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1.
T. R. Shankar Raman 《Journal of biosciences》1997,22(2):203-218
Chital or axis deer (Axis axis) form fluid groups that change in size temporally and in relation to habitat. Predictions of hypotheses relating animal density,
rainfall, habitat structure, and breeding seasonality, to changes in chital group size were assessed simultaneously using
multiple regression models of monthly data collected over a 2 yr period in Guindy National Park, in southern India. Over 2,700
detections of chital groups were made during four seasons in three habitats (forest, scrubland and grassland). In scrubland
and grassland, chital group size was positively related to animal density, which increased with rainfall. This suggests that
in these habitats, chital density increases in relation to food availability, and group sizes increase due to higher encounter
rate and fusion of groups. The density of chital in forest was inversely related to rainfall, but positively to the number
of fruiting tree species and availability of fallen litter, their forage in this habitat. There was little change in mean
group size in the forest, although chital density more than doubled during the dry season and summer. Dispersion of food items
or the closed nature of the forest may preclude formation of larger groups. At low densities, group sizes in all three habitats
were similar. Group sizes increased with chital density in scrubland and grassland, but more rapidly in the latter—leading
to a positive relationship between openness and mean group size at higher densities. It is not clear, however, that this relationship
is solely because of the influence of habitat structure. The rutting index (monthly percentage of adult males in hard antler)
was positively related to mean group size in forest and scrubland, probably reflecting the increase in group size due to solitary
males joining with females during the rut. The fission-fusion system of group formation in chital is thus interactively influenced
by several factors. Aspects that need further study, such as interannual variability, are highlighted. 相似文献
2.
3.
Adaptation to hypoxia, defined as a condition of inadequate oxygen supply, has enabled humans to successfully colonize high altitude regions. The mechanisms attempted by organisms to cope with short-term hypoxia include increased ATP production via anaerobic respiration and stabilization of Hypoxia Inducible Factor 1α (HIF-1α). However, less is known about the means through which populations adapt to chronic hypoxia during the process of development within a life time or over generations. Here we show that signaling via the highly conserved Wnt pathway impacts the ability of Drosophila melanogaster to complete its life cycle under hypoxia. We identify this pathway through analyses of genome sequencing and gene expression of a Drosophila melanogaster population adapted over >180 generations to tolerate a concentration of 3.5–4% O2 in air. We then show that genetic activation of the Wnt canonical pathway leads to increased rates of adult eclosion in low O2. Our results indicate that a previously unsuspected major developmental pathway, Wnt, plays a significant role in hypoxia tolerance. 相似文献
4.
Summary Amyloglucosidase (exo-1, 4- -D-glucosidase, EC 3.2.1.3), was coupled to glutaraldehyde activated Indion 48-R (a cross-linked macroporous anion exchanger) by Schiff base reaction. Immobilization brought about a marginal increase in the apparent Km. The bound enzyme exhibited increased stability towards urea and metal ions, but was less stable in the presence of guanidine hydrochloride. Immobilized amyloglucosidase could be stored at 4°C (in wet state) for 6–8 months without any apparent loss of activity. 相似文献
5.
We have isolated the delta-globin gene of the New-World spider monkey,
Ateles geoffroyi, and compared its nucleotide sequence with those of other
primate delta- and beta-globin genes. Among primate delta-globin genes, the
rate of nonsynonymous substitutions is much less than the rate of
synonymous substitutions. This suggests that primate delta- globin genes
may remain under evolutionary conservation, perhaps because hemoglobin A2
has an as yet unknown physiological importance.
相似文献
6.
Biochemical pathways in prokaryotes can be traced backward through evolutionary time 总被引:10,自引:0,他引:10
For the first time, a credible prokaryotic phylogenetic tree is being
assembled by Woese and others using quantitative sequence analysis of
oligonucleotides in the highly conservative rRNA. This provides an
evolutionary scale against which the evolutionary steps that led to the
arrangement and regulation of contemporary biochemical pathways can be
measured. This paper presents an emerging evolutionary picture of aromatic
amino acid biosynthesis within a large superfamily assemblage of
prokaryotes that is sufficiently developed to illustrate a new perspective
that will be applicable to many other biochemical pathways.
相似文献
7.
Uma Shankar K. S. Murali R. Uma Shaanker K. N. Ganeshaiah K. S. Bawa 《Economic botany》1996,50(3):270-279
Sustainable extraction of non-timber forest products (NTFPs) depends upon harvesting a small fraction of the total productivity. Over-exploitation can lead to a loss of biodiversity, but a low level of extraction, without value addition at the point of origin, is usually not economically feasible for extractors. Extraction and productivity levels per unit area for most non-timber forest products are unknown, nor do we have much information about value addition at various points in the marketing channels. Here we determine extraction and productivity levels for Amla trees (Phyllanthus emblica), which yield fruits that are used for a wide variety of purposes in preparation of various foods, beverages and medicines. We also present preliminary data on the price appreciation of the fruit for one of the processed products. We have determined that the current level of extraction, 60-80% of all fruits at the population level, may have a negative effect on new recruitment. We present a model for value addition that has the potential to enhance income and reduce the level of extraction. This model is currently being implemented by the Soliga community with the assistance of a non-governmental organization. 相似文献
8.
Mutational analysis of nucleoside diphosphate kinase from Pseudomonas aeruginosa: characterization of critical amino acid residues involved in exopolysaccharide alginate synthesis. 总被引:1,自引:1,他引:0
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We report the utilization of site-directed and random mutagenesis procedures in the gene encoding nucleoside diphosphate kinase (ndk) from Pseudomonas aeruginosa in order to examine the role of Ndk in the production of alginate by this organism. Cellular levels of the 16-kDa form of the Ndk enzyme are greatly reduced in P. aeruginosa 8830 with a knockout mutation in the algR2 gene (8830R2::Cm); this strain is also defective in the production of the exopolysaccharide alginate. In this study, we isolated four mutations in ndk (Ala-14-->Pro [Ala14Pro], Gly21Val, His117Gln, and Ala125Arg) which resulted in the loss of Ndk biochemical activity; hyperexpression of any of these four mutant genes did not restore alginate production to 8830R2::Cm. We identified six additional amino acid residues (Ser-43, Ala-56, Ser-69, Glu-80, Gly-91, and Asp-135) whose alteration resulted in the inability of Ndk to complement alginate production. After hyperproduction in 8830R2::Cm, it was determined that each of these six mutant Ndks was biochemically active. However, in four cases, the in vivo levels of Ndk were reduced, which consequently affected the growth of 8830R2::Cm in the presence of Tween 20. Two mutant Ndk proteins which could not complement the alginate synthesis defect in 8830R2::Cm were not affected in any characteristic examined in the present study. All of the mutant Ndks characterized which were still biochemically active formed membrane complexes with Pk, resulting in GTP synthesis. Two of the four Ndk activity mutants (His117Gln and Ala125Arg) identified were capable of being truncated to 12 kDa and formed a membrane complex with Pk; however, the complexes formed were inactive for GTP synthesis. The other two Ndk activity mutants could be truncated to 12 kDa but were not detected in membrane fractions. These results further our understanding of the role of Ndk in alginate synthesis and identify amino acid residues in Ndk which have not previously been studied as critical to this process. 相似文献
9.
Cropping on jhum fallows in north-eartern India is predominantly done for one year in a jhum cycle. If second year cropping
is done, expanse of the forest land required for slashing and burning could be reduced significantly. We tested this hypothesis
in a young (6 yr) and an old (20 yr) jhum fallow. We also evaluated if the productivity during second year cropping could
be alleviated by auxiliary measures such as tilling the soil or application of fertilizers (chemical or farm-yard manure or
both in combination). The results demonstrate that the ecosystem productivity (total dry matter production) and economic yield
(rice grain production) decline with shortening of jhum cycle. Second year cropping causes a further decline in ecosystem
productivity in old jhum field, but not in young jhum field. Economic yield from second year cropping in its traditional form
(without any fertilizer treatment) is not much lower than that in the first year, and can be improved further by manuring
the soil. Tilling of soil improves neither ecosystem productivity nor economic yield. Different fertilization treatments respond
differently; while inorganic manuring enhances ecosystem productivity, a combination of inorganic and organic manuring improves
economic yield 相似文献
10.
In Drosophila pseudoobscura, the amylase (Amy) multigene family is
contained within a series of inversions, or gene arrangements, on the third
chromosome. The Standard (ST), Santa Cruz (SC), and Tree Line (TL)
inversions are central to the phylogeny of arrangements, and have clusters
of other arrangements derived from them. The gene arrangements belonging to
each of these three clusters have a characteristic number of Amy genes,
ranging from three in ST to two in SC to one in TL. This distribution
pattern can reflect a history of either duplications or deletions, although
the data available in the past did not permit a decision between these
alternatives. We provide unambiguous evidence that three Amy genes were
present before the divergence of the ST, SC, and TL arrangements. Thus, the
current status of the Amy multigene family is the result of deletions in
the TL and SC arrangements, which created three new pseudogenes: TL
Amy2-psi, TL Amy3-psi, and SC Amy3- psi. Analysis of pseudogene sequences
revealed that, in the SC and ST arrangements, pseudogene evolution has been
retarded, most likely due to the homogenization effect of gene conversion.
Finally, by determining the original copy number, we have reconstructed the
evolutionary history of the Amy multigene family and linked it with the
evolution of the central gene arrangements.
相似文献