scholarly journals Polygenic mutation in Drosophila melanogaster: the causal relationship of bristle number to fitness.

Genetics ◽  
1995 ◽  
Vol 139 (2) ◽  
pp. 861-872 ◽  
Author(s):  
S V Nuzhdin ◽  
J D Fry ◽  
T F Mackay
Keyword(s):  
Drosophila Melanogaster ◽  
Artificial Selection ◽  
Random Mating ◽  
Direct Selection ◽  
Stabilizing Selection ◽  
Fitness Effects ◽  
Bristle Number ◽  
Mean Fitness ◽  
The Mean ◽  
Average Fitness

Abstract The association between sternopleural and abdominal bristle number and fitness in Drosophila melanogaster was determined for sublines of an initially highly inbred strain that were maintained by divergent artificial selection for 150 generations or by random mating for 180 generations. Replicate selection lines had more extreme bristle numbers than those that were maintained without artificial selection at the same census size for approximately the same number of generations. The average fitness, estimated by a single generation of competition against a compound autosome strain, was 0.17 for lines selected for high and low abdominal bristle numbers and 0.19 for lines selected for high and low sternopleural bristle number. The average fitness of unselected lines, 0.46, was significantly higher than that of the selection lines. The fitnesses and the relationships of bristle number to fitness in progeny of all possible crosses of high x high (H x H), high x low (H x L) and low x low (L x L) selection lines were examined to determine whether the observed intermediate optima were caused by direct stabilizing selection on bristle number or by apparent stabilizing selection mediated through deleterious pleiotropic fitness effects of mutations affecting bristle number. Although bristle number was nearly additive for progeny of H x H, H x L and L x L crosses among sternopleural bristle selection lines, their mean fitnesses were not significantly different from each other, or from the mean fitness of the unselected lines, suggesting partly or completely recessive pleiotropic fitness effects cause apparent stabilizing selection. The average fitness of the progeny of H x H abdominal bristle selection lines was not significantly different from the fitness of unselected lines, but the mean fitness of the progeny of L x L crosses was not significantly different from that of the pure low lines. This is consistent with direct selection against low but not high abdominal bristle number, but the interpretation is confounded by variation in average degree of dominance for fitness (on average recessive in the high abdominal bristle selection lines and additive in the low abdominal bristle selection lines). Neither direct stabilizing selection nor pleiotropy, therefore, can account for all the observations.

scholarly journals GENETIC LOAD IN NATURAL POPULATIONS: IS IT COMPATIBLE WITH THE HYPOTHESIS THAT MANY POLYMORPHISMS ARE MAINTAINED BY NATURAL SELECTION?

Genetics ◽  
1974 ◽  
Vol 77 (3) ◽  
pp. 569-589
Author(s):  
Martin L Tracey ◽  
Francisco J Ayala
Keyword(s):  
Drosophila Melanogaster ◽  
Natural Selection ◽  
Natural Population ◽  
Natural Populations ◽  
Genetic Load ◽  
Structural Genes ◽  
Invertebrate Species ◽  
Average Proportion ◽  
Mean Fitness ◽  
The Mean

ABSTRACT Recent studies of genetically controlled enzyme variation lead to an estimation that at least 30 to 60% of the structural genes are polymorphic in natural populations of many vertebrate and invertebrate species. Some authors have argued that a substantial proportion of these polymorphisms cannot be maintained by natural selection because this would result in an unbearable genetic load. If many polymorphisms are maintained by heterotic natural selection, individuals with much greater than average proportion of homozygous loci should have very low fitness. We have measured in Drosophila melanogaster the fitness of flies homozygous for a complete chromosome relative to normal wild flies. A total of 37 chromosomes from a natural population have been tested using 92 experimental populations. The mean fitness of homozygous flies is 0.12 for second chromosomes, and 0.13 for third chromosomes. These estimates are compatible with the hypothesis that many (more than one thousand) loci are maintained by heterotic selection in natural populations of D. melanogaster.

scholarly journals Complex constraints on allometry revealed by artificial selection on the wing of Drosophila melanogaster

2015 ◽  
Vol 112 (43) ◽  
pp. 13284-13289 ◽  
Author(s):  
Geir H. Bolstad ◽  
Jason A. Cassara ◽  
Eladio Márquez ◽  
Thomas F. Hansen ◽  
Kim van der Linde ◽  
...  
Keyword(s):  
Drosophila Melanogaster ◽  
Artificial Selection ◽  
Allometric Scaling ◽  
Power Laws ◽  
Selection Response ◽  
Wing Shape ◽  
Fundamental Aspect ◽  
Direct Selection ◽  
Evolutionary Potential ◽  
Internal Selection

Precise exponential scaling with size is a fundamental aspect of phenotypic variation. These allometric power laws are often invariant across taxa and have long been hypothesized to reflect developmental constraints. Here we test this hypothesis by investigating the evolutionary potential of an allometric scaling relationship in drosophilid wing shape that is nearly invariant across 111 species separated by at least 50 million years of evolution. In only 26 generations of artificial selection in a population of Drosophila melanogaster, we were able to drive the allometric slope to the outer range of those found among the 111 sampled species. This response was rapidly lost when selection was suspended. Only a small proportion of this reversal could be explained by breakup of linkage disequilibrium, and direct selection on wing shape is also unlikely to explain the reversal, because the more divergent wing shapes produced by selection on the allometric intercept did not revert. We hypothesize that the reversal was instead caused by internal selection arising from pleiotropic links to unknown traits. Our results also suggest that the observed selection response in the allometric slope was due to a component expressed late in larval development and that variation in earlier development did not respond to selection. Together, these results are consistent with a role for pleiotropic constraints in explaining the remarkable evolutionary stability of allometric scaling.

scholarly journals A quantitative genetic analysis of fitness and its components in Drosophila melanogaster

1986 ◽  
Vol 47 (1) ◽  
pp. 59-70 ◽  
Author(s):  
Trudy F. C. Mackay
Keyword(s):  
Drosophila Melanogaster ◽  
Natural Populations ◽  
Strongly Correlated ◽  
Wild Type ◽  
Relative Contribution ◽  
Quantitative Characters ◽  
Quantitative Genetic ◽  
Bristle Number ◽  
Metric Traits ◽  
Average Fitness

SummaryForty-one third chromosomes extracted from a natural population of Drosophila melanogaster were assessed for net fitness and for the quantitative characters viability, net fertility, female productivity, male weight, abdominal bristle number, and sternopleural bristle number. Net homozygous and heterozygous fitness of the third chromosomes was estimated by competition against a marked balancer third chromosome. Average fitness of the homozygous lines relative to wild-type heterozygotes was 0·13, indicating substantial inbreeding depression for net fitness. All significant correlations of quantitative characters with fitness and with each other were high and positive. Homozygous fitness is strongly correlated with net fertility, viability, and female productivity, moderately associated with male weight, and not significantly associated with bristle traits. The combination of metric traits which best predicts homozygous fitness is the simple multiple of viability and female productivity. Heterozygous fitness is not correlated with homozygous fitness; furthermore, the relative contribution of metric traits to fitness in a heterozygous population is likely to be different from that deduced from homozygous lines. These observations are consistent with a model of genetic variation for fitness in natural populations caused by segregation of rare deleterious recessive alleles.

scholarly journals STABILIZING SELECTION DETECTED FOR BRISTLE NUMBER IN DROSOPHILA MELANOGASTER

Evolution ◽  
1996 ◽  
Vol 50 (4) ◽  
pp. 1573-1578 ◽  
Author(s):  
Aurora García-Dorado ◽  
Jorge A. González
Keyword(s):  
Drosophila Melanogaster ◽  
Stabilizing Selection ◽  
Bristle Number

scholarly journals Effects of Artificial Selection on Rates of Inbreeding in Populations of Drosophila Melanogaster

1969 ◽  
Vol 22 (1) ◽  
pp. 143 ◽  
Author(s):  
LP Jones
Keyword(s):  
Drosophila Melanogaster ◽  
Artificial Selection ◽  
Bristle Number ◽  
Seven Generations

The rate of inbreeding was studied using the conventional F value, as well as the "percentage of genes" technique of James and McBride (1958), in lines of D. melanogaster selected for increased abdominal bristle number for seven generations at intensities of 10, 20, and 50% with 10 pairs of parents.

scholarly journals The time of detection of recessive visible genes in small populations

1978 ◽  
Vol 31 (3) ◽  
pp. 255-264 ◽  
Author(s):  
Alan Robertson
Keyword(s):  
Artificial Selection ◽  
Finite Population ◽  
Random Mating ◽  
Recessive Gene ◽  
New Mutation ◽  
Mating Population ◽  
Initial Generation ◽  
The Mean ◽  
Time To Detection ◽  
Mean Time

SUMMARYHomozygotes for recessive visible genes have often been discovered in lines under artificial selection, sometimes many generations from the start. As a help in the interpretation of this phenomenon, the distribution of the time to first detection as a homozygote of a recessive gene occurring only once in the initial generation has been obtained. Alternatively the results may be considered as referring to the time of first appearance as a homozygote of a new mutation occurring in a finite population. For a monoecious random mating population of size N with selfing permitted, the mean time to detection is very close to 2N⅓ over a range of N from 1 to 500 with a coefficient of variation of roughly 2/3 and a 95% upper limit about 2·5 times the mean. If selfing is prohibited, the mean time is increased by a little over 1 generation. The treatment is extended to cover the effects of artificial selection in favour of the heterozygote, of the frequency of occurrence in the initial generation and of the examination of more individuals each generation than are used as parents.

Dominance, allele frequency and selection in a population of Drosophila melanogaster

1980 ◽  
Vol 208 (1171) ◽  
pp. 163-187 ◽  
Keyword(s):  
Drosophila Melanogaster ◽  
Regression Line ◽  
Inbred Lines ◽  
Negative Slope ◽  
Stabilizing Selection ◽  
Recurrent Parent ◽  
Single Pair ◽  
Two Temperatures ◽  
The Mean ◽  
Half Diallel

The numbers of sternopleural chaetae of 18 inbred lines derived from the Texas population of Drosophila melanogaster were ascertained for flies raised at each of two temperatures, 18 and 25°C. Two characters were then defined: M , the average of the chaeta numbers at the two tempera­tures; and S , half of the difference between the average chaeta numbers at the two temperatures. The inbred lines differed among themselves in both characters, so revealing genetic variation in the Texas population for them both. There was no correlation between the values of M and S among the lines. The mean of the inbred lines did not differ significantly from that of the progenies of 22 single-pair matings among flies taken from the population in either character, so suggesting that the 18 inbred lines provided a fair sample of the genes in the population. The differ­ences between the variances among the inbred lines, on the one hand, and the biparental progenies, on the other, suggested that dominance was present for both characters and that dominant alleles were, in general, present at higher frequencies than their recessive fellows. This was confirmed by a half-diallel experiment with 11 of the 18 inbred lines as parents. The half-diallel further showed that dominance was ambidirectional for character S , but gave no conclusive evidence in this respect for M . The theoretical consequences of ambidirectional dominance combined with higher frequencies of dominant alleles were considered for a simple model involving four loci. This showed, in particular, that when one homozygous line (the recurrent parent) is crossed to a number of other lines (the non-recurrent parents), the amount by which the phenotype of the F 1 exceeds the mean of its two parents shows a regres­sion of negative slope on the phenotype of the non-recurrent parent. The regression line is expected to cut the axis of zero excess at a point that is, on average, as far away from the phenotype of maximum dominance as is the expression of the character in the recurrent parent, but in the opposite direction. The point mid-way between the recurrent parent and the inter­cept thus provides an estimate of the phenotype of maximum dominance. Estimates of the phenotypes of maximum dominance were obtained in this way for both characters, M and S , by means of data from the half-diallel and from a further experiment carried out for the purpose. For character M , the phenotype of maximum dominance does not depart significantly from the mean of the inbreds or from that of the Texas population itself; but, for S , though close to the means, it is significantly higher than them. It is concluded that this type of genetical architecture is to be expected with characters under stabilizing selection and that the phenotype of maximum dominance is the optimal phenotype towards which the selection has been acting.

Stabilizing Selection Detected for Bristle Number in Drosophila melanogaster

Evolution ◽  
1996 ◽  
Vol 50 (4) ◽  
pp. 1573 ◽  
Author(s):  
Aurora Garcia-dorado ◽  
Jorge A. Gonzalez
Keyword(s):  
Drosophila Melanogaster ◽  
Stabilizing Selection ◽  
Bristle Number

scholarly journals Polygenic mutation in Drosophila melanogaster: estimates from response to selection of inbred strains.

Genetics ◽  
1994 ◽  
Vol 136 (3) ◽  
pp. 937-951 ◽  
Author(s):  
T F Mackay ◽  
J D Fry ◽  
R F Lyman ◽  
S V Nuzhdin
Keyword(s):  
Drosophila Melanogaster ◽  
Artificial Selection ◽  
Inbred Strains ◽  
Response To Selection ◽  
Environmental Variance ◽  
Rapid Responses ◽  
Bristle Number ◽  
Mutational Variance ◽  
Selection Of ◽  
New Mutations

Abstract Replicated divergent artificial selection for abdominal and sternopleural bristle number from a highly inbred strain of Drosophila melanogaster resulted in an average divergence after 125 generations of selection of 12.0 abdominal and 8.2 sternopleural bristles from the accumulation of new mutations affecting bristle number. Responses to selection were highly asymmetrical, with greater responses for low abdominal and high sternopleural bristle numbers. Estimates of VM, the mutational variance arising per generation, based on the infinitesimal model and averaged over the responses to the first 25 generations of selection, were 4.32 x 10(-3) VE for abdominal bristle number and 3.66 x 10(-3) VE for sternopleural bristle number, where VE is the environmental variance. Based on 10 generations of divergent selection within lines from generation 93, VM for abdominal bristle number was 6.75 x 10(-3) VE and for sternopleural bristle number was 5.31 x 10(-3) VE. However, estimates of VM using the entire 125 generations of response to selection were lower and generally did not fit the infinitesimal model largely because the observed decelerating responses were not compatible with the predicted increasing genetic variance over time. These decelerating responses, periods of response in the opposite direction to artificial selection, and rapid responses to reverse selection all suggest new mutations affecting bristle number on average have deleterious effects on fitness. Commonly observed periods of accelerated responses followed by long periods of stasis suggest a leptokurtic distribution of mutational effects for bristles.

scholarly journals Association of single-nucleotide polymorphisms at the Delta locus with genotype by environment interaction for sensory bristle number in Drosophila melanogaster

2002 ◽  
Vol 79 (3) ◽  
pp. 211-218 ◽  
Author(s):  
GRETCHEN L. GEIGER-THORNSBERRY ◽  
TRUDY F. C. MACKAY
Keyword(s):  
Standard Deviation ◽  
Single Nucleotide Polymorphisms ◽  
Genotype By Environment Interaction ◽  
Stabilizing Selection ◽  
Environment Interaction ◽  
Nucleotide Polymorphisms ◽  
Single Nucleotide ◽  
Genotype By Environment ◽  
Bristle Number ◽  
The Mean

The nature of forces maintaining variation for quantitative traits can only be assessed at the level of individual genes affecting variation in the traits. Identification of single-nucleotide polymorphisms (SNPs) associated with variation in Drosophila sensory bristle number at the Delta (Dl) locus provides us with the opportunity to test a model for the maintenance of variation in bristle number by genotype by environment interaction (GEI). Under this model, genetic variation is maintained at a locus under stabilizing selection if phenotypic values of heterozygotes are more stable than homozygotes across a range of environments, and the mean allelic effect is much smaller than the standard deviation of allelic effects across environments. Homozygotes and heterozygotes for two SNPs at Dl, one affecting sternopleural and the other abdominal bristle number, were reared in five different environments. There was significant GEI for both bristle traits. Neither condition of the model was satisfied for Dl SNPs exhibiting GEI for sternopleural bristle number. Heterozygotes for the abdominal bristle number SNPs were indeed the most stable genotype for two of the three environment pairs exhibiting GEI, but the mean genotypic effect was greater than the standard deviation of effects across environments. Therefore, this mechanism of GEI seems unlikely to be responsible for maintaining the common bristle number polymorphisms at Dl.

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