Escalation of a coevolutionary arms race through host rejection of brood parasitic young

Cuckoo nestlings that evict all other young from the nest soon after hatching impose a high reproductive cost on their hosts. In defence, hosts have coevolved strategies to prevent brood parasitism. Puzzlingly, they do not extend beyond the egg stage. Thus, hosts adept at recognizing foreign eggs remain vulnerable to exploitation by cuckoo nestlings. Here we show that the breach of host egg defences by cuckoos creates a new stage in the coevolutionary cycle. We found that defences used during the egg-laying period by host superb fairy-wrens (Malurus cyaneus) are easily evaded by the Horsfield's bronze-cuckoo (Chrysococcyx basalis), a specialist fairy-wren brood parasite. However, although hosts never deserted their own broods, they later abandoned 40% of nests containing a lone Horsfield's bronze-cuckoo nestling, and 100% of nests with a lone shining bronze-cuckoo nestling (Chrysococcyx lucidus), an occasional fairy-wren brood parasite. Our experiments demonstrate that host discrimination against evictor-cuckoo nestlings is possible, and suggest that it has selected for the evolution of nestling mimicry in bronze-cuckoos.     

A brood parasitic catfish of mouthbrooding cichlid fishes in Lake Tanganyika

Brood parasitism, where a brood of the parasitic species is fostered by the parents of another species, is well known among birds. In most cases, such offspring show a complete reliance upon their host parents for food, protection and warmth until their independence. In other vertebrate groups, however, such total dependence upon a host species is unknown. I report here the first example of true brood parasitic behaviour discovered among fishes. In Lake Tanganyika, an endemic mochokid catfish, Synodontis multipunctatus Boulenger, is a brood parasite of mouthbrooding fishes of the family Cichlidae. The eggs of the catfish are incubated in the mouths of any of several host species together with the host's eggs, but hatch earlier. Following absorption of their yolk sacs, the catfish fry feed upon the fry of the host while still in its mouth. Thus the early stages of development of this catfish not only depend upon their hosts for food and protection, but exploit almost their entire parental investment.     

松树体内寄生线虫种类及其致病性

松树是我国重要的造林先锋树种与景观绿化树种,然而,近年来在许多地方发现有不明原因、不同症状的枯萎松树,不同种类的寄生线虫在枯萎松树中被发现.笔者对松树体内的寄生线虫以及这些寄生线虫的致病性进行了综述.到目前为止,在我国松树上已经发现寄生线虫有11属42种以及11个未定种.除松材线虫外,一些线虫如拟松材线虫、Bursaphelenchus sexdentati等也能够引起某些松树的死亡.     

Plant genetics: gene transfer from parasitic to host plants

Plant mitochondrial genes are transmitted horizontally across mating barriers with surprising frequency, but the mechanism of transfer is unclear. Here we describe two new cases of horizontal gene transfer, from parasitic flowering plants to their host flowering plants, and present phylogenetic and biogeographic evidence that this occurred as a result of direct physical contact between the two. Our findings complement the discovery that genes can be transferred in the opposite direction, from host to parasite plant.     

Speciation by hybridization in Heliconius butterflies

Speciation is generally regarded to result from the splitting of a single lineage. An alternative is hybrid speciation, considered to be extremely rare, in which two distinct lineages contribute genes to a daughter species. Here we show that a hybrid trait in an animal species can directly cause reproductive isolation. The butterfly species Heliconius heurippa is known to have an intermediate morphology and a hybrid genome, and we have recreated its intermediate wing colour and pattern through laboratory crosses between H. melpomene, H. cydno and their F1 hybrids. We then used mate preference experiments to show that the phenotype of H. heurippa reproductively isolates it from both parental species. There is strong assortative mating between all three species, and in H. heurippa the wing pattern and colour elements derived from H. melpomene and H. cydno are both critical for mate recognition by males.     

固相吸附-原子吸收光谱法测定党参中铜的形态

建立了LSA-10吸附树脂固相吸附、原子吸收光谱法测定党参中微量铜的形态的方法.将党参中铜的形态划分为无机态、有机态和残渣态,每克党参中铜的总量为26.485μg,铜元素的回收率在94%～102%内.通过对党参中铜的总量和各形态分布的对比,得出铜的富集和分布的基本规律.     

基于主客体间竞争键合的荧光开关的构筑

通过四磺化-二(1,5-萘二酚)-32-冠-8-四钠盐(H)与荧光分子(G1)之间弱相互作用(π-π堆积以及静电吸引)的协同效应,构筑了荧光增强的水溶性准二轮烷G1?H,而4,4’-联吡啶鎓双阳离子(G2)与主体H的竞争键合使G1?H解离的同时形成了新的准二轮烷G2?H,在此过程中,伴随着G1荧光的淬灭。因此,G1?H可作为受体/指示剂传感体系实现对G2的可视化传感。     

Speciation of iron in atmospheric particulate matter by EXAFS

In the atmospheric particulate matter (PM), fractions with a particle size of less than 10 μm (PM10) or evenless than 2.5 μm (PM2.5) in aerodynamic diameter can be inhaled into human body and cause serious health problems[1,2]. The influence of the PM on health is not only related to elemental concentrations, but also to its chemical speciation. The study on elemental speciation in atmospheric PM is significant for evaluating toxicity of PM and providing information about the formation a…     

Speciation in a ring

The evolutionary divergence of a single species into two has never been directly observed in nature, primarily because speciation can take a long time to occur. A ring species, in which a chain of intergrading populations encircles a barrier and the terminal forms coexist without interbreeding, provides a situation in which variation in space can be used to infer variation in time. Here we reconstruct the pathway to speciation between two reproductively isolated forms of greenish warbler (Phylloscopus trochiloides). These two taxa do not interbreed in central Siberia but are connected by a long chain of intergrading populations encircling the Tibetan Plateau to the south. Molecular data and climatic history imply that the reproductively isolated taxa came into contact following expansions northward around the western and eastern sides of the plateau. Parallel selection pressures for increased song complexity during the northward expansions have been accompanied by divergence in song structure. Playback experiments show that the two Siberian forms do not recognize each other's songs. Our results show how gradual divergence in a trait involved in mate choice leads to the formation of new species.     

Gene replacement in parasitic protozoa

Trypanosomatid protozoa frequently cause severe diseases in humans. Many molecules likely to have a role during the infectious cycle have been identified, yet proof of their function is often lacking. We describe studies in Leishmania major of homologous gene targeting, a powerful method for testing gene function in other organisms. Following introduction of a construct containing dihydrofolate reductase-thymidylate synthase (dhfr-ts) flanking sequences fused to neomycin phosphotransferase, 45% of the colonies contained the planned homologous replacement; this frequency rose to nearly 100% in transfections using low amounts of DNA. Integrative transfection in Leishmania thus resembles that of Saccharomyces cerevisiae in giving predominantly homologous events. To facilitate studies of folate metabolism and chemotherapy the sole dhfr-ts copy in a heterozygous deletion line was replaced, yielding lines that were functionally DHFR-TS-. Although most genes are diploid in trypanosomatids, methods exploiting the high frequency of homologous recombination should permit complete replacement of any parasite gene.     

Al-Ferron逐时络合比色分光光度法分析Al30形态的研究

探讨了运用Al—Ferron逐时络合比色分光光度法进行Al30分析的适用性．与传统ferron比色法属于操作性的定义不同．该方法对Al-Ferron逐时络合比色的时间扫描数据进行非线性拟合,并假定3种动力学可测形态：一种是瞬时完成的0级反应的铝单体：另两种是一级反应的待定形态．以拟舍得到的特征k值和吸光度,作为定性和定量的依据．结果表明：通过优化拟合改进的ferron比色法,可以获得Al30的特征k值,其值在15mLferron比色体系中为7×10-5数量级;Al30用ferron比色法的定量分析结果与^27Al NMR鉴定结果基本一致,可用以定量分析Al30.该方法既可替代昂贵的^27Al NMR鉴定．又能弥补传统ferron比色法定性模糊的不足．     

Speciation through sensory drive in cichlid fish

Theoretically, divergent selection on sensory systems can cause speciation through sensory drive. However, empirical evidence is rare and incomplete. Here we demonstrate sensory drive speciation within island populations of cichlid fish. We identify the ecological and molecular basis of divergent evolution in the cichlid visual system, demonstrate associated divergence in male colouration and female preferences, and show subsequent differentiation at neutral loci, indicating reproductive isolation. Evidence is replicated in several pairs of sympatric populations and species. Variation in the slope of the environmental gradients explains variation in the progress towards speciation: speciation occurs on all but the steepest gradients. This is the most complete demonstration so far of speciation through sensory drive without geographical isolation. Our results also provide a mechanistic explanation for the collapse of cichlid fish species diversity during the anthropogenic eutrophication of Lake Victoria.     

Hedgehog regulates smoothened activity by inducing a conformational switch

Hedgehog (HH) morphogen is essential for metazoan development. The seven-transmembrane protein smoothened (SMO) transduces the HH signal across the plasma membrane, but how SMO is activated remains poorly understood. In Drosophila melanogaster, HH induces phosphorylation at multiple Ser/Thr residues in the SMO carboxy-terminal cytoplasmic tail, leading to its cell surface accumulation and activation. Here we provide evidence that phosphorylation activates SMO by inducing a conformational switch. This occurs by antagonizing multiple Arg clusters in the SMO cytoplasmic tail. The Arg clusters inhibit SMO by blocking its cell surface expression and keeping it in an inactive conformation that is maintained by intramolecular electrostatic interactions. HH-induced phosphorylation disrupts the interaction, and induces a conformational switch and dimerization of SMO cytoplasmic tails, which is essential for pathway activation. Increasing the number of mutations in the Arg clusters progressively activates SMO. Hence, by employing multiple Arg clusters as inhibitory elements counteracted by differential phosphorylation, SMO acts as a rheostat to translate graded HH signals into distinct responses.     

寄生传输中的抗干扰研究

本文讨论了寄生传输中干扰的特点及抗干扰的有效途径,给出了软件抗干扰的编码方式,可直接应用于系统的工程设计中。     

环境中汞的形态分析

从环境中汞的存在形态出发,按测定方法进行分类;综述了近几年来汞的形态分析方法,并对各种方法进行了比较.     

环境样品中无机铬的形态分析

本文综述了近年来无机铬形态分析新进展,比较了各类分析方法的特点,提出本领域的研究方向.     

Receptor binding redefined by a structural switch in a mutant human insulin

Crystal structures of insulin have been determined in various distinct forms, the relevance of which to receptor recognition has long been the subject of speculation. Recently the crystal structure of an inactive insulin analogue has been determined and, surprisingly, found to have a conformation identical to native insulin. On this basis Dodson and colleagues have suggested that the known insulin crystal structures reflect an inactive conformation, and that a change in conformation is required for activity--specifically, the carboxy terminal residues of the B-chain are proposed to separate from the amino terminal residues of the A-chain. Here we report the solution structure of an active insulin mutant, determined by two-dimensional NMR, which supports this hypothesis. In the mutant, the carboxy terminal beta-turn and beta-strand of the B-chain are destabilized and do not pack across the rest of the molecule. We suggest that analogous detachment of the carboxy terminal region of the B-chain occurs in native insulin on binding to its receptor. Our finding that partial unfolding of the B-chain exposes an alternative protein surface rationalizes the receptor-binding properties of a series of anomalous insulin analogues, including a mutant insulin associated with diabetes mellitus in man.