Effect of three types of ecological stress on the variability of morphological traits in Drosophila melanogaster

The effect of temperature, nutrition, and density stresses on phenotypic and genetic variation in morphological traits (thorax length, wing length, number of sternopleural and abdominal bristles, and number of arista branches) was examined in Drosophila melanogaster. In addition, the effect of stress on developmental stability measured as fluctuation asymmetry of bilateral traits was analyzed. All of the stresses were shown to increase phenotypic variation and fluctuating asymmetry of bilateral traits. Genetic variation of morphometric traits estimated using the isofemale line technique was higher under stressful than under normal conditions. Biotic and abiotic stresses were similar in their effect on phenotypic and genetic variation. The effect of stress on variability of morphometric traits was generally higher than on that of meristic traits. Possible causes of the increase of genetic variation under stress are discussed.     

Effects of extreme temperatures on phenotypic variation and developmental stability in Drosophila melanogaster and Drosophila buzzatii

The effect of stressful and nonstressful rearing temperatures on phenotypic variation of four quantitative characters (thorax length, wing length, number of sternopleural chaetae, number of arista branches) and on developmental stability (fluctuating asymmetry) of the three latter characters was estimated in two Drosophila species: Drosophila melanogaster and Drosophila buzzatii . In both species, a general trend for increasing of phenotypic variation and fluctuating asymmetry at stress temperatures was observed; in fluctuating asymmetry, this effect was more pronounced. An increase of phenotypic variation under stress was shown for all characters examined except sternopleural chaeta number in D. buzzatii . Comparison of species responses suggests that the increase of variation in D. melanogaster was somewhat higher than in D. buzzatii .     

Genetic Variability and Fluctuating Asymmetry of Morphological Traits in Drosophila melanogasterReared on a Pesticide-Containing Medium

The effects of chlorine-organic insecticide endosulfane (thiodan) on phenotypic and genetic variation in four morphological traits of Drosophila melanogaster(wing length, thorax length, the number of orbital bristles and the number of sternopleural bristles) were examined. In addition, the effect of this pesticide on stability of development measured as fluctuating asymmetry of bilateral traits was estimated. On the medium with endosulfane, phenotypic variation of morphometric traits was significantly higher. No difference in fluctuating asymmetry between the stressed and the control samples was found. The among-line variance of morphometric traits of flies reared on the endosulfane-containing medium was significantly higher as compared to the corresponding variance under control conditions. The efficiency of using fluctuating asymmetry and phenotypic variation of morphometric and meristic traits as indicators of environmental stress in insect populations is discussed.     

Genetic variability and fluctuating asymmetry of morphological signs of Drosophila melanogaster during development in a pesticide-containing environment

The effects of chlorine-organic insecticide endosulfane (thiodan) on phenotypic and genetic variation in four morphological traits of Drosophila melanogaster (wing length, thorax length, the number of orbital bristles and the number of sternopleural bristles) were examined. In addition, the effect of this pesticide on stability of development measured as fluctuating asymmetry of bilateral traits was estimated. On the medium with endosulfane, phenotypic variation of morphometric traits was significantly higher. No difference in fluctuating asymmetry between the stressed and the control samples was found. The among-line variance of morphometric traits of flies reared on the endosulfane-containing medium was significantly higher as compared to the corresponding variance under control conditions. The efficiency of using fluctuating asymmetry and phenotypic variation of morphometric and meristic traits as indicators of environmental stress in insect populations is discussed.     

Association of single-nucleotide polymorphisms at the Delta locus with genotype by environment interaction for sensory bristle number in drosophila Melanogaster

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.     

Condition dependence and the nature of genetic variation for male sex comb bristle number in <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

Genetic architecture of variation underlying male sex comb bristle number, a rapidly evolving secondary sexual character of Drosophila, was examined. First, in order to test for condition dependence, diet was manipulated in a set of ten Drosophila melanogaster full-sib families. We confirmed heightened condition dependent expression of sex comb bristle number and its female homologue (distal transverse row bristles) as compared to non-sex sternopleural bristles. Significant genotype by environment effects were detected for the sex traits indicating a genetic basis for condition dependence. Next we measured sex comb bristle number and sternopleural bristle number, as well as residual mass, a commonly used condition index, in a set of thirty half-sib families. Sire effect was not significant for sex comb and sternopleural bristle number, and we detected a strong dominance and/or maternal effect or X chromosome effect for both traits. A strong sire effect was detected for condition and its heritability was the highest as compared to sex comb and sternopleural bristles. We discuss our results in light of the rapid response to divergent artificial selection for sex comb bristle number reported previously. The nature of genetic variation for male sex traits continues to be an important unresolved issue in evolutionary biology.     

A potential regulatory polymorphism upstream of hairy is not associated with bristle number variation in wild-caught Drosophila

To extend results from laboratory genetic mapping experiments to natural populations it is necessary to estimate the phenotypic effects attributable to laboratory-identified genetic factors in nature. We retested a polymorphism found to be strongly associated with an increase of 0.35 sternopleural bristles in laboratory strains in two large samples of wild-caught Drosophila melanogaster. Despite >90% power to detect effects as low as 0.27 bristles (<1% of the total variation in bristle number) we did not replicate the association in nature. Potential explanations for this result are explored.     

Misexpression screen in Drosophila melanogaster aiming to reveal novel factors involved in formation of body parts

To identify novel factors that lead a fly imaginal disc to adopt its developmental fate, we carried out a modular dominant misexpression screen in imaginal discs. We have identified two factors that appear to change the fate of the respective body structure and appear to lead to the transformation of a body part. In one mutant line, notum tissue, normally derived from wing imaginal tissue, formed close to the site of the sternopleural bristles, which are leg disc derivatives. In the other line, the arista is transformed into a tubular structure, resembling an abnormal leg. We found that ectopic expression of abrupt was responsible for this potential transformation of the arista.     

The Isolation of Polygenic Factors Controlling Bristle Score in Drosophila Melanogaster. II. Distribution of Third Chromosome Bristle Effects within Chromosome Sections

In the present study an attempt has been made to characterize the genetic ``factors' controlling quantitative characters, bristle numbers, in Drosophila melanogaster. A low sternopleural bristle multiple recessive marker third chromosome was used to analyze a high sternopleural third chromosome, in a high sternopleural bristle background. An attempt was made to estimate the minimum number of ``effective factors' involved in the difference in bristle score between the tested and marker chromosomes. Apart from sternopleural, scutellar and ocellar bristles, a new character, subprimal bristles, was also scored. The unselected characters were used to help in the factor locations, and an attempt made to detect epistasis. Concentrations of bristle effects were found, as were a few `factors' of large effect. At least 17 sternopleural bristle factors are required to account for the difference in bristle score between the high tested third chromosome and the low tester third chromosome. There was an ascertainment problem for polygenes with effects of less than about 0.6 phenotypic standard deviation. Only an estimate of the minimum number of factors and approximate locations can be given with any degree of certainty. The results are compatible with the hypothesis (among others) that quantitative characters are under the control of a few major genes supported by numerous genes with smaller effect.     

Developmental stress in wild-living Drosophilids inferred from biometry: metric and meristic traits react differently to heterogeneous environmental conditions

Abstract.  1. During their development in natural conditions, Drosophila larvae and pupae face heterogeneous environmental conditions (HEC). Analysing the morphology of wild-living adults is a means of evaluating the effects of HEC.
2. Two drosophilid species of the Zaprionus genus that recently invaded the Nile delta were investigated, and three metric, size-related traits, and one meristic trait, the sternopleural bristle number, were measured. Data were compared with those of F₁ generation reared under favourable laboratory conditions.
3. Body size was smaller in nature, but also extremely variable among individuals, with an average coefficient of variation (CV) of 9.1 ± 0.3, against a much lesser value of 2.4 ± 0.1 in laboratory flies. Correlations among size traits were also greater in nature (0.96 ± 0.01) than in the laboratory (0.75 ± 0.04).
4. By contrast, sternopleural bristles produced similar results in wild-living and laboratory flies. In nature, mean numbers were only slightly less than in the laboratory and the CVs were almost identical (10.87 ± 0.70 vs 10.80 ± 0.76).
5. Fluctuating asymmetry of sternopleural bristles was also identical in the two kinds of flies, and was not influenced by HEC, indicating a high level of developmental canalisation with respect to HEC.
6. The implications of the results for the problems of field heritability and developmental stability are discussed.     

Effect of stressful and nonstressful growth temperatures on variation of sternopleural bristle number in Drosophila melanogaster

The effect of stressful (31 degrees C) and nonstressful (25 degrees C) growth temperatures on quantitative variation and developmental stability (fluctuating asymmetry) of Drosophila melanogaster was examined in a short-term selection experiment on sternopleural bristle number. Realized heritabilities based on 10 generations of selection in an upward direction did not differ between the two temperature regimes, which indicated that additive genetic variation was not affected by a high, stressful temperature. Phenotypic variability and fluctuating asymmetry of sternopleural bristles were significantly higher under stressful conditions when averaged over generations, although most pairwise comparisons in separate generations showed nonsignificant differences between temperatures.     

Variability of morphological traits in Drosophila bipectinata complex

Phenotypic or morphological differences among different populations and sexual dimorphism in certain metric traits were analysed in D. bipectinata complex. It was noticed that different populations of D. bipectinata species group harbour large amount of variation for these characters. In all the populations, morphometric characters such as lengths of femur, tibia and wing length, wing width, number of sternopleural bristles and bristles on epandrium varied significantly among populations. The study indicates that the morphological variations are due to the interplay of genetic and environmental endowments. Further, females had significantly larger values, for lengths of femur, tibia and wing length, wing width and sternopleural bristles.     

Variation in Drosophila sensory bristle number at 'Evolution Canyon'

'Evolution Canyon' on Mount Carmel, Israel, displays highly contrasting physical and biotic environments on a micro-geographic scale, and is a natural laboratory for investigating genetic responses to variable and extreme environments across species. Samples of Drosophila melanogaster and D. simulans were collected from three sites each on the north- and south-facing slopes of the canyon along altitudinal transects, and one site on the valley floor. Numbers of abdominal and sternopleural sensory bristles were recorded for each of these subpopulations in three thermal environments. In D. simulans, sternopleural bristle number exhibited micro-geographic differentiation between the north- and south-facing slopes, while abdominal bristle number was stable across subpopulations. In D. melanogaster, the magnitudes of the difference in mean sternopleural bristle number between the north- and south-facing slopes and of mean abdominal bristle number along the altitudinal gradients were both conditional on rearing temperature. Thus, the pattern of genetic variation between sites was consistent with underlying heterogeneity of genetic mechanisms for response to the same environmental gradients between traits and sibling species. In contrast, the genetic architecture of bristle number at the level of variation within populations was very similar between species for the same bristle trait, although the two traits differed in the relative contribution of genotype by temperature and genotype by sex interaction.     

Realized evolvability: quantifying phenotypic evolution in a Drosophila clade

Understanding the evolutionary potential of morphological evolution is still a major problem in evolutionary biology. In this study, we tried to quantify the amount of variation of different traits among species of a Drosophila clade reared under standard conditions. Nineteen different traits have been measured on nine species of the same clade, the Neotropical saltans group of Drosophila. Measured traits can be distributed into five categories: size‐traits (wing and thorax), shape indices (ratios among the size traits), number of sternopleural bristles on the thorax, number of abdominal bristles on successive sternites, and dorsal pigmentation of abdomen. All species are of medium size with a generally dark pigmentation. A remarkable feature is the presence of numerous bristles on the 6th sternite of the males, while this segment is bare in other Drosophila species. A multivariate analysis revealed that it was possible to discriminate all the investigated species by using the complete set of measured traits. For each trait, phenotypic variability was investigated at the within‐ and between‐species levels. As a rule, the interspecific coefficient of variation (CV) was much greater than the within species CV, and it is proposed to call it realized evolvability. All possible correlations were calculated between traits across species, providing many unexpected results. Size traits were highly correlated among them, but not correlated with shape indices. Abdominal traits (bristles and pigmentation) were correlated, but often in opposite directions, with thoracic shape indices. Tergite pigmentation was negatively correlated with bristle number on sternite. For the moment, most of the correlations cannot be explained by developmental processes or parallel selective pressures. Nonetheless, mapping the evolution of the two characters on a molecular phylogeny of the studied species revealed two opposite phylogenetic trends for abdominal pigmentation and setation, respectively. Our data suggest a need for similar studies in other well‐defined Drosophila clades.     

Effect of low stressful temperature on genetic variation of five quantitative traits in Drosophila melanogaster

A half-sib analysis was used to investigate genetic variation for three morphological traits (thorax length, wing length and sternopleural bristle number) and two life-history traits (developmental time and larva-to-adult viability) in Drosophila melanogaster reared at a standard (25 degrees C) and a low stressful (13 degrees C) temperature. Both phenotypic and environmental variation showed a significant increase under stressful conditions in all traits. For estimates of genetic variation, no statistically significant differences were found between the two environments. Narrow heritabilities tended to be higher at 13 degrees C for sternopleural bristle number and viability and at 25 degrees C for wing length and developmental time, whereas thorax length did not show any trend. However, the pattern of genetic variances and evolvability indices (coefficient of genetic variation and evolvability), considered in the context of literature evidence, indicated the possibility of an increase in additive genetic variation for the morphological traits and viability and in nonadditive genetic variation for developmental time. The data suggest that the effect of stressful temperature may be trait-specific and this warns against generalizations about the behaviour of genetic variation under extreme conditions.     

Cellular mechanisms in the development of the Drosophila arista

Epidermal cells of Drosophila form a variety of polarized structures during their differentiation. These polarized structures include epidermal hairs, the shafts of sensory bristles, larval denticles and the arista laterals. The arista is the terminal segment of the antenna and consists of a central core and a series of lateral extensions. Here we describe the cellular mechanisms involved in the development of the arista and the morphogenesis of the laterals. We found that the development of the arista is a complex process that involves coordinated cell shape changes, elongation of the central core, apoptosis, nuclear migration, the formation of polyploid cells and the outgrowth of the laterals. This developmental program is highly conserved in the development of the arista in the housefly (Musca domestica). Altering arista cell number in Drosophila by stimulating or inhibiting apoptosis results in an altered number of laterals. Interestingly, the increased number of laterals that result from the inhibition of apoptosis in Drosophila results in an arista whose morphology is reminiscent of the Musca arista. Previous experiments have shown that both the actin and microtubule cytoskeletons have important functions in the cellular morphogenesis of hairs and bristles. Inhibitor studies reported here show that this is also the case for the formation of the arista laterals, arguing that the actin and microtubule cytoskeletons have similar functions in the morphogenesis of all of these cell types. We conclude that the arista laterals are a valuable complementary cell type system for studying the morphogenesis of polarized cellular extensions in Drosophila.     

Phenotypic variability of quantitative traits in Indian populations of Drosophila kikkawai

Drosophila kikkawai, which has colonized the Indian subcontinent in the recent past, exhibits geographical variations for five quantitative traits among eight Indian populations (8.29–32.7°N). Body weight, wing length, thorax length, abdominal bristles and ovariole number exhibit significant clinal variation with increase in latitude, while sternopleural bristles do not demonstrate such a trend. For the female sex, the slope values for body weight (2.25) and wing length (2.40) are higher but they are lower for thorax length (0.64) and ovariole number (0.51 per degree latitude). There is significant sexual dimorphism for the slope values only for body weight and thorax length suggesting simultaneous action of latitudinal selection pressure on these traits. However, the two sexes do not differ statistically in the latitudinal slope values for the wing length. A regression analysis of different traits on body weight implies correlated selection response on wing length and wing/thorax ratio while thorax length corresponds to changes in body size and does not differ in the two sexes. Regression analysis, on the basis of temperature-related climatic variables, evidence significantly higher association between all the five size-related traits and coefficient of variation of mean annual temperature (seasonal thermal amplitude; T _cv), T _min and relative humidity. Thus, genetic differentiation for quantitative traits in D. kikkawai are due to selective pressure from variable climatic conditions occurring on the Indian subcontinent.     

灯盏花种质资源群体表型多样性研究

以采集自云南和贵州的21份灯盏花种质资源为材料,观测了它们的群体表型性状特征,并分析了这些表型性状的遗传多样性.结果表明:灯盏花种质资源的表型质量性状在居群内外均有丰富变异,不同质量性状的频率不同,并以多叶型的植株、绿色的茎、疏的茎毛、倒披针型的基生叶、全缘叶、锐尖的叶尖、花色淡紫和黄色的管状花冠口等为代表性表型性状.居群内各数量性状间以单株基生叶数和单株分枝数变异系数较高(均超过50%),而花序直径变异系数最低(18.14%);居群间各表型性状以株高和单序管状花数变异系数较高(52.98%和41.98%),而单株基生叶数和基生叶长变异系数较低(<20%).地理类群间表型分化系数为26.58%,地理类群内表型分化系数为73.42%.灯盏花性状表型多样性指数以株高最高(2.243),以单株分枝数和单株基生叶数较低(1.723和1.874),总体平均表型多样性指数为2.028;不同地理类群的表型多样性指数为1.589~1.890,并以楚雄地区最高,曲靖地区最低.研究发现,灯盏花种质资源具有丰富的质量和数量性状变异,多数性状的地理类群内变异大于地理类群间,且表型多样性指数相对较高,对其地理类群内变异的保护和利用对灯盏花育种具有重要的意义.     

A test of quantitative genetic theory using Drosophila- effects of inbreeding and rate of inbreeding on heritabilities and variance components

Inbreeding is expected to decrease the heritability within populations. However, results from empirical studies are inconclusive. In this study, we investigated the effects of three breeding treatments (fast and slow rate of inbreeding - inbred to the same absolute level - and a control) on heritability, phenotypic, genetic and environmental variances of sternopleural bristle number in Drosophila melanogaster. Heritability, and phenotypic, genetic and environmental variances were estimated in 10 replicate lines within each of the three treatments. Standard least squares regression models and Bayesian methods were used to analyse the data. Heritability and additive genetic variance within lines were higher in the control compared with both inbreeding treatments. Heritabilities and additive genetic variances within lines were higher in slow compared with fast inbred lines, indicating that slow inbred lines retain more evolutionary potential despite the same expected absolute level of inbreeding. The between line variance was larger with inbreeding and more than twice as large in the fast than in the slow inbred lines. The different pattern of redistribution of genetic variance within and between lines in the two inbred treatments cannot be explained invoking the standard model based on selective neutrality and additive gene action. Environmental variances were higher with inbreeding, and more so with fast inbreeding, indicating that inbreeding and the rate of inbreeding affect environmental sensitivity. The phenotypic variance decreased with inbreeding, but was not affected by the rate of inbreeding. No inbreeding depression for mean sternopleural bristle number was observed in this study. Considerable variance between lines in additive genetic variance within lines was observed, illustrating between line variation in evolutionary potential.     

The isolation of polygenic factors controlling bristle score in Drosophila melanogaster. I. Allocation of third chromosome sternopleural bristle effects to chromosome sections

A single third chromosome C, with a high sternopleural bristle score, had been extracted from an artificial selection line. C was divided into five chromosomal sections by recombination with a multiply marked third chromosome ruseca, which had a low sternopleural bristle score. A nonuniform distribution of sternopleural bristle effect with physical length of chromosome was observed. The second section (26-44 cM) of C carried the most sternopleural bristle effect (10 bristles when homozygous), the first (0-26 cM) and third (44-62 cM) also carried significant sternopleural bristle effects (six and five bristles, respectively). The fourth section (62-71 cM) carried a small but significant effect (less than one bristle) while the fifth section (71-101 cM) carried little effect when alone (less than one bristle), though it did carry effects which had an epistatic interaction with those of the first and second sections.