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1.
《Journal of bryology》2013,35(1):20-21
AbstractFor obscure reasons, sporophytes of the dioicous Hamatocaulis vernicosus are currently unknown in France. With the aim of understanding this failure of sporophyte production we investigated (1) sexual phenology, (2) sex ratio pattern at different spatial scales, (3) limitation of sporophyte formation by the availability of only one sex, (4) limitation of sporophyte formation caused by the distance between male and female, (5) location of sporophytes and (6) the consevation implications of this failure of sporophyte production. Principal results show that phenology cannot explain the failure of sporophyte production. At the regional scale, sporophyte formation is prevented by the fact that several mountain ranges have single-sex populations. The production of spore capsules relies on a strict combination of factors at the local scale: occurrence of sexually expressed mixed-sex colonies, a short distance between male and female individuals and favourable environmental factors (light grazing, high water table). In the Massif Central of France spore production is unlikely because of current unfavourable conditions. Fertility patterns appeared useful in a conservation context. 相似文献
2.
The probability that protected areas will deliver their potential for maintaining or enhancing biodiversity is likely to be
maximised if they are appropriately and effectively managed. As a result, governments and conservation agencies are devoting
much attention to the management of protected areas. In the U.K., the demand for performance accountability has resulted in
Public Service Agreements (PSA) that set out targets for government departments to deliver results in return for investments
being made. One such target for England is to ensure that all nationally important wildlife sites are in favourable condition
by 2010. Here, we tested the hypothesis, of potential strategic importance, that the ecological condition of these sites is
predictable from relationships with a range of physical, environmental and demographic variables. We used binary logistic
regression to investigate these relationships, using the results of English Nature’s 1997–2003 condition assessment exercise.
Generally, sites in unfavourable condition tend to be larger in area, located at higher elevations, but with higher human
population density and are more spatially isolated from units of the same habitat. However, despite the range of different
parameters included in our models, the extent to which the condition of any given site could be predicted was low. Our results
have implications for the delivery of PSA targets, funding allocation, and the location of new protected areas. 相似文献
3.
Charles L. Nunn Peter H. Thrall Kelly Stewart Alexander H. Harcourt 《Evolutionary ecology》2008,22(4):519-543
Emerging infectious diseases threaten a wide diversity of animals, and important questions remain concerning disease emergence
in socially structured populations. We developed a spatially explicit simulation model to investigate whether—and under what
conditions—disease-related mortality can impact rates of pathogen spread in populations of polygynous groups. Specifically,
we investigated whether pathogen-mediated dispersal (PMD) can occur when females disperse after the resident male dies from
disease, thus carrying infections to new groups. We also examined the effects of incubation period and virulence, host mortality
and rates of background dispersal, and we used the model to investigate the spread of the virus responsible for Ebola hemorrhagic
fever, which currently is devastating African ape populations. Output was analyzed using regression trees, which enable exploration
of hierarchical and non-linear relationships. Analyses revealed that the incidence of disease in single-male (polygynous)
groups was significantly greater for those groups containing an average of more than six females, while the total number of
infected hosts in the population was most sensitive to the number of females per group. Thus, as expected, PMD occurs in polygynous
groups and its effects increase as harem size (the number of females) increases. Simulation output further indicated that
population-level effects of Ebola are likely to differ among multi-male–multi-female chimpanzees and polygynous gorillas,
with larger overall numbers of chimpanzees infected, but more gorilla groups becoming infected due to increased dispersal
when the resident male dies. Collectively, our results highlight the importance of social system on the spread of disease
in wild mammals. 相似文献
4.
5.
J. Sherrod DeVerse Keith A. Bailey Greg A. Foster Vaishali Mittal Stuart M. Altman Scott I. Simon Anthony G. Passerini 《Journal of visualized experiments : JoVE》2012,(65)
Atherogenesis is potentiated by metabolic abnormalities that contribute to a heightened state of systemic inflammation resulting in endothelial dysfunction. However, early functional changes in endothelium that signify an individual''s level of risk are not directly assessed clinically to help guide therapeutic strategy. Moreover, the regulation of inflammation by local hemodynamics contributes to the non-random spatial distribution of atherosclerosis, but the mechanisms are difficult to delineate in vivo. We describe a lab-on-a-chip based approach to quantitatively assay metabolic perturbation of inflammatory events in human endothelial cells (EC) and monocytes under precise flow conditions. Standard methods of soft lithography are used to microfabricate vascular mimetic microfluidic chambers (VMMC), which are bound directly to cultured EC monolayers.1 These devices have the advantage of using small volumes of reagents while providing a platform for directly imaging the inflammatory events at the membrane of EC exposed to a well-defined shear field. We have successfully applied these devices to investigate cytokine-,2 lipid-3, 4 and RAGE-induced5 inflammation in human aortic EC (HAEC). Here we document the use of the VMMC to assay monocytic cell (THP-1) rolling and arrest on HAEC monolayers that are conditioned under differential shear characteristics and activated by the inflammatory cytokine TNF-α. Studies such as these are providing mechanistic insight into atherosusceptibility under metabolic risk factors. 相似文献
6.
ABSTRACT. Mutant strain d48 and d12 cannot express serotype A. In d48, the A i-antigen gene is present in the micronucleus, but not in the macronucleus. It has recently been shown that d12 contains the A gene in its micronucleus, but its macronucleus lacks the gene. Micronuclear transplantations into enucleated cells were performed to analyze those mutants. Reciprocal transplantation between wild type and d48 confirmed that d48 contains the A gene in the micronucleus and its cytoplasm is defective. Wild type 51 enucleated cells into which were transplanted d12 micronuclei could not express A. Amiccronucleate d12 cells into which were transplanted normal micronuclei from 51 or d48 showed no expression of A. These results show that even if the micronucleus of d12 contains the A gene, it must be abnormal, and its cytoplasm is also defective the same as d48. Genetic analysis showed that heterozygote of d12 and wild type 51 or d48 caused a cure of the cytoplasmic defect of d48 and d12 during the development of macronuclei. 相似文献
7.
8.
Dimitri Karamata Harold M. Pooley Michel Monod 《Molecular & general genetics : MGG》1987,207(1):73-81
Summary A localized region of low DNA sequence homology was revealed in two strains of Bacillus subtilis by a specific 100-fold reduction in transformation by W23 DNA of the tag1 locus, a teichoic acid marker of strain 168. Fifty nine rare recombinants, hybrid at this locus, had all acquired donor-specific phage resistance characters, while losing those specific to the 168 recipient. Chemical analysis of isolated cell walls showed that these modifications are associated with major changes in the wall teichoic acids. Genetic analysis demonstrated that determinants for the ribitol phosphate polymer of strain W23 had been transferred to 168, replacing those for the glycerol phosphate polymer in the recipient. All W23 genes coding for poly(ribitol phosphate) in the hybrids and those specifying anionic wall polymers in strain 168 are clustered near hisA. In addition to tag1, the region exchanged extends just beyond gtaA in some hybrids, whereas in others it may include the more distant gtaB marker, encompassing a region sufficient to contain at least 20 average-sized genes. Surface growth, flagellation, transformability and sporulation all appeared normal in hybrids examined. Recombinants without a major wall teichoic acid from either strain were not found, suggesting that an integral transfer of genes for poly(ribitol phosphate) from W23 had occurred in all hybrids isolated. We interpret these results as indicating an essential role for anionic wall polymers in the growth of B. subtillis. 相似文献
9.
10.
P. Higgins R. J. Mathias 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1987,74(4):439-444
Summary Calli were initiated from immature embryos of nine lines of hexaploid wheat (Triticum aestivum L. em. Thell). These were the euploid lines Chinese Spring and Cappelle-Desprez, a line of Chinese Spring ditelocentric for the long arm of 4B, four substitution lines of Chinese Spring in which chromosome 4B has been replaced by its homologues from different wheat varieties and substituted into Chinese Spring and a substitution line of Besostaya I 4B into Cappelle-Desprez. The calli from these lines were found to differ in their growth rates and morphogenic and regenerative activities. The substitution of different 4B chromosomes into Chinese Spring significantly increased morphogenesis and shoot regeneration from callus. The potential for developing wheat lines with improved culture characteristics is discussed. 相似文献