Different mechanisms underlie phenotypic plasticity and interspecific variation for a reproductive character in drosophilids (Insecta: Diptera)

The insect ovary is a modular structure, the functional unit of which is the ovariole. Ovariole number is positively correlated with potential reproductive output. Among drosophilids (Insecta: Diptera), ovariole number shows both phenotypic plasticity and substantial interspecific and interpopulational variation. Here we examine the mechanistic connection between phenotypic plasticity and genetically fixed variation in ovariole number within the melanogaster species group. When a laboratory population of Drosophila melanogaster was reared under reduced food conditions, differences in ovariole number were entirely due to alterations in cell differentiation during the wandering stage at the very end of larval development. Cell growth and cell death were not affected. When these same flies were reared under a variety of temperatures, ovariole number differences arose during the latter half of the third (final) larval instar. Cell differentiation was affected, although cell number was not, and ovariole number differences were established before metamorphosis. In contrast, genetically fixed, interspecific and interpopulational variability in ovariole number was caused by alterations in the dynamics of cell differentiation and by cell number differences. Furthermore, the stages affected were different in different species and populations in the melanogaster species group, ranging from the first (D. sechellia) through the middle of the third (D. simulans and D. mauritiana) larval stage. Therefore, the mechanistic bases for plasticity-based variability are largely distinct from the mechanistic bases for interspecific and interpopulational variability. Our results suggest that phenotypic plasticity indicates evolutionary flexibility in underlying ontogenetic processes.     

THE GENETICS OF AN ISOLATING MECHANISM BETWEEN TWO SIBLING SPECIES OF DROSOPHILA

Matings between Drosophila simulans females and males of the sibling species D. mauritiana are of abnormally short duration. These rapid matings interrupt the transfer of sperm, leading to substantial reproductive isolation in interspecific as compared to intraspecific copulations. Genetic analysis of this behavior shows that it is influenced much more by the male than the female genotype, with genes from D. simulans being dominant. In males, shortened copulation is caused by interspecific divergence at a minimum of three loci, with one gene on each of the major chromosomes. This is an underestimate of the true number of loci affecting the trait, which could be much larger. The two autosomes have the largest effect, whereas that of the X chromosome is much smaller. The genetic architecture of copulation duration and the larger effect of male than female genotype suggest that females can detect and discriminate against differences in male genitalia.     

Population genetic study of allozyme variation in natural populations of Drosophila antonietae (Insecta, Diptera)

Drosophila antonietae is an endemic South American cactophilic species found in relictual xerophytic vegetation, mostly associated with Cereus hildmaniannus cactus. Low differentiation among populations of this species has been detected using several markers. In this work, we performed an allozyme genetic variability analysis of 11 natural populations of D. antonietae and included a discussion about the possible influences of several evolutionary processes that might be acting to maintain the pattern observed. The genetic variability of 14 isoenzyme loci was analysed and showed a high genetic diversity (average observed heterozygosity = 0.319) and a moderate genetic differentiation among populations ( F statistics = 0.0723). A correlation between genetic and geographical and ecological distances was detected among pairs of populations and the regional equilibrium analysis was thus applied. This analysis resulted in Nm (number of migrants) of approximately 3.21, indicating that moderate levels of both gene flow and genetic drift occur in this species, with gene flow overlapping genetic drift. However, considering ecological features of drosophilids, we propose a hypothesis to explain the moderate differentiation encountered as a result of three different processes, or a combination of them: (1) gene flow; (2) a short period of differentiation, i.e. maintenance of ancestral polymorphism; and (3) action of natural selection. Moreover, if gene flow is present, the high genetic diversity compared with other cactophilic and non-cactophilic species could be due to differential selection in different populations followed by gene exchange among them. These factors are discussed in the light of D. antonietae 's historical and evolutionary association with the host cactus.     

Ecology and population genetics of Sonoran Desert Drosophila

Three species of cactophilic Drosophila endemic to the Sonoran Desert of North America, D. nigrospiracula, D. pachea and D. mettleri, experience marked differences in spatial resource availability, and the first two of these display significant differences in dispersal behaviour. We employed starch gel and cellulose acetate electrophoresis for eight allozyme loci to test for a relationship between these variables and genetic differentiation among geographical populations of each species. No evidence was found for population structure in any of the three species, populations of which were separated by geographical distances of up to 475 km. Allele frequencies for two loci, Mdh-1 and Est-2, in D. nigrospiracula and D. pachea were very similar to those obtained approximately 30 years ago by other workers, indicating that the polymorphisms are remarkably stable under the stressful and variable conditions of the desert environment. High longevity, dispersal and multiple female remating are likely to contribute to the apparent high level of gene flow in all three species.     

Can competition be superior to parasitism for biological control? The case of spotted wing Drosophila (Drosophila suzukii), Drosophila melanogaster and Pachycrepoideus vindemmiae

Drosophila suzukii and Drosophila melanogaster coexist with different but overlapping resource use in the field. When forced to completely or partially share resources in the laboratory, D. melanogaster outcompetes D. suzukii. Adult D. suzukii and D. melanogaster females were allowed to compete for access to a common oviposition resource in pairwise and population scale experiments. We tracked the offspring emergence to explore the factors across life stages that might affect the success of D. suzukii in the laboratory compared to a closed field simulation cage experiment with a generalist Drosophila parasitoid, Pachycrepoideous vindemmiae. When in competition as adults, D. melanogaster produced more offspring that survived to pupation than D. suzukii. In addition, D. melanogaster produced more offspring when in competition with a conspecific than when in competition with D. suzukii. Competitor identity did not affect the number of D. melanogaster offspring in pairwise and cage experiments. However, in the presence of D. melanogaster, the number of D. suzukii offspring in both pairwise and cage experiments was dramatically reduced than in cages without this competitor. In the presence of both D. melanogaster and P. vindemmiae, there were marginally more D. suzukii than when only D. melanogaster was present. These results suggest that competition was an important factor limiting D. suzukii numbers. Limiting D. suzukii numbers through interspecies competition may eventually be an exploitable method of biocontrol in the field.     

Simple Synthesis of the Major Sex Pheromone Components of Drosophila ananassae and D. pallidosa

The major sex pheromone components of Drosophila ananassae and D. pallidosa, (Z,Z)-5,25-hentriacontadiene and (Z,Z)-5,27-tritriacontadiene, respectively, were synthesized by using the Wittig olefination and sulfone coupling reactions as the C–C bond-forming steps.     

Interspecific transfer of P elements by crosses between Drosophila simulans and Drosophila mauritiana

Interspecific crosses were carried out between P element-transformed strains of D. simulans and a strain of D. mauritiana, a species devoid of this transposable element family. Four lines were established from hybrid females backcrossed with D. mauritiana males for four generations, and then maintained by intra-line mass mating. In situ hybridization of polytene chromosomes and southern blots showed that full-length and deleted P elements were present in all of the lines after 15 generations. We conclude that at least some of the P elements observed in two lines result from their transposition into D. mauritiana genome. Gonadal sterility, induced at 29°C in D. melanogaster by P elements also occurred with these two latter lines.     

Inferring the evolutionary history of Drosophila americana and Drosophila novamexicana using a multilocus approach and the influence of chromosomal rearrangements in single gene analyses

The evolutionary history of closely related organisms can prove sometimes difficult to infer. Hybridization and incomplete lineage sorting are the main concerns; however, genome rearrangements can also influence the outcome of analyses based on nuclear sequences. In the present study, DNA sequences from 12 nuclear genes, for which the approximate chromosomal locations are known, have been used to estimate the evolutionary history of two forms of Drosophila americana ( Drosophila   americana americana and Drosophila americana texana ) and Drosophila novamexicana ( virilis group of species). The phylogenetic analysis of the combined data set resulted in a phylogeny showing reciprocal monophyly for D. novamexicana and D. americana . Single gene analyses, however, resulted in incongruent phylogenies influenced by chromosomal rearrangements. Genetic differentiation estimates indicated a significant differentiation between the two species for all genes. Within D. americana , however, there is no evidence for differentiation between the chromosomal forms except at genes located near the X/4 fusion and Xc inversion breakpoint. Thus, the specific status of D. americana and D. novamexicana is confirmed, but there is no overall evidence for genetic differentiation between D. a. americana and D. a. texana , not supporting a subspecific status. Based on levels of allele and nucleotide diversity found in the strains used, it is proposed that D. americana has had a stable, large population during the recent past while D. novamexicana has speciated from a peripheral southwestern population having had an ancestral small effective population size. The influence of chromosomal rearrangements in single gene analyses is also examined.     

Effects of mycotoxin pretreatment on aflatoxin B1 post-treatment toxicity in Drosophila melanogaster (Diptera)

Two wild-type laboratory strains of Drosophila melanogaster were used in this study: strain Flordia-9, which is sensitive to aflatoxin B₁ (AFB₁)-induced toxicity, and strain Lausanne-S, which is resistant. Eggs of these strains were deposited on medium containing either low or high doses of dietary AFG₁, AFB₂, or sterigmatocystin (ST) and allowed to develop into second instar larvae. After this pretreatment, the larvae were transferred onto medium containing either high or low doses of dietary AFB₁ (post-treatment) and allowed to complete development and eclose as adults. Viability and development data were analyzed to determine the effects of the various pretreatments on the level of AFB₁-induced toxicity in the post-treatments. In no case did any of the pretreatments reduce the toxic effects of AFB₁ post-treatment responses. However, for strain Florida-9, all high-dose pretreatments resulted in enhanced post-treatment toxicity, and all low-dose pretreatments also enhanced toxicity of high-dose post-treatments. For strain Lausanne-S, high-dose AFB₂ pretreatment significantly enhanced toxicity of both high- and low-dose post-treatments. These results indicate that, in strain Florida-9, pretreatment with relatively less toxic mycotoxins (ST and AFB₂) has an enhancing effect on AFB₁-induced toxicity, whereas in strain Lausanne-S, a similar but smaller enhancing effect is seen only with AFB₂ pretratment.     

DMAP-85: A τ-Like Protein from Drosophila melanogaster Larvae

Abstract: Microtubule-associated proteins (MAPs) play major regulatory roles in the organization and integrity of the cytoskeletal network. Our main interest in this study was the identification and the analysis of structural and functional aspects of Drosophila melanogaster MAPs. A novel MAP with a relative molecular mass of 85 kDa from Drosophila larvae was found associated with taxol-polymerized microtubules. In addition, this protein bound to mammalian tubulin in an overlay assay and coassembled with purified bovine brain tubulin in microtubule sedimentation experiments. The estimated stoichiometry of 85-kDa protein versus tubulin in the polymers was 1:5.3 ± 0.2 mol/mol. It was shown that the 85-kDa protein bound specifically to an affinity column of Sepharose-βII-(422–434) tubulin peptide, which contains the sequence of the MAP binding domain on βII-tubulin. Affinity-purified 85-kDa protein enhanced microtubule assembly in a concentration-dependent manner. This effect was significantly decreased by the presence of the βII-(422–434) peptide in the assembly assays, thus confirming the specificity of the 85-kDa protein interaction with the C-terminal domain on tubulin. Furthermore, this protein also exhibited a strong affinity for calmodulin, based on affinity chromatographic assays. Monoclonal and polyclonal anti-τ antibodies, including sequence-specific probes that recognize repeated microtubule-binding motifs on τ, MAP-2, and MAP-4 and specific N-terminal sequences of τ, cross-reacted with the 85-kDa protein from Drosophila larvae. These results suggest that τ and Drosophila 85-kDa protein share common functional and structural epitopes. We have named this protein as DMAP-85 for Drosophila MAP. The finding on a Drosophila protein with functional homology and structural similarities to mammalian τ opens new perspectives to understand the cellular roles of MAPs.     

用RAPD标记探讨金色果蝇复合种内的遗传分化

以随机扩增多态性DNA（RAPD）技术分析了金以果蝇复合种的5个姊妹种（Drosophile auraria、D．biauraria、D.triauraria、D．quadraria和D．subauraria）共12个地理种群的遗传变异。在40种10碱基随机引物中有30种引物对每个种群都可获得令人满意的扩增结果。在161个RAPD标记中有129个呈多态性。以遗传距离为尺度用UPGMA法构建了该复合种的聚类关系图。聚类分析结果结果表明：D.subauraria处于聚类关系图的基部,为该复合种中最早分化的种类;其后才是D.biauraria的分化,而D.auraria和D.quadraria的分化相对较晚。此结果不支持以往认为D.quadraria为金色果蝇复合种祖先种的观点。RAPD分子标记为金色果蝇复合种的系统演化的研究提供了新的、更有价值的信息。     

Correlations between measures of heat resistance and acclimation in two species of Drosophila and their Hybrids

Associations between traits may differ at the interspecific and intraspecific levels, making it difficult to predict long term evolutionary constraints. In this study we used replicate hybrid lines generated from crosses between Drosophila serrata and D. birchii to investigate correlations between measures of heat resistance and acclimation responses. Within each species, knockdown heat resistance was uncorrelated with heat resistance as measured by mortality. In contrast, D. serrata was more resistant than D. birchii for both measures of heat resistance. Thus, inter- and intraspecific correlations between measures of heat resistance differ. In the hybrids, there was no evidence for a correlation between knockdown time and heat induced mortality. Hybrid data did suggest a trade-off between acclimation for knockdown heat resistance and heat resistance as measured by mortality. We argue that hybrids between species are a potentially useful tool for studying traits such as acclimation responses that show litde genetic variation within species.     

Ovarian defects in hybrids of the species pair Drosophila virilis and Drosophila texana

In interspecific matings between Drosophila virilis and Drosophila texana female sterility is observed in F₂ hybrid females. A previous study has shown that no vitellogenin synthesis occurs in the fat body of sterile hybrid females. The results presented in this paper show that hybrid ovaries of sterile females transplanted into the abdomens of females of the parental species are not able to develop upon maturity. With few exceptions, the hybrid ovaries remained alive in the host environment, but their oocytes failed to develop to vitellogenic stages. Thus, in hybrid females between Drosophila virilis and Drosophila texana sterility is the result of defects in both the two main developmental processes of egg maturation, the synthesis of vitellogenins in the fat body and the uptake of vitellogenins by the ovary. Dev Genet 20:47–52, 1997. © 1997 Wiley-Liss, Inc.     

中国黑腹果蝇种组40种果蝇的核型多样性研究

通过传统的敲片、Giemsa染色的方法制片对中国黑腹果蝇种组(Drosophilamelanogasterspeciesgroup)8个种亚组40种果蝇的染色体进行了分析,共发现18种核型,即A、A′′、C、C′、C′′、C′′′、C′′′′、D、D′、D′′、E、E′、E′′、F、F′、G、H和I,其中A、A′′、C′′′、C′′′′、D′′和F′为新发现的核型。8个种亚组的基本核型分别是:嗜凤梨果蝇种亚组(D.ananassaesubgroup)的核型为F、F′、G和H型;牵牛花果蝇种亚组(D.eleganssubgroup)的核型为A和A′′型;细针果蝇种亚组(D.eugracilissubgroup)的核型为C型;嗜榕果蝇种亚组(D.ficusphilasubgroup)的核型为C′型;黑腹果蝇种亚组(D.melanogastersubgroup)的核型为C和C′型;山果蝇种亚组(D.montiumsubgroup)的核型为C、C′、C′′、D、D′、D′′、E、E′、E′′和I型;铃木氏果蝇种亚组(D.suzukiisubgroup)的核型为C′′′和C′′′′型;高桥氏果蝇种亚组(D.takahashiisubgroup)的核型为C、C′′′和C′′′′型。透明翅果蝇(D.lucipennis)雌性核型2n=8,雄性核型2n=7,雄性Ⅳ号染色体为染色体单体。此外还发现,吉川氏果蝇(D.kikkawai)、林氏果蝇(D.lini)、奥尼氏果蝇(D.ogumai)、拟嗜凤梨果蝇(D.pseudoananassae)和叔白颜果蝇(D.triauraria)5种果蝇有B染色体。本文确定了D.sp.likeelegans、D.sp.likenyinyii、D.sp.liketrapezifrons1、D.sp.liketakahashii、D.sp.liketrapezifrons2和D.sp.likeauraria等6个未描述种的核型和1个新记录种吉里果蝇(D.giriensis)的核型。本研究证明了在黑腹果蝇种组内、亚组内、种内和单雌系内的核型多样性,为果蝇遗传和进化提供了进一步的细胞学证据。     

Spontaneous emergence of a new Wolbachia phenotype

Wolbachia are among the most widespread symbionts on the earth. They spread within populations by various means of manipulating host reproduction, including cytoplasmic incompatibility (CI), male-killing (MK), parthenogenesis, and feminization. Phylogenetic analyses indicate that Wolbachia have the potential to undergo rapid evolutionary change in phenotype, for example, from CI to MK, although such analyses do not reveal the rate at which such transitions occur, nor the nature of the intermediate phenotypes. Here I show that a transition from CI to MK can occur almost instantaneously on an evolutionary time scale. A Wolbachia strain that causes CI in its natural host, Drosophila recens, was introgressed to its sister species D. subquinaria via the natural processes of hybridization and backcrossing. In some strains of D. subquinaria, infection with this Wolbachia strain caused essentially complete MK, resulting in all-female broods, whereas in other strains, there was no effect on offspring sex ratio. Crosses within and between D. subquinaria and D. recens revealed that resistance to MK is dominant, autosomal, multigenic, and dependent on zygotic, not maternal, genotype. MK in D. subquinaria is unusual in that the male offspring of infected females die during the larval stage, not as embryos. These findings suggest that MK and CI may share a similar underlying molecular basis.     

Resistance to temperature extremes between and within life cycle stages in Drosophila serrata, D. birchii and their hybrids: intraspecific and interspecific comparisons

Intraspecific Drosophila studies suggest that resistance to heat and cold stresses are largely independent and that correlations across life cycle stages are low whereas comparisons of Drosophila species indicate correlations between heat and cold resistance as well as between resistance levels in different life cycle stages. These inconsistent results may reflect differences in associations among traits at the interspecific and intraspecific levels or interspecific correlations arising because of correlated selection pressures. These alternatives were tested using Drosophila serrata, D. birchii and hybrids derived from these species. Variation among hybrid lines and families was used to test associations at the interspecific level while intraspecific variation was examined using isofemale lines ol'D. serrata. There was a significant association between adult heat knockdown time at 38^oC and adult cold resistance in one set of hybrid lines. An association between female knockdown resistance to heat and larval heat resistance was also evident in one set of hybrids. Resistance to heat and cold at the larval stage were not correlated at either the intraspecific or interspecific levels. At the intraspecific level, larval heat resistance and two measures of adult heat resistance were uncorrected. Moreover, adult and larval cold resistance measures were not correlated at either the intraspecific or interspecific levels. These results suggest that there arc no associations between resistance to heat and cold extremes and that extreme temperature resistance is largely independent across life cycle stages at both the intraspecific and interspecific levels. Species associations may therefore arise from correlated selection pressures rather than trait correlations.     

Variations in the esterase expression pattern with respect to different light regimes in Drosophila agumbensis and Drosophila nagarholensis

Circadian clock enables organism’s to adapt under fluctuating environmental conditions by coupling of behavioral, physiological and molecular processes in a wide variety of organisms including bacteria, fungi, plants, birds and mammals. The endogenous circadian system functions to organize behavior and physiology to adapt to and anticipate environment changes in light and temperature. The present study is an attempt to understand enzyme profiles (alpha- and beta-esterases) of Drosophila agumbensis and Drosophila nagarholensis under light/dark (LD), constant dark (DD) constant light (LL), conditions over twenty generations. A polyacrylamide gel electrophoresis (7.5% – Native gel) was used to study the esterase expression patterns in two species of the montium subgroup of Drosophila. Alpha- and beta-esterase expression was significantly decreased in LL when compared to LD and DD at both the generations and species. In all the light regimes, females were found to have significantly higher level of α- and β-esterase expression than males. Flies were maintained under different light regimes showed difference in their expression patterns with respect to alpha- and beta-esterases. The present study showed that constant light conditions affect the expression of esterases in D. agumbensis and D. nagarholensis.     

中国特有的弯头果蝇种亚组及二新种记述(双翅目，果蝇科)

本文记述弯头果蝇种亚组的二新种,施氏果蝇 Drosophila (Drosophila) shi sp. nov.,短乳突果蝇Drosophila (Drosophila) brevipapilla sp.nov.,并对中国特有的弯头果蝇种亚组中11 个种的分布进行了分析。