果蝇Drosophila nasuta亚群系统发育问题的探讨

果蝇Ｄｒｏｓｏｐｈｉｌａｎａｓｕｔａ亚群由在１４个处于不同物种分化阶段的种,亚种和分类元组成,这个亚群的物种有许多进化上的独特之处,使得它在物种分化研究方面倍受关注,然而,在形态学,生殖隔离,染色体和同工酶多态,线粒体ＤＮＡＲＦＬＰ,求偶歌特征惟及线粒体和核基因序列分析等方面的研究都未能清楚地阐明这一亚群的系统进化关系,本文综合分析了关于这一亚群的进化遗传学的研究结果,并提出了有待进一步的一些问题     

Evolutionary relationships to parasitism by seven species of the Drosophila melanogaster subgroup

Parasitic wasps are an important component of the niche of Drosophila species. The susceptibility to the Cynipid Leptopilina boulardi was estimated in the seven sibling species of Drosophila belonging to the melanogaster subgroup. Three categories of Hies can be distinguished, according to the level of cellular immune reaction and success of parasitism. Drosophila melanogaster and D. mauritiana belong to the category 1, specified by no encapsulative reaction and a high rate of successful parasitism. Category 2, characterized by a moderate encapsulation rate and a high mortality include D. simulans.5, D. erecta and D. orena . Category 3, with D. yakuba and D. tcissien , is specified by a very low rate or absence of successful parasitism due to a highly efficient immune cellular reaction. This classification parallels the phylogenic relationship based upon polytene chromosome banding sequences. Such specific ditferences in susceptibility to parasites may plan an important role in the competition between these species in Africa.     

Evolutionary relationships to parasitism by seven species of the Drosophila melanogaster subgroup

Parasitic wasps are an important component of the niche of Drosophila species. The susceptibility to the Cynipid Leptopilina boulardi was estimated in the seven sibling species of Drosophila belonging to the melanogaster subgroup. Three categories of Hies can be distinguished, according to the level of cellular immune reaction and success of parasitism. Drosophila melanogaster and D. mauritiana belong to the category 1, specified by no encapsulative reaction and a high rate of successful parasitism. Category 2, characterized by a moderate encapsulation rate and a high mortality include D. simulans.5, D. erecta and D. orena. Category 3, with D. yakuba and D. tcissien, is specified by a very low rate or absence of successful parasitism due to a highly efficient immune cellular reaction. This classification parallels the phylogenic relationship based upon polytene chromosome banding sequences. Such specific ditferences in susceptibility to parasites may plan an important role in the competition between these species in Africa.     

Evolution of abdominal pigmentation differences across species in the Drosophila dunni subgroup

The Drosophila dunni subgroup displays a nearly perfect latitudinal cline in abdominal pigmentation that likely resulted from selective forces acting in the habitat of each species during speciation. Here we characterize the nature of this clinal variation by developing a quantitative measure to assess variation in abdominal pigmentation within and between the D. dunni subgroup species. Using discriminant analysis, we confirm the existence of a cline and find that our quantitative measure of pigmentation distinguishes each of the species with singular efficacy. We then combine our quantitative phenotypic analysis of pigmentation with the phylogeny of the D. dunni subgroup species and map the species relationships into the three-dimensional morphological space defined by our pigmentation measures. In this manner, we can visualize how the species have traversed the morphological pigmentation space during the course of speciation. Our analysis reveals that natural selection has caused overall intensity of pigmentation among the northernmost species of the cline to converge. Along with this convergence in phenotype has been a relaxation in expression of sexual dimorphism in these species, indicating a possible shift in the relative intensity of natural and sexual selection. Our analysis indicates an accelerated rate of change in pigmentation for the darkest species in addition to this species evolving a novel abdominal pigmentation trait.     

Egg size,embryonic development time and ovoviviparity in Drosophila species

Lengths, widths and volumes of eggs from 11 species of Drosophila whose genomes have been fully sequenced exhibit significant variation that is not explained by their phylogenetic relationships. Furthermore, egg size differences are unrelated to embryonic development time in these species. In addition, two of the species, Drosophila sechellia and, to a lesser degree, D. yakuba, both ecological specialists, exhibit ovoviviparity, suggesting that female control over oviposition in these species differs from what is observed in D. melanogaster. The interspecific differences in these reproductive characters, coupled with the availability of whole genome sequences for each, provide an unprecedented opportunity to examine their evolution.     

亚高寒草甸不同生境植物群落物种多度分布格局的拟合

物种多度分布是群落生态学研究的核心内容。通过对青藏高原东部亚高寒草甸3种不同生境草本植物群落的抽样调查,结合16个物种多度分布模型的两种曲线拟合优度检验得出如下结果：多种不同模型可以拟合同一生境的物种多度分布。相比于其他可拟合模型,几何级数模型在3种生境中两种拟合优度检验方法下的平均拟合效果是最好的,拟合优度值均在最优拟合优度值10左右波动。次优模型鉴于不同生境不同的检验方法表现不一。除了几何级数模型外,Sugihara分数模型在最小二乘法的拟合方法下,也可以拟合3种生境的物种多度分布。研究结果表明,仅用拟合优度检验区分产生不同物种分布格局的模型和机制是不可靠的,需要做进一步的检验性实验研究。     

Genetic and developmental analysis of abdominal pigmentation differences across species in the Drosophila dunni subgroup

Abdominal pigmentation pattern varies dramatically among the species of the Drosophila dunni subgroup across the islands of the Caribbean. Previously, we developed a quantitative measure of abdominal pigmentation to assess phenotypic variation within and between species of this group. In this paper, we use this quantitative measure in an interspecific genetic analysis to decipher the underlying genetic basis of pigmentation differences between one of the lightest and the darkest species in the group. Our analysis shows that pigmentation expression in different areas of the abdomen is under separate genetic control. For these different abdominal regions, we detected a wide range of genetic effects, including X-linked, autosomal additive, near single-gene dominant, and sex-specific effects. Combining these genetic results with our earlier phenotypic and phylogenetic analyses, we present a simple conceptual model to explain how change in the control of expression of pigmentation has evolved throughout the D. dunni subgroup.     

Drosophila subpulchrella, a new species of the Drosophila suzukii species subgroup from Japan and China (Diptera: Drosophilidae)

Drosophila (Sophophora) subpulchrella Takamori and Watabe, sp. nov., of the D. suzukii subgroup in the D. melanogaster species group, is described from Japan and southern China, and compared with its sibling species, D. pulchrella Tan et al. distributed in the Yun‐Gui Highland, south‐western China. The results of cross‐experiments show a complete pre‐mating isolation between D. subpulchrella and D. pulchrella.     

Identification of the sibling species of the Drosophila willistoni subgroup through the electrophoretical mobility of acid phosphatase-1

The Drosophila willistoni group consists of 23 species of which six are sibling species and belong to the D. willistoni subgroup: D. willistoni, Drosophila equinoxialis, Drosophila tropicalis, Drosophila insularis, Drosophila pavlovskiana and Drosophila paulistorum. These sibling species are abundant in the Neotropical region and can hardly be differentiated by the usual taxonomic traits. Four of them (D. willistoni, D. equinoxialis, D. tropicalis and D. paulistorum) cover extensive geographic distribution areas overlapping in places while two of them are endemic (D. insularis and D. pavlovskiana). In this study, we presented a method for the identification of five sibling species of the D. willistoni subgroup based on the allozyme variation of acid phosphatase‐1 (Acph‐1) in acrylamide gel electrophoresis. Our work showed that Acph‐1 allozyme differences can be used for species‐diagnostic characterization. This method was shown to be a more efficient tool for species identification than others because it is both quicker and produces reliable results.     

Rapid evolution and gene-specific patterns of selection for three genes of spermatogenesis in Drosophila

Hybrid males resulting from crosses between closely related species of Drosophila are sterile. The F1 hybrid sterility phenotype is mainly due to defects occurring during late stages of development that relate to sperm individualization, and so genes controlling sperm development may have been subjected to selective diversification between species. It is also possible that genes of spermatogenesis experience selective constraints given their role in a developmental pathway. We analyzed the molecular evolution of three genes playing a role during the sperm developmental pathway in Drosophila at an early (bam), a mid (aly), and a late (dj) stage. The complete coding region of these genes was sequenced in different strains of Drosophila melanogaster and Drosophila simulans. All three genes showed rapid divergence between species, with larger numbers of nonsynonymous to synonymous differences between species than polymorphisms. Although this could be interpreted as evidence for positive selection at all three genes, formal tests of selection do not support such a conclusion. Departures from neutrality were detected only for dj and bam but not aly. The role played by selection is unique and determined by gene-specific characteristics rather than site of expression. In dj, the departure was due to a high proportion of neutral synonymous polymorphisms in D. simulans, and there was evidence of purifying selection maintaining a high lysine amino acid protein content that is characteristic of other DNA-binding proteins. The earliest spermatogenesis gene surveyed, which plays a role in both male and female gametogenesis, was bam, and its significant departure from neutrality was due to an excess of nonsynonymous substitutions between species. Bam is degraded at the end of mitosis, and rapid evolutionary changes among species might be a characteristic shared with other degradable transient proteins. However, the large number of nonsynonymous changes between D. melanogaster and D. simulans and a phylogenetic comparative analysis among species confirms evidence of positive selection driving the evolution of Bam and suggests an yet unknown germ cell line developmental adaptive change between these two species.     

Contrasting patterns of geographic variation in the cosmopolitan sibling species Drosophila melanogaster and Drosophila simulans

An electrophoretic study was carried out to compare the geographic pattern of genetic variation in Drosophila simulans with that of its sibling species, Drosophila melanogaster. An identical set of 32 gene-protein loci was studied in four geographically distant populations of D. simulans and two populations of D. melanogaster, all originating from Europe and Africa. The comparison yielded the following results: (1) tropical populations of D. simulans were, in terms of the number of unique alleles, average heterozygosity per locus, and percentage of loci polymorphic, more variable than conspecific-temperate populations; (2) some loci in both species showed interpopulation differences in allele frequencies that suggest latitudinal clines; and (3) temperate-tropical genetic differentiation between populations was much less in D. simulans than in D. melanogaster. Similar differences between these two species have previously been shown for chromosomal, quantitative, physiological, and middle-repetitive DNA variation. Estimates of N _m (number of migrants per generation) from the spatial distribution of rare alleles suggest that both species have similar levels of interpopulation gene flow. These observations lead us to propose two competing hypotheses: the low level of geographic differentiation in D. simulans is due to its evolutionarily recent worldwide colonization and, alternatively, D. simulans has a narrower niche than D. melanogaster. Geographic variation data on different genetic elements (e.g., mitochondrial DNA, two-dimensional proteins, etc.) are required before these hypotheses can be adequately tested.We thank the Natural Science and Engineering Research Council of Canada for financial support (Grant A0235 to R.S.S.).     

Seasonal patterns of abundance,distributions, and phenology in relation to growth strategies of three Sargassum species

Seasonal patterns of abundance of Sargassum johnstonii Setchell & Gardner, S. herporhizum Setchell & Gardner, and S. sinicola Setchell & Gardner var. camouii (Dawson) Norris & Yensen were observed in the northern Gulf of California where mean monthly sea temperatures range annually from < 14 °C to nearly 30 °C. The three species displayed peaks in size, canopy cover, and fertility in the spring, in between periods of seasonal temperature extremes. Larger plants were the first to develop reproductive structures, suggesting that a threshold in size must be reached before plants become fertile. Fertile receptacles were shed in summer. S. sinicola var. camouii retained a greater portion of its primary stipes during the summer dieback than the other two species and showed a second peak in fertility in fall. Whereas tropical Sargassum are most abundant in winter and temperate-zone Sargassum are most abundant in summer months, the Gulf of California species achieve maximum size and fertility in between seasons of extreme temperatures. A long-term decline in abundance of Sargassum was observed at the study site between 1977 and 1981, possibly due to the detrimental effects on Sargassum of anomalously warm sea temperatures in the Gulf of California in 1978 or to the subsequent effects of warm temperature on food webs in the region.     

Molecular evolution of the histone 3 multigene family in the Drosophila melanogaster species subgroup

Molecular evolution of the histone multigene family was studied by cloning and sequencing regions of the histone 3 gene in the Drosophila melanogaster species subgroup. Analysis of the nucleotide substitution pattern showed that in the coding region synonymous changes occurred more frequently to A or T in contrast to the GC-rich base composition, while in the 3' region the nucleotide substitutions were most likely in equilibrium. These results suggested that the base composition at the third codon position of the H3 gene, i.e., codon usage, has been changing to A or T in the Drosophila melanogaster species subgroup.     

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.     

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

In interspecific matings between the species Drosophila virilis and Drosophila texana, female sterility can be observed in F₂ backcross females and in F₂ hybrid females. The results presented in this report show that the female sterility, whenever it exists, is due to prevention of vitellogenin synthesis in the fat body, but other abnormalities such as defects with the hybrid ovaries are not excluded. The observation that sterility appears among females from backcrosses suggests that incompatibilities between interspecific genes may cause female sterility even in the presence of a complete habloid genome from one or the other species. Yet, the parallel observation that female sterility appears only in hybrid females with recombinant chromosomes indicates that sterility results when conspecific combinations of genes on the same chromosome are broken by interspecific recombination. © 1996 Wiley-Liss, Inc.     

Temperature and clinal variation in larval growth efficiency in Drosophila melanogaster

Geographic clines in ectotherm species including Drosophila melanogaster have been found throughout the world, with genetically larger body size and shorter development time occurring at high latitudes. Temperature is thought to play a major role in the evolution of this clinal variation. Laboratory thermal selection has effects similar to those seen in geographical clines. Evolution at low temperatures results in more rapid development to larger adult flies. This study investigated the effects of geographical origin and experimental temperature on larval growth efficiency in D. melanogaster. Larvae from populations that had evolved at high latitudes were found to use limited food more efficiently, so that the overall adult body size achieved was larger. Larvae reared at a lower experimental temperature (18 °C) used food more efficiently than those reared at a higher temperature (25 °C). The increases in growth efficiency found in populations from high latitudes could explain their increased body size and more rapid development.