双翅目昆虫（黑腹果蝇和冈比亚按蚊）内含子丢失的比较分析

内含子插入和丢失的进化动力及机制尚存在许多疑问。通过对真核生物的105个同源基因的蛋白质高度保守区域内含子-外显子结构的研究,对人Homo sapiens、小鼠Mus musculus、大鼠Rattus norvegicus、黑腹果蝇Drosophila melanogaster、冈比亚按蚊Anopheles gambiae和秀丽隐杆线虫Caenorhabditis elegans的3 574个内含子、1 001个的内含子保守位点进行分析,推断出不同系统中内含子的变化途径。发现在进化早期,脊椎动物、双翅目昆虫和线虫的共同祖先中含有大量内含子,在进化过程中,双翅目昆虫和线虫发生了大量的内含子丢失,甚至在双翅目昆虫中内含子丢失较线虫更严重。线虫获得的内含子略多于丢失的内含子, 而在双翅目昆虫中则显示出内含子的丢失明显多于内含子的获得。该结果合理地解释了内含子在脊椎动物、线虫及昆虫中数量的分布呈下降趋势。     

双翅目昆虫复眼性特化光感受器的比较研究

雄性双翅目昆虫,包括家蝇Musca domestica、丽蝇Calliphora erythrocephala、华虻Tabanus mandarinus和憎黄虻Atylotus miser Szilady,其复眼性特化光感受器中央小网膜细胞R₇的分布从背区扩展到腹区。在雄性家蝇、华虻和憎黄虻复眼中,性特化光感受器中央小网膜细胞R₇的感杆延伸到基底膜,并同中央小网膜细胞R₈的感杆并列排列。但在雄性丽蝇复眼中,性特化光感受器中央小网膜细胞R₇的感杆不延伸到基底膜。在雌性双翅目昆虫复眼中,性特化光感受器中央小网膜细胞R₇仅仅分布在复眼的腹区,其数量比中央小网膜细胞R₈少得多。     

period基因的Thr—Gly区段在果蝇和部分双翅目昆虫中的分子进化特征

以亲缘关系极近的近缘种类群、中等距离的远缘种类群为对象,分析生物钟基因period的Thr-Gly区段的分子进化特征,发现Thr-Gly区段在果蝇和部分双翅目昆虫中未曾经历性选择和其他定向的正选择。Thr-Gly区段在果蝇nasuta亚群中的分子进化速率为10.4×10     

内蒙古阿拉善骆驼生活环境水生双翅目昆虫种类调查

【目的】通过对内蒙古阿拉善骆驼生活环境中水生双翅目昆虫的调查研究,以明确其种类的组成和分布。【方法】于2014年5-9月利用网捕法,调查了阿拉善骆驼生活环境水生双翅目昆虫。对鉴定的吸血种类的COI基因序列进行了测序和分析。【结果】共发现水生双翅目昆虫21科41属47种,其中有16种为内蒙古地区新记录,12种为吸血种类,长角亚目、芒角亚目和短角亚目个体数量分别占水生双翅目昆虫总数的49.3%,43.5%和7.2%。分子数据分析显示,12种吸血水生双翅目昆虫的COI基因序列一致性在75.9%~97.3%之间,不同科之间大部分水生双翅目昆虫差异显著,科内不同属间差异也较明显。【结论】本研究基本上掌握了内蒙古骆驼生活环境水生双翅目昆虫的种类,特别是吸血种类,为后期骆驼福斯盘尾丝虫病传播媒介种属的确定提供了基础数据。     

双翅目昆虫传粉研究进展

昆虫传粉不仅在自然生态系统中发挥着十分重要的作用,也和农业生态系统中产量密切相关。众所周知,膜翅目昆虫是最重要的传粉昆虫。双翅目昆虫分布广,物种多,数量大,也是一类十分重要的传粉昆虫,但其传粉作用未受到足够的重视。本文主要综述了双翅目传粉昆虫的主要种类、传粉效力、传粉特征、与植物的协同进化以及双翅目昆虫传粉的生态学意义。据记载双翅目昆虫中至少有71个科涉及虫媒种类,目前有资料显示访花昆虫类群中双翅目约有54 417种,按涉及的种数排序居于昆虫纲传粉昆虫目中第4位。尽管双翅目昆虫单次访问可携带花粉量相对较少(相比于膜翅目),但是较高访问速率及庞大的个体数量,保证了其作为有效传粉者的地位。传粉综合征能够有效揭示植物与传粉者的协同进化关系,尤其是对一些专化传粉现象(如五味子科-瘿蚊系统)和泛化传粉的深入研究,更加深了我们对协同进化的理解。就生态学意义而言,一方面双翅目传粉昆虫是膜翅目传粉昆虫的有益补充,另一方面在一些特殊环境中,双翅目昆虫具有不可替代的作用。当前传粉昆虫(包括双翅目)数量急剧下降,而且双翅目昆虫的传粉价值还利用较少。结合我国当前的研究现状提出了以下未来研究重点:1)加深双翅目传粉效力和适应意义的案例研究以明确双翅目昆虫在传粉体系中的地位;2)加强栖息地格局变化与昆虫多样性的研究以明确栖息地改变对昆虫的影响程度;3)梳理访花和传粉、专化传粉和泛化传粉等关系以更加明确双翅目昆虫在与植物协同进化中的作用;4)逐步深入探讨花粉浪费和花粉竞争以探究传粉策略和植物繁殖策略。这些努力将为双翅目传粉昆虫的知识普及、资源保护与利用研究等方面提供参考。     

侵染双翅目昆虫的新种,新记录,新组合及新修订

记录了最近在中国记载的侵染双翅目昆虫的虫霉目两个新种,毛蚊虫疠霉（Ｐａｎｄｏｒａｂｉｂｉｏｎｉｓ）发现于浙江元的毛蚊（Ｂｉｂｉｏｓｐ．）其初生分生孢子拟卵形,多对称１４．４～２０．５×７．２～１１．５μｍ（平均１６．５～１７．４×８．４～１０．４μｍ）Ｌ／Ｄ１．４～２．３（平均１．７～２．０）;假根２倍粗于分生包子梗,末端膨大为吸盘状固着器,休眠孢子外壁刺毛状。１９．１～２１．４μｍ,食蚜蝇干尸霉     

水生双翅目昆虫监测水体重金属污染的研究

水生双翅目昆虫是监测水体重金属污染的理想对象。文章归纳用于监测重金属污染的水生双翅目昆虫的种类,重点介绍水生双翅目昆虫在重金属污染下外部形态、内部结构、生化及分子水平的变化,以及相关生物标志物的研究,为水生双翅目昆虫用于水体重金属污染的生物监测提供科学依据。     

双翅目昆虫的婚飞

婚飞是昆虫的一个基本行为,促成远缘繁殖,对双翅目昆虫的繁殖和交配均有非常重要的意义。文中对双翅目昆虫中具有婚飞行为的类群、婚飞标志物、环境因子对婚飞的影响进行了概括总结,并特别讨论了舞虻科昆虫的婚飞行为。     

脊椎动物肾脏的比较发生和解剖

脊椎动物肾脏的比较发生和解剖陶承晞（滁州师专化生系,２３９０１２）　　在脊椎动物的胚胎发育中,肾脏的发育最为复杂。由于胚胎需要随时处理迅速发育产生的代谢废物,肾的发生很早,并历经前肾、背肾或前肾、中肾和后肾几个阶段始得完成。同时生殖系统,特别是雄形生...     

双翅目昆虫翅的退化

介绍了双翅目昆虫翅退化的5种主要类型,即短翅型、狭翅型、小翅型、弱翅型和无翅型;及翅退化双翅目昆虫的一些特殊生境诸如高原、海洋、地表以下之类。同时就双翅目昆虫翅退化的原因和机理进行了讨论。     

High rate of recent intron gain and loss in simultaneously duplicated Arabidopsis genes

We examined the gene structure of a set of 2563 Arabidopsis thaliana paralogous pairs that were duplicated simultaneously 20-60 MYA by tetraploidy. Out of a total of 23,164 introns in these genes, we found that 10,004 pairs have been conserved and 578 introns have been inserted or deleted in the time since the duplication event. This intron insertion/deletion rate of 2.7 x 10(-3) to 9.1 x 10(-4) per site per million years is high in comparison to previous studies. At least 56 introns were gained and 39 lost based on parsimony analysis of the phylogenetic distribution of these introns. We found weak evidence that genes undergoing intron gain and loss are biased with respect to gene ontology terms. Gene pairs that experienced at least 2 intron insertions or deletions show evidence of enrichment for membrane location and transport and transporter activity function. We do not find any relationship of intron flux to expression level or G + C content of the gene. Detection of a bias in the location of intron gains and losses within a gene depends on the method of measurement: an intragene method indicates that events (specifically intron losses) are biased toward the 3' end of the gene. Despite the relatively recent acquisition of these introns, we found only one case where we could identify the mechanism of intron origin--the TOUCH3 gene has experienced 2 tandem, partial, internal gene duplications that duplicated a preexisting intron and also created a novel, alternatively spliced intron that makes use of a duplicated pair of cryptic splice sites.     

Heterogeneity of intron presence/absence in Olifantiella sp. (Bacillariophyta) contributes to the understanding of intron loss

Although hypotheses have been proposed and developed to interpret the origins and functions of introns, substantial controversies remain about the mechanism of intron evolution. The availability of introns in the intermediate state is quite helpful for resolving this debate. In this study, a new strain of diatom (denominated as DB21‐1) was isolated and identified as Olifantiella sp., which possesses multiple types of 18S rDNAs (obtained from genomic DNA; lengths ranged from 2,056 bp to 2,988 bp). Based on alignments between 18S rDNAs and 18S rRNA (obtained from cDNA; 1,783 bp), seven intron insertion sites (IISs) located in the 18S rDNA were identified, each of which displayed the polymorphism of intron presence/absence. Specific primers around each IIS were designed to amplify the introns and the results indicated that introns in the same IIS varied in lengths, while terminal sequences were conserved. Our study showed that the process of intron loss happens via a series of successive steps, and each step could derive corresponding introns under intermediate states. Moreover, these results indicate that the mechanism of genomic deletion that occurs at DNA level can also lead to exact intron loss.     

Widespread intron loss suggests retrotransposon activity in ancient apicomplexans

Several facets of spliceosomal intron in apicomplexans remain mysterious. First, intron numbers vary across species by 2 orders of magnitude, indicating massive intron loss and/or gain. Second, previous studies have shown very different evolutionary patterns over different timescales, with 100-fold higher rates of intron loss/gain between genera than within genera. Third, the timing and dynamics of nearly complete intron loss in Cryptosporidium species, as well as reasons for retention of the few remaining introns, remain unknown. We compared intron positions in 785 orthologous genes between 3 moderate to intron-rich apicomplexan species. We estimate that the Theileria-Plasmodium ancestor had 4.5 times as many introns as modern Plasmodium species and 38% more than modern Theileria species, and that subsequent intron losses have outnumbered intron gains by 5.8 to 1 in Theileria and by some 56 to 1 in Plasmodium. Several patterns suggest that these intron losses occurred by recombination with reverse-transcribed mRNAs. Intriguingly, this finding suggests significant retrotransposon activity in the lineages leading to both Theileria and Plasmodium, in contrast to the dearth of known retrotransposons and intron loss within modern species from both genera. We also compared genomes from Cryptosporidium parvum and C. hominis and found no evidence of ongoing intron loss, nor of intron gain. By contrast, Cryptosporidium introns are less evolutionary conserved with Toxoplasma than are introns from other apicomplexans; thus the few remaining introns are not simply indispensable ancestral introns.     

The dynamic loss and gain of introns during the evolution of the Brassicaceae

Sequence comparison allows the detailed analysis of evolution at the nucleotide and amino acid levels, but much less information is known about the structural evolution of genes, i.e. how the number, length and distribution of introns change over time. We constructed a parsimonious model for the evolutionary rate of intron loss (IL) and intron gain (IG) within the Brassicaceae and found that IL/IG has been highly dynamic, with substantial differences between and even within lineages. The divergence of the Brassicaceae lineages I and II marked a dramatic change in the IL rate, with the common ancestor of lineage I losing introns three times more rapidly than the common ancestor of lineage II. Our data also indicate a subsequent declining trend in the rate of IL, although in Arabidopsis thaliana introns continue to be lost at approximately the ancestral rate. Variations in the rate of IL/IG within lineage II have been even more remarkable. Brassica rapa appears to have lost introns approximately 15 times more rapidly than the common ancestor of B. rapa and Schenkiella parvula, and approximately 25 times more rapidly than its sister species Eutrema salsugineum. Microhomology was detected at the splice sites of several dynamic introns suggesting that the non‐homologous end‐joining and double‐strand break repair is a common pathway underlying IL/IG in these species. We also detected molecular signatures typical of mRNA‐mediated IL, but only in B. rapa.     

Rare genomic characters do not support Coelomata: intron loss/gain

Recently, a new phylogenetic method employing intron positionsharing across species was proposed and support for a Coelomateclade reported (Zheng et al. 2007. A rigorous analysis of thepattern of intron conservation supports the Coelomata cladeof animals. Mol Biol Evol. 24:2583–2592.). Here, we showthat the previous analysis depends on: 1) an idiosyncratic definitionof "conserved" introns, 2) exclusion of all phylogeneticallyinformative introns present in outgroups, 3) incorrect inferenceof change along the critical branch, and 4) lack of variationin rates across branches. The method thus seems unlikely togive accurate results. In addition, we address differences inrates of loss across intron sites, which Zheng et al. claimedinvalidates our previous analysis that supported Ecdysozoa (Royand Gilbert. 2005a. Resolution of a deep animal divergence bythe pattern of intron conservation. Proc Natl Acad Sci USA.102:4403–4408.). Instead, we show that our conclusionsare likely to be robust to such concerns.     

The biology of intron gain and loss

Intron density in eukaryote genomes varies by more than three orders of magnitude, so there must have been extensive intron gain and/or intron loss during evolution. A favored and partial explanation for this range of intron densities has been that introns have accumulated stochastically in large eukaryote genomes during their evolution from an intron-poor ancestor. However, recent studies have shown that some eukaryotes lost many introns, whereas others accumulated and/or gained many introns. In this article, we discuss the growing evidence that these differences are subject to selection acting on introns depending on the biology of the organism and the gene involved.     

Investigation of loss and gain of introns in the compact genomes of pufferfishes (Fugu and Tetraodon)

We have investigated intron evolution in the compact genomes of 2 closely related species of pufferfishes, Fugu rubripes and Tetraodon nigroviridis, that diverged about 32 million years ago (MYA). Analysis of 148,028 aligned intron positions in 13,547 gene pairs using human as an outgroup identified 57 and 24 intron losses in Tetraodon and fugu lineages, respectively, and no gain in either lineage. For comparison, we analyzed 144,545 intron positions in 12,866 orthologous pairs of genes in human and mouse that diverged about 61 MYA using dog as an outgroup and identified 51 intron losses in mouse and 3 losses in human and no gain. The rate of intron loss in Tetraodon is higher than that in fugu, mouse, and human but lower than the previous estimates for other eukaryotes. The introns lost in pufferfishes and mammals are significantly shorter than the mean size of introns in the genome. One intron deleted in fugu and another in Tetraodon have left behind 6 and 3 nucleotides, respectively, suggesting that they were lost due to genomic deletions. Such losses of introns are likely to be the result of a higher rate of DNA deletions experienced by the genomes of pufferfishes compared with mammals. The shorter generation time of Tetraodon compared with fugu, and the rich diversity and higher activity of transposable elements in pufferfishes compared with mammals, may be responsible for the higher rate of intron loss in Tetraodon. Our findings indicate that overall very little intron turnover has occurred in pufferfishes and mammals during recent evolution and that intron gain is an extremely rare event in vertebrate evolution.