by pupae, in large bursts at irregular intervals. The rate constant of glucose oxidation, measured as the rate of C14 labelled CO2 respired during 2- to 6-hour incubation periods, was two- to three-fold higher in the control. In addition, the control line larvae expired 5% to 17% more of the ingested C14 as CO2. It was apparent that control line individuals maintained a much more active turnover of metabolites but without an effective retention of carbon as body substances. The results are discussed in support of the hypothesis that selection for large body size resulted in improved control mechanisms that influence the biological efficiency of growth in Tribolium.

scholarly journals Effect of Phenotype Selection on Genome Size Variation in Two Species of Diptera

Genes ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 218
Author(s):  
Carl E. Hjelmen ◽  
Jonathan J. Parrott ◽  
Satyam P. Srivastav ◽  
Alexander S. McGuane ◽  
Lisa L. Ellis ◽  
...  
Keyword(s):  
Body Size ◽  
Cell Count ◽  
Genome Size ◽  
Large Body ◽  
Population Variation ◽  
Phenotypic Traits ◽  
Stabilizing Selection ◽  
Large Body Size ◽  
Slow Development ◽  
Selection For

Genome size varies widely across organisms yet has not been found to be related to organismal complexity in eukaryotes. While there is no evidence for a relationship with complexity, there is evidence to suggest that other phenotypic characteristics, such as nucleus size and cell-cycle time, are associated with genome size, body size, and development rate. However, what is unknown is how the selection for divergent phenotypic traits may indirectly affect genome size. Drosophila melanogaster were selected for small and large body size for up to 220 generations, while Cochliomyia macellaria were selected for 32 generations for fast and slow development. Size in D. melanogaster significantly changed in terms of both cell-count and genome size in isolines, but only the cell-count changed in lines which were maintained at larger effective population sizes. Larger genome sizes only occurred in a subset of D. melanogaster isolines originated from flies selected for their large body size. Selection for development time did not change average genome size yet decreased the within-population variation in genome size with increasing generations of selection. This decrease in variation and convergence on a similar mean genome size was not in correspondence with phenotypic variation and suggests stabilizing selection on genome size in laboratory conditions.

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

1961 ◽  
Vol 2 (3) ◽  
pp. 424-430 ◽  
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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