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81.
The relative contributions of ancestry, chance, and past and ongoing election to variation in one adaptive (larval feeding
rate) and one seemingly nonadaptive (pupation height) trait were determined in populations ofDrosophila melanogaster adapting to either low or high larval densities in the laboratory. Larval feeding rates increased rapidly in response to
high density, and the effects of ancestry, past selection and chance were ameliorated by ongoing selection within 15–20 generations.
Similarly, in populations previously kept at high larval density, and then switched to low larval density, the decline of
larval feeding rate to ancestral levels was rapid (15-20 generations) and complete, providing support for a previously stated
hypothesis regarding the costs of faster feeding inDrosophila larvae. Variation among individuals was the major contributor to variation in pupation height, a trait that would superficially
appear to be nonadaptive in the environmental context of the populations used in this study because it did not diverge between
sets of populations kept at low versus high larval density for many generations. However, the degree of divergence among populations
(FST) for pupation height was significantly less than expected for a selectively neutral trait, and we integrate results from
previous studies to suggest that the variation for pupation height among populations is constrained by stabilizing selection,
with a flat, plateau-like fitness function that, consequently, allows for substantial phenotypic variation within populations.
Our results support the view that the genetic imprints of history (ancestry and past selection) in outbreeding sexual populations
are typically likely to be transient in the face of ongoing selection and recombination. The results also illustrate the heuristic
point that different forms of selection-for example directional versus stabilizing selection—acting on a trait in different
populations may often not be due to differently shaped fitness functions, but rather due to differences in how the fitness
function maps onto the actual distribution of phenotypes in a given population. We discuss these results in the light of previous
work on reverse evolution, and the role of ancestry, chance, and past and ongoing selection in adaptive evolution. 相似文献
82.
Introgressive hybridization facilitates incorporation of genes from one species into the gene pool of another. Studies on
long-term effects of introgressive hybridization in animal systems are sparse.Drosophila nasuta (2n = 8) andD. albomicans (2n = 6)—a pair of allopatric, morphologically almost identical, cross-fertile members of thenasuta subgroup of theimmigrans species group-constitute an excellent system to analyse the impact of hybridization followed by transgressive segregation
of parental characters in the hybrid progeny. Hybrid populations ofD. nasuta andD. albomicans maintained for over 500 generations in the laboratory constitute new recombinant hybrid genomes, here termed cytoraces. The
impact of hybridization, followed by introgression and transgressive segregation, on chromosomal constitution and karyotypes,
some fitness parameters, isozymes, components of mating behaviour and mating preference reveals a complex pattern of interracial
divergence among parental species and cytoraces. This assemblage of characters in different combinations in a laboratory hybrid
zone allows us to study the emergence of new genetic systems. Here, we summarize results from our ongoing studies comparing
these hybrid cytoraces with the parental species, and discuss the implications of these findings for our understanding of
the evolution of new genetic systems.
This paper is dedicated to the memory of our teacher, Prof. N. B. Krishnamurthy. 相似文献
83.
Morton DB Hawkins P Bevan R Heath K Kirkwood J Pearce P Scott L Whelan G Webb A;British Veterinary Association Animal Welfare Foundation;Fund for Replacement of Animals in Medical Experiments;Royal Society for the Prevention of Cruelty to Animals;Universities Federation for Animal Welfare 《Laboratory animals》2003,37(4):261-299
84.
Effects of phthalic anhydride modification on horseradish peroxidase stability and activity 总被引:5,自引:0,他引:5
Phthalic anhydride (PA) modification stabilizes horseradish peroxidase (HRP) by reversal of the positive charge on two of HRP's six lysine residues. Native and PA-HRP had half-inactivation temperatures of 51 and 65 degrees C and half-lives at 65 degrees C of 4 and 17 min, respectively. PA-HRP was more resistant to dimethylformamide at room temperature and tetrahydrofuran at 60 degrees C and to unfolding by heat, guanidine chloride, EDTA, and the reducing agent tris(2-carboxyethyl)phosphine hydrochloride. Binding of the hydrophobic probe Nile Red to the native enzyme and to PA-HRP was similar. The kinetics of both HRPs with the substrates ABTS, ferrocyanide, ferulic acid, and indole-3-propionic acid were measured, as was binding of the inhibitor benzhydroxamic acid. Small improvements in the catalytic properties were detected. 相似文献
85.
Twenty Tolypothrix strains, including 15 strains of T. tenuis, three strains of T. ceylonica and one strain each of T. nodosa and T. bouteillei, were evaluated for their phycobiliprotein content and composition. Significant differences among the Tolypothrix strains were found at both inter- and intra-specific levels in the production of phycobiliprotein constituents--phycocyanin (PC), allophycocyanin (APC) and phycoerythrin (PE). Four specific parameters, viz. PC or PE content, total phycobiliprotein and total protein content, and percentage of phycobiliproteins, in a mixture of total proteins were used to select four T. tenuis and one T. ceylonica strain as useful for phycobiliproteins production. 相似文献
86.
Two plant alkaloids isolated from<Emphasis Type="Italic">Corydalis longipes</Emphasis> as potential antifungal agents 总被引:1,自引:0,他引:1
The alkaloids N-methylhydrasteine hydroxylactam and 1-methoxyberberine chloride were isolated from Corydalis longipes. Both alkaloids showed high efficacy individually (in concentration of 50-150 ppm) and also in a 1:1 mixture against spore germination of some fungi, viz. Alternaria alternata, A. brassicae, Curvularia maculans, Curvularia sp., Colletotrichum gloeosporioides, Colletotrichum sp., Helminthosporium speciferum, H. pennisetti, Helminthosporium sp., and Ustilago cynodontis. The antifungal effect of single compounds was dose-dependent. If the mutual ratio of the two components in the mixture was changed from 1:1 to a major content of any of the two compounds, the inhibitory effect on spore germination decreased. 相似文献
87.
In this article, we present some simple yet effective statistical techniques for analysing and comparing large DNA sequences.
These techniques are based on frequency distributions of DNA words in a large sequence, and have been packaged into a software
called SWORDS. Using sequences available in public domain databases housed in the Internet, we demonstrate how SWORDS can
be conveniently used by molecular biologists and geneticists to unmask biologically important features hidden in large sequences
and assess their statistical significance. 相似文献
88.
89.
Kamenarska Z Yalçin FN Ersöz T Caliş I Stefanov K Popov S 《Zeitschrift für Naturforschung. C, Journal of biosciences》2002,57(7-8):584-590
The chemical composition of the brown alga Cystoseira crinita Bory from the Eastern Mediterranean was investigated. Fourteen sterols have been identified, five of them for the first time in algae. The structure of one new sterol was established. The origin of seven sterols with short side chains was discussed. In the volatile fraction 19 compounds and in the polar fraction 15 compounds were identified. The main lipid classes were isolated and their fatty acid composition was established. 相似文献
90.
Sharmila?Anishetty Gautam?Pennathur Ramesh?AnishettyEmail author 《BMC structural biology》2002,2(1):9