首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
Abstract

The oligochaete family Lumbriculidae is well represented in the Northern Hemisphere, but for the Southern Hemisphere only Lumbriculus variegatus (Müller) is recorded, from Africa, Australia, and New Zealand; no species are known from South America (Brinkhurst & Jamieson 1971). According to Brinkhurst (1971), L. variegatus may be a recent introduction to New Zealand, where it is now widely distributed in a range of inland waters.  相似文献   

3.
Primula cuneifolia Ledeb. (Primulaceae), we analyzed intraspecific variation of the nucleotide sequences of non-coding regions of chloroplast DNA: the intergenic spacers between trnT (UGU) and the trnL (UAA) 5′exon, the trnL (UAA) 3′exon and trnF (GAA), and atpB and rbcL. In 20 populations of P. cuneifolia, 22 nucleotide substitutions and five insertions/deletions were inferred, and their genetic distances ranged from 0.001 to 0.008. Eight distinct haplotypes could be recognized and each haplotype was found to be geographically structured. Three major clades (the Northern, Hokkaido and Southern clades) were revealed in phylogenetic analyses of the haplotypes. The haplotypes of the Northern clade had a wider distribution area in the populations of Mt. Rausu and Rishiri Island of eastern and northern Hokkaido in Japan, northward to Unalaska Island in the Aleutians, and those of the Hokkaido clade were distributed in the populations of central Hokkaido and Mt. Iwaki of the northern Honshu in Japan; in addition, those of the Southern clade were observed only in the populations of the central Honshu. It was shown that the genetic diversifications of the Southern clade were higher than those of the Northern and Hokkaido clades. Furthermore, it was shown that the topology within the Southern clade was hierarchical, and the haplotypes of the Southern populations in the clade were derivative. From these results, we concluded that the cpDNA haplotypes of the three clades in P. cuneifolia arose and assumed the present distribution areas through several cycles of glacial advance and retreat in the Pleistocene. Received 24 June 1998/ Accepted in revised form 28 December 1998  相似文献   

4.
Variations of the shape and polarity of the DNA grooves caused by changes of the DNA conformation play an important role in the DNA readout. Despite the fact that non-canonical trans and gauche- conformations of the DNA backbone angle γ (O5′–C5′–C4′–C3′) are frequently found in the DNA crystal structures, their possible role in the DNA recognition has not been studied systematically. In order to fill in this gap, we analyze the available high-resolution crystal structures of the naked and complexed DNA. The analysis shows that the non-canonical γ angle conformations are present both in the naked and bound DNA, more often in the bound vs. naked DNA, and in the nucleotides with the A-like vs. the B-like sugar pucker. The alternative angle γ torsions are more frequently observed in the purines with the A-like sugar pucker and in the pyrimidines with the B-like sugar conformation. The minor groove of the nucleotides with non-canonical γ angle conformation is more polar, while the major groove is more hydrophobic than in the nucleotides with the classical γ torsions due to variations in exposure of the polar and hydrophobic groups of the DNA backbone. The propensity of the nucleotides with different γ angle conformations to participate in the protein–nucleic acid contacts in the minor and major grooves is connected with their sugar pucker and sequence-specific. Our findings imply that the angle γ transitions contribute to the process of the protein–DNA recognition due to modification of the polar/hydrophobic profile of the DNA grooves.  相似文献   

5.
Abstract

Bicyclonucleosides bearing a 5-deoxy-5-N-hydroxyamino-3,N 5-(1,1-ethano)-β-o-furanosyl sugar moiety (15–18) have been prepared by glycosidation of the corresponding bicyclosugars obtained via an intramolecular reverse Cope elimination. The configuration of the asymmetric carbon of the 1,1-ethano bridge is the most important factor directing the conformation of the N-hydroxypyrrolidine ring and its invertomers ratio as shown by variable temperature H NMR experiments.  相似文献   

6.
The taxonomic and evolutionary affinities of Southern hemisphere smooth‐shelled blue mussels are unclear, with studies using different marker types having identified different relationships among various geographic regions. Using an existing and a new molecular assay, the present study builds on previous work to test the distribution of blue mussels native to and introduced to the Southern hemisphere. Populations of Mytilus were sampled from New Zealand, Australia, and Chile. The nuclear‐DNA marker Me 15/16 was used to identify the taxonomic status of 484 individuals. A new restriction fragment length polymorphism (RFLP) assay was used to identify the hemisphere of origin for a subset of Mytilus galloprovincialis. The Me15/16 marker identified 478 pure M. galloprovincialis from Southern hemisphere sites and six Mytilus edulis/M. galloprovincialis hybrids from the Auckland Islands (New Zealand) and Chile. A cytoplasmic RFLP identified Northern hemisphere M. galloprovincialis in almost every Southern hemisphere region. The presence of native M. galloprovincialis at high latitudes (up to 52°S) has implications for our understanding of environmentally induced selective constraints considered to determine species distributions. Widespread occurrence of invasive Northern hemisphere blue mussels in the Southern hemisphere is documented for the first time. Identification of inter‐specific hybrids (M. edulis × M. galloprovincialis) in Chile and in the Auckland Islands (subantarctic New Zealand) illustrates that environments ranging from international ports to remote protected locations are vulnerable to bioinvasion. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 898–909.  相似文献   

7.
Global phylogeographic patterns in Sanionia uncinata are addressed based on information in internal transcribed spacer (ITS) (214 specimens) and the plastid markers trnLtrnF (221) and rpl16 (217). ITS suggests a monophyletic Sanionia and a paraphyletic S. uncinata; this was neither supported nor rejected by plastid data. Northern or Eastern Eurasia and Alaska appear important in the early evolution of Sanionia and some populations dispersed into the Southern Hemisphere relatively early. Some haplotypes or groups of haplotypes are morphologically and ecologically distinct, biologically meaningful units that correspond with S. orthothecioides, S. symmetrica and S. georgicouncinata s.l. The latter includes two species that are indistinguishable by morphology, S. georgicouncinata s.s. (Southern Hemisphere) and S. nivalis (Northern Hemisphere). Tropical African and South American S. uncinata populations have separate origins and the Southern Hemisphere was colonized at least twice. In the northern circum‐Arctic region, the haplotype composition differs between the North Atlantic and Beringian areas. Eastern Eurasia has a higher S. uncinata haplotype diversity than other Holarctic regions, implying less devastating effects of recurrent glacial periods. For Eastern and Western Eurasia, North America and the Southern Hemisphere, most of the haplotype variation was found within the regions, but 14–18% can be referred to among region variation. Plastid haplotype diversity was lower in the Southern Hemisphere than in the Arctic to subarctic, possibly attributable to founder effects. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 168 , 19–42.  相似文献   

8.

Two novel C-linked oxadiazole carboxamide nucleosides 5-(2′-deoxy-3′,5′-β-D-erythro-pentofuranosyl)-1,2,4-oxadiazole-5-carboxamide (1) and 5-(2′-deoxy-3′,5′-β-D-erythro-pentofuranosyl)-1,2,4-oxadiazole-3-carboxamide (2) were successfully synthesized and characterized by X-ray crystallography. The crystallographic analysis shows that both unnatural nucleoside analogs 1 and 2 adapt the C2′-endo (“south”) conformation. The orientation of the oxadiazole carboxamide nucleobase moiety was determined as anti (conformer A) and high anti (conformer B) in the case of the nucleoside analog 1 whereas the syn conformation is adapted by the unnatural nucleoside 2. Furthermore, nucleoside analogs 1 and 2 were converted with high efficiency to corresponding nucleoside triphosphates through the combination chemo-enzymatic approach. Oxadiazole carboxamide deoxyribonucleoside analogs represent valuable tools to study DNA polymerase recognition, fidelity of nucleotide incorporation, and extension.

  相似文献   

9.
10.
Alzheimer’s disease (AD) is a progressive neurodegenerative disorder that is characterized by loss of intellectual functioning of brain and memory loss. According to amyloid cascade hypothesis, aggregation of amyloid-β42 (Aβ42) peptide can generate toxic oligomers and their accumulation in the brain is responsible for the onset of AD. In spite of carrying out a large number of experimental studies on inhibition of Aβ42 aggregation by small molecules, the detailed inhibitory mechanism remains elusive. In the present study, comparable molecular dynamics (MD) simulations were performed to elucidate the inhibitory mechanism of a sulfonamide inhibitor C1 (2,5-dichloro-N-(4-piperidinophenyl)-3-thiophenesulfonamide), reported for its in vitro and in vivo anti-aggregation activity against Aβ42. MD simulations reveal that C1 stabilizes native α-helix conformation of Aβ42 by interacting with key residues in the central helix region (13–26) with hydrogen bonds and ππ interactions. C1 lowers the solvent-accessible surface area of the central hydrophobic core (CHC), KLVFF (16–20), that confirms burial of hydrophobic residues leading to the dominance of helical conformation in the CHC region. The binding free energy analysis with MM–PBSA demonstrates that Ala2, Phe4, Tyr10, Gln15, Lys16, Leu17, Val18, Phe19, Phe20, Glu22, and Met35 contribute maximum to binding free energy (?43.1 kcal/mol) between C1 and Aβ42 monomer. Overall, MD simulations reveal that C1 inhibits Aβ42 aggregation by stabilizing native helical conformation and inhibiting the formation of aggregation-prone β-sheet conformation. The present results will shed light on the underlying inhibitory mechanism of small molecules that show potential in vitro anti-aggregation activity against Aβ42.  相似文献   

11.
Abstract

A review of the distribution of toxic dinoflagellates and related toxic events in the Mediterranean Sea is provided. Diarrhetic shellfish poisoning (DSP) and paralytic shellfish poisoning (PSP) are the main seafood contaminations, that have been reported since 1987. In 1994 four lethal cases for PSP were reported in Morocco. DSP seems to be restricted in the Northern part of the basin, while PSP contamination presents a wider distribution. Potentially DSP species, belonging to the genus Dinophysis, are widely distributed in the Mediterranean Sea, suggesting a wider extension of this contamination. The lack of monitoring programs in the Southern Mediterranean could be responsible of DSP overlooking. The species responsible for PSP are Gymnodinium catenatum in the Alboran Sea and Alexandrium minutum in various parts of the basin. Ichtyotoxic effects, due to Gymnodinium and Gyrodinium species, have been sporadically reported in some Mediterranean areas.  相似文献   

12.
Abstract

Air-borne pollen census in Messina in the years 1985–1986 - Pollen of 20 herbs and weeds, and that of 14 trees or shrubs, were identified in the air of Messina (Southern Italy), in the years 1985–1986. The relative frequencies were correlated with climatic factors affecting the pollen diffusion in the studied area.  相似文献   

13.
The accurate delimitation of evolutionary population units represents an important component in phylogeographic and conservation genetic studies. Here, we used a combined population assignment and historical demographic approach to study a complex of ecomorphologically distinctive populations of Black Salamanders (Aneides flavipunctatus) that are parapatrically distributed and meet at a three‐way contact zone in north‐western California. We used mitochondrial tree‐based and multilocus clustering methods to evaluate a priori two‐ (Northern and Southern) and three (Northern, Coast and Inland) population hypotheses derived from previous studies. Mitochondrial results were consistent with the two‐ and three‐population hypotheses, while the nDNA clustering results supported only the two‐population hypothesis. Historical demographic analyses and mtDNA gene divergence estimates revealed that the Northern and Southern populations split during the Pliocene (2–5 Ma). Subdivision of the Southern population into Coast and Inland populations was estimated to be late Pleistocene (0.24 Ma), although our mtDNA results suggested a Pliocene divergence. Effective gene flow estimates (2Nem) suggest that either the two‐ or three‐population hypotheses remain valid. However, our results unexpectedly revealed that the Northern population might instead represent two parapatric populations that separated nearly 4 Ma. These results are surprising because the Pliocene divergence between these ecomorphologically conservative forms is similar or older than for the ecomorphologically divergent Coast and Inland sister populations. We conclude that Black Salamanders in north‐western California belong to at least three or four populations or species, and these all meet criteria for being Evolutionary Significant Units or ‘ESUs’ and therefore warrant conservation consideration.  相似文献   

14.
Capsule: The second national survey of Twite Linaria flavirostris estimated a UK breeding population of 7831 pairs (95% confidence limits: 5829–10?137) in 2013.

Aims: To estimate the breeding population size of Twite in the UK and constituent countries and to calculate change since the 1999 survey.

Methods: Counts of Twite were made on three visits between May and July across a stratified random sample of 1-km squares in England, Scotland and Wales. In Northern Ireland, a complete census was made of the known range and adjacent 1-km squares with suitable habitat. Field surveys involved walking line transects 200 m apart and, in suitable nesting habitat, making 5-minute stops at 100 m intervals to scan and listen for Twite.

Results: The UK population of Twite was estimated at 7831 pairs (95% CL: 5829–10?137). This was 21% lower but not significantly different from the 1999 survey estimate. Scotland held 98% of the UK population (7640, 95% CL: 5629–9954). There were an estimated 164 pairs (95% CL: 76–297) in England, a significant decline of 72% from 1999. Estimated totals for Wales and Northern Ireland were 16 (95% CL: 10–24) and 18 pairs respectively.

Conclusion: The second national survey suggests a moderate decline in the UK Twite population since 1999 but with considerable variation between countries. Further work is required to understand the drivers of population change across breeding populations.  相似文献   

15.
Abstract

A novel proton transfer compound (HMeOABT)?+?(HDPC)? (1) and its Fe(III), Co(II), Ni(II) and Cu(II) complexes (25) have been prepared and characterized by spectroscopic techniques. Complex 4 has distorted octahedral conformation revealed by single crystal X-ray diffraction method. Structures of the other complexes might be proposed as octahedral according to experimental data. All compounds were also evaluated for their in vitro inhibition effects on hCA I and II for their hydratase and esterase activities. Although there is no inhibition for hydratase activities, all compounds have inhibited the esterase activities of hCA I and II. Data have been analyzed by using a one-way analysis of variance. The comparison of the inhibition studies of 15 to parent compounds indicates that 15 have superior inhibitory effects. The inhibition effects of 25 are also compared to inhibitory properties of the metal complexes of MeOABT and H2DPC, revealing an improved transfection profile.  相似文献   

16.
This work analysis the length-weight relationships for fish species captured by artisanal fishery along the continental coast of Ecuador. Fishermen used the following fishing gear: beach seine nets (5.1–31.8 mm), shrimp trawl nets (21.8–31.8 mm) and bottom gill nets (54.1–203.2 mm). Sampling took place during the years 2012 and 2014. Frequency of sampling was monthly, and it was completed systematically from Southern toward Northern Provinces. Length-weight relationship (LWR) was realized by the power model (y = a × xb), for species with a bivariate dataset >70. A total of 59 commercial and 15 non-commercial species were registered. For 74 species, our analysis including a higher total length not reported in LWR estimates previously. The determination coefficient (r2) value was always above 0.95.  相似文献   

17.
Brandano, M. & Policicchio, G. 2011: Strontium stratigraphy of the Burdigalian transgression in the Western Mediterranean. Lethaia, Vol. 45, pp. 315–328. A 87Sr/86Sr analysis of selected pectinid shells has been performed to refine the stratigraphical framework of the Burdigalian transgressive event. Samples were collected from shallow water successions of the Western Mediterranean area (North‐Eastern Sardinia, Southern Corsica, Central Apennines). The Western Mediterranean is the result of the interaction between the European and the African plates. Sardinia and Corsica were extended and rifted apart from the Iberian Peninsula during the opening of the Liguro‐Provencal basin, between 30 and 15 Ma. In the outcrops of Northern Sardinia and Southern Corsica, Burdigalian deposits nonconformably overlie Varisican granites. In the central Apennines the Burdigalian deposits paraconformably overlie the Cretaceous platform. These are transgressive deposits, characterized by the presence of Miogypsina globulina, which points out early to middle Burdigalian age. The Sr isotope ages indicate that marine transgression in Northern Sardina and Southern Corsica took place between 18.6 and 18.3 Ma, which could correspond to the eustatic sea level rise of the Bur3 third‐order sequence. In the Central Apennines the Burdigalian transgression was anticipated (18.8 Ma) by subsidence input linked to the eastward migration of the orogenic system. This input allowed the Miocene carbonate ramp to develop on the Cretaceous platform substrate, while successive eustatic rise controlled the evolution of the stratigraphical architecture. The following regressive phase is recorded in both the Apennine and Corsica successions. The end of this phase is dated between 17.6 and 17.5 Ma and corresponds to sea level drop corresponding to the occurrence of the Mi 1b event. □Burdigalian, pectinids, strontium stratigraphy, transgression, Western Mediterranean  相似文献   

18.
ABSTRACT.
  • 1 The population biology of Anthocharis cardamines (L.) is described and shown to vary with locality. Southern and Western populations emerge earlier than Northern ones, but Western and Northern populations occupy similar, wetter habitats and are associated primarily with Cardamine pratensis (L.). Southern populations are recorded mostly from Alliaria petiolata (Bieb.).
  • 2 Studies on egg and larval survival indicate that host plant-induced death and parasitization by a tachinid are important mortality factors. However, a key-factor analysis on one population indicates that the major determinant of population size may be the number of eggs laid by ovipositing females, itself dependent upon weather during the oviposition period. Populations in different localities do show similar trends in abundance, corroborating the effect of weather.
  • 3 Human effects on distribution and abundance are discussed, and some conservation strategies suggested.
  相似文献   

19.
Two new species of the Empis (Leptempis) rustica group are described: E. (L.) tenuis n. sp. and E. (L.) lauriauti n. sp. Both were mainly collected in mountainous areas of the Mediterranean basin; the first species was collected in Morocco and Southern Spain; the latter was found in late summer in the Southern Alps in France. The key to species of the Empis (L.) rustica group is updated to include these two new species as well as a recently described Caucasian species.  相似文献   

20.
Paracetamol, sulfathiazole and l-glutamic acid are presented as examples of pharmaceutical crystal polymorphic systems. The effect of N-acylated sulfathiazole derivatives (3–6) on sulfathiazole crystallisation is discussed, and possible modes of action presented. Methods for the control of the crystal polymorphism of l-glutamic acid which utilise the principles of conformation mimicry and co-operative binding are presented. The preparation of a series of bis-amides of EDTA derived from sulfathiazole, 5-aminoisophthalic acid and 4-hydroxyaniline (i.e. compounds 9a–c) is presented, as is data on the effect of these compounds on the crystallisation of, respectively, sulfathiazole, l-glutamic acid and paracetamol.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号