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The phylogenetic position of the Pedetidae, represented by a single species
Pedetes capensis, is controversial, reflecting in part the retention of
both Hystricomorphous and Sciurognathous characteristics in this rodent. In
an attempt to clarify the species evolutionary relationships, mtDNA gene
sequences from 10 rodent species (representing seven families) were
analyzed using phenetic, parsimony, and maximum-likelihood methods of
phylogenetic inference; the rabbit, Oryctolagus cuniculus (Order
Lagomorpha), and cow, Bos taurus (Order Artiodactyla), were used as
outgroups. Investigation of 714 base pairs of the protein-coding cytochrome
b gene indicate strong base bias at the third codon position with
significant rate heterogeneity evident between the three structural domains
of this gene. Similar analyses conducted on 816 base pairs of the 12S rRNA
gene revealed a transversion bias in the loop sections of all taxa. The
cytochrome b gene sequences proved useful in resolving associations between
closely related species but failed to produce consistent tree topologies at
the family level. In contrast, phylogenetic analysis of the 12S rRNA gene
resulted in strong support for the clustering of
Pedetidae/Heteromyidae/Geomyidae and Muridae in one clade to the exclusion
of the Hystricidae/Thryonomyidae and Sciuridae, a finding which is
concordant with studies of rodent fetal membranes as well as reproductive
and other anatomical features.
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To study whether absolute (m/s) or relative (body lengths/s) speed should be used to compare the vulnerability of differently sized animals, we developed a simple computer simulation. Human 'predators' were asked to 'catch' (mouse-click) prey of different sizes, moving at different speeds across a computer screen. Using the simulation, a prey's chances of escaping predation depended on its speed (faster prey were more difficult to catch than slower prey of the same body size), but also on its size (larger prey were easier to catch than smaller prey at the same speed). Catching time, the time needed to catch a prey, also depended on both prey speed and prey size. Relative prey speed (body lengths/s or body surface/s) was a better predictor of catching time than was absolute prey speed (m/s). Our experiment demonstrates that, in contrast to earlier assertions, per unit body length speed of prey may be more 'ecologically relevant' than absolute speed. Copyright 1998 The Association for the Study of Animal Behaviour. 相似文献
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Principal component models for sparse functional data 总被引:5,自引:0,他引:5
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Marleen TJ van Ampting Arjan J Schonewille Carolien Vink Robert Jan M Brummer van der Roelof Meer Ingeborg MJ Bovee-Oudenhoven 《BMC physiology》2009,9(1):6-9
Background
Glutathione, the main antioxidant of intestinal epithelial cells, is suggested to play an important role in gut barrier function and prevention of inflammation-related oxidative damage as induced by acute bacterial infection. Most studies on intestinal glutathione focus on oxidative stress reduction without considering functional disease outcome. Our aim was to determine whether depletion or maintenance of intestinal glutathione changes susceptibility of rats to Salmonella infection and associated inflammation. 相似文献37.
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Expression and Accumulation Patterns of Nitrogen-Responsive Lipoxygenase in Soybeans 总被引:3,自引:1,他引:2 下载免费PDF全文
Gene expression and protein accumulation patterns of nitrogen-responsive lipoxygenase (LOX-NR), as a representative vegetative storage protein, were investigated in nonnodulated soybeans (Glycine max [L.] Merr. cv Wye). The form of available nitrogen (supplied as NH4NO3, NH4+, NO3-, or urea) influenced the mRNA level and the amount of LOX protein, indicating that preferential accumulation of LOX may occur. Soybeans were grown with 0, 2, 5, and 16 mM total nitrogen to determine the extent to which LOX accumulation responded to soil nitrogen levels. Analysis of both mRNA and protein levels was conducted in shoot tips, stems, pod walls, and leaves over the entire life cycle of the plant. A general correlation between increasing available nitrogen level and LOX level was seen in the shoot tip and other organs throughout the soybean life cycle. However, appreciable amounts of LOX-NR mRNA and protein accumulated even when plants were grown under conditions of nitrogen deficiency. The results indicate that LOX may play an important role as a temporary storage site for amino acids in the developing shoot tip. The expression patterns of LOX-NR in plants grown under nitrogen deficiency suggest that these proteins, although responsive to nitrogen status, may not function solely as temporary storage pools for amino acids. 相似文献