Abdominal pigmentation in Drosophila melanogaster females from natural Indian populations

Females of Drosophila melanogaster collected from five geographically distant populations in India were analysed for the intensity of pigmentation in the 5th, 6th and 7th segments of the abdomen. In all three segments, this intensity was found to vary among individuals of any given population, and, furthermore, different populations differ with respect to this phenotypic trait. Statistical analysis revealed significant intra- and interpopulational variation. A clinical pattern was detected: females from populations closer to the equator tended to have lighter cuticle, in which case differences between the three segments could not be detected and all three segments responded both independently and jointly to latitudinal variation, as indicated by a statistically significant positive correlation between latitude and pigmentation score. This is the first report on abdominal pigmentation analysis in natural populations of D. melanogaster that provides evidence that phenotypic flexibility reflects temperature differences, as a result of which abdominal pigmentation shows geographic differentiation.     

Phenotypic variability of thoracic pigmentation in Indian populations of Drosophila melanogaster

Fourteen natural populations of Drosophila melanogaster collected along diverse latitudinal and altitudinal ranges, were analysed for thoracic trident pigmentation at two different breeding temperatures (17 and 25°C) for both sexes. Statistical analyses showed significant intra- as well as interpopulational genetic variations. Clinal patterns for thoracic trident pigmentation along latitude as well as altitude are significantly correlated with thermal amplitude ( T _cv). Crosses between dark (Shimla) and light (Kalka) variants of trident pigmentation produced intermediate phenotypes, and a clear maternal effect was observed in the reciprocal F ₁ crosses. Data suggest that the temperature differences have resulted in phenotypic plasticity of thoracic pigmentation across the Indian subcontinent.     

Genetic basis of natural variation in body pigmentation in Drosophila melanogaster

Body pigmentation in insects and other organisms is typically variable within and between species and is often associated with fitness. Regulatory variants with large effects at bab1, t and e affect variation in abdominal pigmentation in several populations of Drosophila melanogaster. Recently, we performed a genome wide association (GWA) analysis of variation in abdominal pigmentation using the inbred, sequenced lines of the Drosophila Genetic Reference Panel (DGRP). We confirmed the large effects of regulatory variants in bab1, t and e; identified 81 additional candidate genes; and validated 17 candidate genes (out of 28 tested) using RNAi knockdown of gene expression and mutant alleles. However, these analyses are imperfect proxies for the effects of segregating variants. Here, we describe the results of an extreme quantitative trait locus (xQTL) GWA analysis of female body pigmentation in an outbred population derived from light and dark DGRP lines. We replicated the effects on pigmentation of 28 genes implicated by the DGRP GWA study, including bab1, t and e and 7 genes previously validated by RNAi and/or mutant analyses. We also identified many additional loci. The genetic architecture of Drosophila pigmentation is complex, with a few major genes and many other loci with smaller effects.     

Evidence of gene conversion associated with a selective sweep in Drosophila melanogaster

Since Drosophila melanogaster colonized Europe from tropical Africa 10 to 15 thousand years ago, it is expected that adaptation has played a major role in this species in recent times. A previously conducted multilocus scan of noncoding DNA sequences on the X chromosome in an ancestral and a derived population of D. melanogaster revealed that some loci have been affected by directional selection in the European population. We investigated if the pattern of DNA sequence polymorphism in a region surrounding one of these loci can be explained by a hitchhiking event. We found strong evidence that the studied region around the gene unc-119 was shaped by a recent selective sweep, including a valley of reduced heterozygosity of 83.4 kb, a skew in the frequency spectrum, and significant linkage disequilibrium on one side of the valley. This region, however, was interrupted by gene conversion events leading to a strong haplotype structure in the center of the valley of reduced variation.     

Divergent enhancer haplotype of ebony on inversion In(3R)Payne associated with pigmentation variation in a tropical population of Drosophila melanogaster

The pattern and intensity of pigmentation have direct impact on individual fitness through various ecological factors. In a Drosophila melanogaster population from southern Japan, thoracic trident pigmentation intensity of most of the strains could be classified into Dark or Light‐type. The expression level variation of the ebony gene correlated well with this phenotype and the allelic differences in expression indicated that the variation is partly due to cis‐regulatory changes. In the ～13 kb gene region, we identified 17 nucleotide sites and 2 indels that were in complete association with the thoracic trident pigmentation intensity. Interestingly, 11 out of 19 sites located within ～0.5 kb of the core epidermis enhancer. These sites had no obvious association with the abdominal pigmentation intensity in the previously analysed African populations from Uganda and Kenya, which suggested that multiple potential mutational pathways in the cis‐regulatory control region of a single gene could lead to similar phenotypic variation within this species. We also found that the Light‐type enhancer haplotype is strongly linked to a cosmopolitan inversion, In(3R)Payne, which is predominant in warmer climatic regions in both hemispheres. The sequence pattern suggested that the strong linkage may be due to selective forces related to thermal adaptation. The inferred selection for lighter pigmentation in the Japanese population is in the opposite direction of the previously reported case of selection for darker individuals in African populations. Nevertheless, both adaptive changes involved cis‐regulatory changes of ebony, which shows that this gene is likely to be a common target of natural selection.     

黑腹果蝇黑条体突变体的求偶行为

黑腹果蝇Drosophila melanogaster黑条体果蝇(e^bsr)与黑檀体果蝇(e)为同一个基因(ebony)的不同突变体, 两者具有相似的形态表型, 但行为特征表现出明显的差异。本研究以黑条体、 黑檀体和野生型果蝇为研究对象, 首先检测果蝇的视力和活跃度, 再采用不同交配组合进行求偶成功率、交配时间和求偶模式的分析。结果表明: 黑条体果蝇视力与活跃度与野生型果蝇比较无显著差异; 黑条体果蝇的交配成功率和交配潜伏期与野生型果蝇不存在显著的差异; 黑檀体果蝇的交配成功率和交配潜伏期与野生型果蝇存在极显著的差异（P<0.000）。黑条体果蝇表现出异于黑檀体果蝇的活跃度和交配活力, 可能是由于黑条体果蝇ebony基因的新突变导致了果蝇体内多巴胺水平异常, 从而形成了黑条体果蝇独特的求偶模式。     

The molecular genetics of clinal variation: a case study of ebony and thoracic trident pigmentation in Drosophila melanogaster from eastern Australia

Widespread pigmentation diversity coupled with a well‐defined genetic system of melanin synthesis and patterning in Drosophila provides an excellent opportunity to study phenotypes undergoing evolutionary change. Pigmentation variation is highly correlated with different ecological variables and is thought to reflect adaptations to different environments. Several studies have linked candidate genes from Drosophila melanogaster to intra‐population variation and interspecific morphological divergence, but less clearly to variation among populations forming pigmentation clines. We characterized a new thoracic trident pigmentation cline in D. melanogaster populations from eastern Australia, and applied a candidate gene approach to explain the majority of the geographically structured phenotypic variation. More melanized populations from higher latitudes tended to express less ebony than their tropical counterparts, and an independent artificial selection experiment confirmed this association. By partitioning temperature dependent effects, we showed that the genetic differences underlying clinal patterns for trident variation at 25 °C do not explain the patterns observed at 16 °C. Changes in thoracic trident pigmentation could be a common evolutionary response to climatically mediated environmental pressures. On the Australian east coast most of the changes appear to be associated with regulatory divergence of the ebony gene but this depends on temperature.     

Genetic basis of natural variation in body pigmentation in Drosophila melanogaster

Body pigmentation in insects and other organisms is typically variable within and between species and is often associated with fitness. Regulatory variants with large effects at bab1, t and e affect variation in abdominal pigmentation in several populations of Drosophila melanogaster. Recently, we performed a genome wide association (GWA) analysis of variation in abdominal pigmentation using the inbred, sequenced lines of the Drosophila Genetic Reference Panel (DGRP). We confirmed the large effects of regulatory variants in bab1, t and e; identified 81 additional candidate genes; and validated 17 candidate genes (out of 28 tested) using RNAi knockdown of gene expression and mutant alleles. However, these analyses are imperfect proxies for the effects of segregating variants. Here, we describe the results of an extreme quantitative trait locus (xQTL) GWA analysis of female body pigmentation in an outbred population derived from light and dark DGRP lines. We replicated the effects on pigmentation of 28 genes implicated by the DGRP GWA study, including bab1, t and e and 7 genes previously validated by RNAi and/or mutant analyses. We also identified many additional loci. The genetic architecture of Drosophila pigmentation is complex, with a few major genes and many other loci with smaller effects.     

生活中潜在诱变剂对果蝇存活率及遗传变异的影响

用紫外线、抗氧化剂、化妆品等多种生活中潜在的诱变剂处理野生型黑腹果蝇,观察果蝇的存活率及性状遗传变异情况,进而分析这些诱变剂对于果蝇的影响。实验结果表明,随紫外线照射时间的增加,果蝇生活力降低,子代果蝇突变率增加;随培养基中抗氧化剂浓度的增加,果蝇突变率与死亡率均呈上升趋势;不同化妆品也对果蝇造成了明显伤害,造成亲代个体死亡,后代出现突变型果蝇。     

Inferring the effects of demography and selection on Drosophila melanogaster populations from a chromosome-wide scan of DNA variation

Identifying regions of the Drosophila melanogaster genome that have been recent targets of positive Darwinian selection will provide evidence for adaptations that have helped this species to colonize temperate habitats. We have begun a search for such genomic regions by analyzing multiple loci (about 250) dispersed across the X chromosome in a putatively ancestral population from East Africa and a derived European population. For both populations we found evidence for past changes in population size. We estimated that a major bottleneck associated with the colonization of Europe occurred about 3,500-16,000 years ago. We also found that while this bottleneck can account for most of the reduction in variation observed in the European sample, there is a deficit of polymorphism in some genomic regions that cannot be explained by demography alone.     

Rapid loss of stress resistance in Drosophila melanogaster under adaptation to laboratory culture

We investigate changes in resistance to desiccation and starvation during adaptation of Drosophila melanogaster to laboratory culture. We test the hypothesis that resistance to environmental stresses is lost under laboratory adaptation. For both traits, there was a rapid loss of resistance over a three-year period. The rapidity of the response suggested that mutation accumulation could not account for it. Rather, resistance to environmental stresses appeared to be lost as a correlated response to selection on another trait, such as early fertility, with which stress resistance is negatively genetically correlated. These results suggest that caution is needed when extrapolating from evolution of stress resistance in long-established laboratory stocks to patterns of responses and correlated responses in natural populations.     

Thermal adaptive significance of ADH and EST-6 allozymes in Indian geographical populations of Drosophila melanogaster

Indian geographical populations of Drosophila melanogaster exhibit significant correlation (r 0.95) of allelic frequencies at Est -6 and Adh loci with latitude as well as altitude. Est -6^S and AdhF allozymes are well adapted to colder environments while Est -6^F and AdhS are warm adapted. The data on allozymic clines match climatic conditions on the Indian subcontinent. On the basis of multiple regression analysis, one major conclusion is that coefficient of variation of temperature ( T _CV) along latitude/altitude accounts for alterations in allelic frequency at the Adh locus while T _max and T _max explain changes at the Est -6 locus. Thus, climatic conditions lead to thermal selection of allozymes in Indian populations of D. melanogaster .     

Abdominal pigmentation and growth temperature in Indian Drosophila melanogaster: Evidence for genotype-environment interaction

Phenotypic variability for abdominal pigmentation in females of an Indian natural population ofDrosophila melanogaster was studied using isofemale lines and by rearing the larvae and pupae at 4 different temperatures ranging from 20–30°C. The dark pigmented area was found to increase in all the three segments when the growth temperature decreases. A significant positive correlation was detected for the occurrence of dark pigmentation in the 5th and 6th segments in each growth temperature but for other comparisons the correlation was not regular. Analysis of variance (ANOVA) was carried out both for individual segments over different growth temperatures and also for each temperature over the three abdominal segments and in all cases found to be statistically significant. The results are quite different from the earlier observation in FrenchDrosophila melanogaster and suggest that genes controlling pigmentation are temperature dependent; temperature could affect post-transitional events involved in pigmentation. The present findings also clearly indicate that significant genotype-environment interaction exists, responsible for the production of desired phenotype at the opportune moment during the life span of a species.     

No evidence of mitochondrial genetic variation for sperm competition within a population of Drosophila melanogaster

Recent studies have advocated a role for mitochondrial DNA (mtDNA) in sperm competition. This is controversial because earlier theory and empirical work suggested that mitochondrial genetic variation for fitness is low. Yet, such studies dealt only with females and did not consider that variation that is neutral when expressed in females, might be non-neutral in males as, in most species, mtDNA is never selected in males. We measured male ability to compete for fertilizations, at young and late ages, across 25 cytoplasms expressed in three different nuclear genetic backgrounds, within a population of Drosophila melanogaster. We found no cytoplasmic (thus no mtDNA) genetic variation for either male offence or offensive sperm competitiveness. This contrasts with previous findings demonstrating cytoplasmic genetic variation for female fitness and female ageing across these same lines. Taken together, this suggests that mitochondrial genes do not contribute to variation in sperm competition at the within-population level.     

黑腹果蝇的性别控制

性别的形成包括两个过程,即性别决定和性别分化。果蝇的性别控制研究包括性别决定、性别分化、性别鉴定、性别诱导和性别控制5个方面。性别决定是在两种不同发育途径之间的选择,它提供了一个研究基因调控的模式系统。果蝇的性别决定问题已经研究得相当详细［1］。性别分化是使胚胎向着雌性或雄性发育的过程,决定了性别表型。果蝇的性别分化也取得了不少研究成果。近年来,许多重要的性别调控基因已被克隆和鉴定。随着果蝇基因组全序列测定的完成,果蝇的性别控制研究将会更为深入而完善。本文对与黑腹果蝇性别决定和性别分化相关的一些问题进行综述。     

Increase in cold-shock tolerance by selection of cold resistant lines in Drosophila melanogaster

Abstract.

• 1 In Drosophila melanogaster, the cold-shock tolerance of adult flies at -7°C increased 22% after a prior 2h exposure to 4°C as measured by LD₅₀, the dose (degree minutes of exposure to subzero temperature) which resulted in 50% mortality.
• 2 Cold-shock tolerance was further significantly increased by selecting cold resistant lines by exposure of adults (1) to 4°C for 2 h (short-term chilling), or (2) to -7°C for 80–120 min (cold shock), or (3) to short-term chilling followed by cold-shock.
• 3 After ten generations of selection, the greatest increase in cold-shock tolerance was found in flies selected using the combined exposure of short-term chilling and cold shock. LD₅₀s increased 33% in comparison with the unselected control strain when no chilling pre-treatment was given prior to cold shock at -7°C.
• 4 The rapid cold-hardening response increased 82% in the line selected by the short-term chilling and cold-shock regime.
• 5 The enhanced cold-shock tolerance was relatively stable since no decrease was observed after four generations without selection.
• 6 This report shows the role of short-term adaptation as well as selection in the capacity to survive low temperatures in non-diapausing stages of insects.

     

Genome scans of variation and adaptive change: extended analysis of a candidate locus close to the phantom gene region in Drosophila melanogaster

Nucleotide variation in populations originating from the recent range expansion of a species should reflect their adaptation to new habitats as well as their demographic history. A survey of nucleotide variation at 109 noncoding X-chromosome fragments in a European population of Drosophila melanogaster allowed identifying some candidates to have been recently affected by positive selection. Adaptive changes leave a spatial differential footprint that can be used to discriminate among candidates by extending their study to neighboring regions. Here, we surveyed variation at an approximately 190-kb region spanning a locus exhibiting a significantly skewed frequency spectrum. A stretch of approximately 12 kb with reduced variation was detected within a continuously sequenced region that included the focal fragment. Moreover, the regions flanking this stretch exhibited an excess of high-frequency derived variants. Application of maximum likelihood ratio and goodness-of-fit tests suggested that the pattern of variation detected at the studied region (at cytological bands 17C-17D) might have been shaped by a recent selective change, most probably at or around the phantom gene that encodes CYP306A1, a cytochrome P450 enzyme in the ecdysteroidogenic pathway.     

Geographical variation in AdhF and alcoholic resource utilization in Indian populations of Drosophila melanogaster

Indian geographical populations of Drosophila melanogaster, collected at latitude 10–32.3 ^oN, longitude 76.1–80.1 ^oE and altitude 16–2050 m, were analysed for changes in Adh ¹ frequency and utilization potential of diverse alcoholic resources. Until now, there have been limited data on climatic association of correlated changes on these aspects in continental populations of D. melanogaster. Indian populations demonstrate an increase in Adh ^F frequency by 0.04 per degree latitude and significantly higher utilization of ethanol (9.0–15.2%), acetic acid (8.1–12.5%), n-propanol (2.55-4.25%), 2-propanol (1.5-3.5%), n-butanol (2.15 3.5%) and 2-butanol (0.68-1.2%). Data also revealed significant correlation with latitude as well as altitude. Regression analysis of climatic data from collection sites confirmed the observed clinal variation of Adh ^F as well as alcoholic utilization in D. melanogaster. On the Indian subcontinent, variation in Adh ^F frequency and alcoholic resource utilization along increasing latitude as well as altitude are due to climatic selection factors such as temperature and rainfall.