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排序方式: 共有692条查询结果,搜索用时 281 毫秒
91.
Andrés Baselga Jorge M. Lobo Jens‐Christian Svenning Miguel B. Araújo 《Journal of Biogeography》2012,39(4):760-771
Aim Do species range shapes follow general patterns? If so, what mechanisms underlie those patterns? We show for 11,582 species from a variety of taxa across the world that most species have similar latitudinal and longitudinal ranges. We then seek to disentangle the roles of climate, extrinsic dispersal limitation (e.g. barriers) and intrinsic dispersal limitation (reflecting a species’ ability to disperse) as constraints of species range shape. We also assess the relationship between range size and shape. Location Global. Methods Range shape patterns were measured as the slope of the regression of latitudinal species ranges against longitudinal ranges for each taxon and continent, and as the coefficient of determination measuring the degree of scattering of species ranges from the 1:1 line (i.e. latitudinal range = longitudinal range). Two major competing hypotheses explaining species distributions (i.e. dispersal or climatic determinism) were explored. To this end, we compared the observed slopes and coefficients of determination with those predicted by a climatic null model that estimates the potential range shapes in the absence of dispersal limitation. The predictions compared were that species distribution shapes are determined purely by (1) intrinsic dispersal limitation, (2) extrinsic dispersal limitations such as topographic barriers, and (3) climate. Results Using this methodology, we show for a wide variety of taxa across the globe that species generally have very similar latitudinal and longitudinal ranges. However, neither neutral models assuming random but spatially constrained dispersal, nor models assuming climatic control of species distributions describe range shapes adequately. The empirical relationship between the latitudinal and longitudinal ranges of species falls between the predictions of these competing models. Main conclusions We propose that this pattern arises from the combined effect of macroclimate and intrinsic dispersal limitation, the latter being the major determinant among restricted‐range species. Hence, accurately projecting the impact of climate change onto species ranges will require a solid understanding of how climate and dispersal jointly control species ranges. 相似文献
92.
Localization of eukaryotic initiation factor 2 in neuron primary cultures and established cell lines
Maria V. T. Lobo F. Javier M. Alonso Susana Rodriguez Alberto Alcazar Elena Martin Francisco Munoz Rafael G-Santander Matilde Salinas Juan L. Fando 《The Histochemical journal》1997,29(6):453-468
Eukaryotic initiation factor 2 (eIF-2) is a heterotrimeric protein with subunits α, β and γ that forms a ternary complex with
Met-tRNA and GTP. It promotes the binding of Met-tRNA to ribosomes and controls translational rates via phosphorylation/dephosphorylation
mechanisms. By means of immunofluorescence and post-embedding immunocytochemistry of intact cells and quantitative immunoblotting
of cell extracts, the cellular distribution of the initiation factor has been examined in primary neuronal cultures as well
as in two established cell lines: PC12 phaeochromocytoma cells and rat pituitary GH4C1 cells. Our results indicated that the
initiation factor is located not only in the cytoplasm but also in the nuclei of the cultured neurons and cell lines. In the
cytoplasm, immunocytochemical studies reveal that the factor is present mainly in those areas that are rich in ribosomes.
In the nucleus, the immunolabelling of eukaryotic initiation factor 2 verified the presence of gold particles in both nucleolar
and extranucleolar areas. The specific distribution of this factor on both sides of the nuclear envelope suggests that it
might have some nuclear-related function(s) besides its already known role in the control of translation 相似文献
93.
94.
95.
We determined the incidence of curculionid beetles of the genus Lonchophorus on aborted and not aborted flower buds and developing fruits of the tree Ceiba pentandra in southeastern Costa Rica. Beetle larvae were found in reproductive parts of all trees sampled trees. The frequency of beetle
larvae was greater in aborted buds and immature fruits. A positive correlation between larvae development and flower bud development
indicates that female oviposition occurred in an early flower developmental stage and time until bud abortion is variable.
Weevil herbivory could be considered as one of the main factors that cause flower bud and fruit abortion in C. pentandra.
Resumen Determinamos la incidencia de curculiónidos del género Lonchophorus en botones florales y frutos inmaduros tanto abortados como no abortados en el árbol Ceiba pentandra en el SE de Costa Rica. Las larvas de curculiónidos fueron encontradas en todos los árboles muestreados. La frecuencia de larvas fue mayor en botones y frutos abortados. Una correlación positiva entre el desarrollo larval y el desarrollo del botón indica que la oviposición ocurre en una fase temprana de este y que el tiempo hasta el aborto es variable. La herbivoría por larvas de curculiónidos puede ser uno de los factores más importantes en el aborto de botones y frutos inmaduros en C. pentandra.相似文献
96.
97.
Daniela Peixoto Elisabete P. Ferreira Ana M. Lourenço Jordan L. Johnson Ana M. Lobo Prasad L. Polavarapu 《Chirality》2018,30(7):932-942
(R)‐Metacycloprodigiosin can exist in three different tautomeric forms, each with hydrogens at C9′ and C12 in syn or anti orientation. With the addition of HCl, this structural diversity reduces to syn‐(R)‐metacycloprodigiosin‐HCl ( 1a ) and anti‐(R)‐metacycloprodigiosin‐HCl ( 1b ), each with multiple conformers. Energetics and chiroptical properties, namely, electronic circular dichroism (ECD) and specific optical rotation (SOR), of (R)‐metacycloprodigiosin‐HCl have been investigated at B3LYP/6‐311++G(2d,2p) level. The experimental ECD spectra of (R)‐metacycloprodigiosin‐HCl have also been measured. Calculations indicated that the lowest energy conformer of 1b is approximately 2.7 kcal/mol lower in energy than that of 1a , and the energy barrier for anti to syn conversion is approximately 13 kcal/mol. The population weighted calculated SORs of 1a and 1b are, respectively, positive and negative. The respective calculated ECD spectra of these pseudoenantiomers show an almost mirror image relationship between them. The experimental SOR and ECD compare well with those predicted for 1b . Thus, 1b is expected to be predominant, a situation confirmed also by nuclear Overhauser effect (NOE) data, with a similar conclusion reached for prodigiosin R1. 相似文献
98.
S. Bhattacharyya S. N. Das A. B. Dey K. Nagarkar J. Lobo S. K. Kapoor H. K. Prasad 《Journal of biosciences》1997,22(1):99-109
Interferon-(IFN-γ) has been considered to be a critical protective immunomodulatory component against
Mycobacterium tuberculosis (M. tb.) infection. In this study T-cell proliferation and IFN-γ production upon stimulation with M. tb. were assessed in
patients of pulmonary tuberculosis and healthy contacts. The studies were based on lymphocyte transformation test and detection
of intracellular IFN-γ production by CD4 + ve T-cells by flowcytometry. Patients showed lower levels of proliferation, the
stimulation index being in the range of 2.17 1.1 (mean + SD) compared to the contacts (SI = 4 59±1.6) (P < 0.01). The kinetics
of intracellular induction of IFN-γ on M. tb. stimulation showed a proportional increase in the CD4 + ve T-cell population.
The increase was maximal between 96–120 h of culture. In healthy contacts the number of IFN-γ expressing CD + ve T-cells increased
to 2.5 to 41 × 104 cells/ml in M. tb. stimulated cultures compared to control cultures (0.1 – 15 × 104). In contrast patients showed no/marginal increase in CD4 + ve T-cell population expressing intracellular IFN-γ Thus the
lack of induction of IFN in CD4 + ve T-cells in patients could be a critical shortcoming in their ability to combat tubercle
bacilli infection. 相似文献
99.
The ITS sequences of Acropora spp. are the shortest so far identified in
any metazoan and are among the shortest seen in eukaryotes; ITS1 was 70-80
bases, and ITS2 was 100-112 bases. The ITS sequences were also highly
variable, but base composition and secondary structure prediction indicate
that divergent sequence variants are unlikely to be pseudogenes. The
pattern of variation was unusual in several other respects: (1) two
distinct ITS2 types were detected in both A. hyacinthus and A. cytherea,
species known to hybridize in vitro with high success rates, and a putative
intermediate ITS2 form was also detected in A. cytherea; (2) A. valida was
found to contain highly (29%) diverged ITS1 variants; and (3) A.
longicyathus contained two distinct 5.8S rDNA types. These data are
consistent with a reticulate evolutionary history for the genus Acropora.
相似文献
100.
The terminal DNA sequence requirements for piggyBac transposable element excision were explored using a plasmid-based assay in transfected, cultured insect cells. A donor plasmid containing duplicate 3′piggyBac terminal inverted repeats was constructed that allowed individual nucleotides or groups of nucleotides within one of the 3′ repeats to be mutated. The relative extent of excision using the mutated end versus the wild-type end was then assayed. Removal of even one of the terminal 3′ G nucleotides from the piggyBac inverted repeat, or removal of the dinucleotide AA from the flanking TTAA target site prevents excision of piggyBac at the mutated terminus. Incorporation of an asymmetric TTAC target site at the 3′ end does not prevent excision from the mutated end. Thus, both piggyBac DNA and flanking host DNA appear to play crucial roles in the excision process. 相似文献