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171.
Dynamic landscape models have generally assumed random distributions of habitat although real landscapes show spatial organization
at many scales. To explore the role of spatial structure in determining the frequency of dispersal-limited forest species,
we used a cellular landscape model divided into two zones. Zones were distributed in a random, clustered, or regular spatial
pattern. Within each zone habitat cells were randomly destroyed and regenerated, and habitat density and turnover rate were
systematically varied. A hypothetical habitat-limited species dispersed between adjacent habitat cells. All trials showed
a reduced species frequency relative to a static landscape. Reduction was greater at low habitat density (P = 0.30) than at high density (0.90) suggesting the importance of habitat connectivity in controlling species frequency. The
greatest reduction occurred when habitat was concentrated in a small, regularly distributed zone at low habitat density reflecting
the enforced isolation of individual habitat cells. Very little reduction was observed when habitat cells were packed into
a small clustered zone, a situation promoting connectivity between cells. Moderate–severe frequency reduction occurred when
habitat turnover was concentrated in a clustered zone at high habitat density, but little was observed when turnover was widely
distributed in a regular or random pattern. These results can be interpreted in terms of a source-sink function in which spatial
pattern controlled the degree of contact between landscape zones and determined opportunities for dispersal between habitat
cells. We conclude that clustering of forest habitat has the potential to maintain herb species frequency in sparsely forested
landscapes. Conversely, clustering of forest disturbance in heavily forested regions, or regular distribution of forest stands
(as often occurs in agricultural regions) creates areas which are difficult to colonize, and should be avoided. 相似文献
172.
Numerous empirical studies have examined ontogenetic trajectories in plant defenses but only a few have explored the potential
mechanisms underlying those patterns. Furthermore, most documented ontogenetic trajectories in plant defenses have generally
concentrated on aboveground tissues; thus, our knowledge regarding whole plant trends in plant defenses throughout development
or potential allocation constraints between growth and defenses is limited. Here, we document changes in plant biomass, nutritional
quality and chemical defenses for below- and aboveground tissues across seven age classes of Plantago lanceolata (Plantaginaceae) to evaluate: (1) partial and whole plant ontogenetic trajectories in constitutive chemical defenses and
nutritional quality, and (2) the role of resource allocation constraints, namely root:shoot (R:S) ratios, in explaining whole
plant investment in chemical defenses over time. Overall investment in iridoid glycosides (IGs) significantly increased, while
water and nitrogen concentrations in shoot tissues decreased with plant age. Significant variation in IG content between shoot
and root tissues across development was observed: allocation of IGs into root tissues linearly increased from younger to older
plants, while non-linear shifts in allocation of IGs during ontogeny were observed for shoot tissues. Finally, R:S ratios
only weakly explained overall allocation of resources into defenses, with young stages showing a positive relationship, while
older stages showed a negative relationship between R:S ratios and IG concentrations. Ontogenetic trajectories in plant quality
and defenses within and among plant tissues can strongly influence insect herbivores’ performance and/or predation risk; thus,
they are likely to play a significant role in mediating species interactions. 相似文献
173.
Nora Wender Jan Hegermann Bettina Brunner Brigitte Nuscher Tim Bartels Armin Giese Klaus Beyer Stefan Eimer Konstanze F Winklhofer Christian Haass 《The EMBO journal》2010,29(20):3571-3589
Aggregation of α‐synuclein (αS) is involved in the pathogenesis of Parkinson's disease (PD) and a variety of related neurodegenerative disorders. The physiological function of αS is largely unknown. We demonstrate with in vitro vesicle fusion experiments that αS has an inhibitory function on membrane fusion. Upon increased expression in cultured cells and in Caenorhabditis elegans, αS binds to mitochondria and leads to mitochondrial fragmentation. In C. elegans age‐dependent fragmentation of mitochondria is enhanced and shifted to an earlier time point upon expression of exogenous αS. In contrast, siRNA‐mediated downregulation of αS results in elongated mitochondria in cell culture. αS can act independently of mitochondrial fusion and fission proteins in shifting the dynamic morphologic equilibrium of mitochondria towards reduced fusion. Upon cellular fusion, αS prevents fusion of differently labelled mitochondrial populations. Thus, αS inhibits fusion due to its unique membrane interaction. Finally, mitochondrial fragmentation induced by expression of αS is rescued by coexpression of PINK1, parkin or DJ‐1 but not the PD‐associated mutations PINK1 G309D and parkin Δ1–79 or by DJ‐1 C106A. 相似文献
174.
Yasuro Fuse Takahiro Okamoto Kazuhide Hayakawa Hajime Karatani Etsu Yamada 《Limnology》2016,17(3):207-221
Humic substances extracted and purified from bottom sediments of northern Lake Biwa, Japan, in November 2012 and 2013 were characterized using elemental analysis, Fourier-transform infrared spectroscopy, hydrogen-1 nuclear magnetic resonance (1H NMR) analysis, and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). The infrared (IR) bands in the spectra of humic acids showed the presence of amide linkages and polysaccharides. Results of 1H NMR analysis showed that the humic acids contained approximately twice the number of aliphatic protons as those in the Japanese soil standards used for comparison. Results of the Py-GC/MS analysis, which evaluates pyrolysis temperature dependency of the amount of pyrolysis products, showed that the generation of pyrolysis products in humic acids also differed from that in Japanese soil standards but was similar to that of phytoplankton in Lake Biwa. This analysis method is the first to provide extensive information about the chemical structure of humic substances; conventional Py-GC/MS provides limited information for a single temperature. Data suggest that humic acids in lake sediments are related to chemical characteristics of phytoplankton. Results shed new light on the origins of humic substances in deep-water-lake sediments and provide insights into material recycling in such sediments. 相似文献
175.
176.
Eric Letouzé Yves Allory Marc A Bollet François Radvanyi Frédéric Guyon 《Genome biology》2010,11(7):R76
We present a computational method, TuMult, for reconstructing the sequence of copy number changes driving carcinogenesis,
based on the analysis of several tumor samples from the same patient. We demonstrate the reliability of the method with simulated
data, and describe applications to three different cancers, showing that TuMult is a valuable tool for the establishment of
clonal relationships between tumor samples and the identification of chromosome aberrations occurring at crucial steps in
cancer progression. 相似文献
177.
178.
Dinh-Toi Chu Yang Tao Le Hoang Son Duc-Hau Le 《Journal of physiology and biochemistry》2016,73(3):315-321
Recent investigations have showed that the functional thermogenic adipocytes are present in both infants and adult humans. Accumulating evidence suggests that the coexistence of classical and inducible brown (brite) adipocytes in humans at adulthood and these adipocytes function to generate heat from energy resulting in reducing body fat and improving glucose metabolism. Human thermogenic adipocytes can be differentiated in vitro from stem cells, cell lines, or adipose stromal vascular fraction. Pre-activated human brite adipocytes in vitro can maintain their thermogenic function in normal or obese immunodeficient mice; therefore, they improve glucose homeostasis and reduce fat mass in obese animals. These key findings have opened a new door to use in vitro thermogenic adipocytes as a cell therapy to prevent obesity and related disorders. Thus, this paper intends to highlight our knowledge in aspects of in vitro human brite/brown adipocytes for the further studies. 相似文献
179.
180.
During the R/V Hakuho-maru Cruise KH-95-2, Ocean Research Institute, University of Tokyo, from Tokyo, Japan to the South Pacific east of Australia (22°
N–30° S; 126° E–176° E) from June to September, 1995, 77 unidentified gonostomatid larvae (5.5–20.0 mm SL) were collected
south of 20° S with an IKMT net. They subsequently were identified as Sigmops longipinnis (Mukhacheva), and its ontogeny during the latter part of the larval stage (body form and proportions, photophores, pigmentation,
and meristics) is described here. The larvae develop a species-specific row of melanophores along the midlateral line anterior
to the caudal peduncle and another along the middorsal line from before the dorsal fin to just before the caudal fin.
Received: June 24, 2002 / Revised: November 2, 2002 / Accepted: January 31, 2003 相似文献