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31.
Pradip Bhatnagar William Huffman Andrew King Louis Pelus William Potts et al. 《Journal of Ornithology》1994,135(1):61-71
Research Notes on Avian Biology 1994: Selected Contributions from the 21st International Ornithological CongressMorphology and Physiology: Endocrinology
Subject: Endocrinology and chronobiology 相似文献32.
EPR spectroscopy is a powerful tool to identify at a molecular level, the different steps of catalyst preparation, and of catalytic reactions: - the distribution among the different sites in zeolites can be determined; - the dispersion of the active phase may be appreciated; - the unsaturation degree of the active site may be evaluated using probe molecules such as water or13C enriched carbon monoxide.
- Deposition of paramagnetic transition metal ions onto a support is monitored, and the coordination sphere of the metallic center is characterized by EPR.
- The catalyst is also characterized after activation (thermal oxidation or reduction):
- The catalytic mechanisms can be investigated by studying the elementary steps of the catalytic reaction, as illustrated for methanol oxidation over Mo/SiO2 catalysts whose EPR results have extended the reaction mechanism proposed on the basis of kinetic data. In addition, reaction intermediates may be isolated inquasi-in situ conditions as in the case of olefin oligomerization catalyzed by Ni/SiO2 systems.
33.
Pulsed field gel electrophoresis using OFAGE, TAFE, and CHEF systems has been used to more fully characterize karyotypic variation within the two closely related fungal species of Ophiostoma ulmi sensu lato. Twelve wild-type and laboratory strains, representing the less agressive species O. ulmi and both of the biotypes of the more aggressive species O. novo-ulmi were studied and their karyotypes determined. Depending on the strain, a minimum of four to a minimum of eight chromosomal DNA bands were present that fall into three distinct size classes, with one exception. Strain CESSI6K (O. novo-ulmi, North American aggressive subgroup) contains a unique chromosomal DNA band which comigrated near a Saccharomyces cerevisiae chromosome of 0.95 Mb. This unique band was the smallest O. ulmi s. l. chromosomal DNA observed. Seven of the twelve strains shared a common chromosomal DNA banding pattern, whereas each of the other five had a unique karyotype. There was no correlation between chromosome profile and species, as some O. novo-ulmi and O. ulmi strains shared common electrophoretic karyotypes. 相似文献
34.
35.
Raven L. Bier Jennifer J. Mosher Louis A. Kaplan Jinjun Kan 《Environmental microbiology》2023,25(10):1860-1874
A mechanistic understanding of factors that structure spatiotemporal community composition is a major challenge in microbial ecology. Our study of microbial communities in the headwaters of three freshwater stream networks showed significant community changes at the small spatial scale of benthic habitats when compared to changes at mid- and large-spatial scales associated with stream order and catchment. Catchment (which included temperate and tropical catchments) had the strongest influence on community composition followed by habitat type (epipsammon or epilithon) and stream orders. Alpha diversity of benthic microbiomes resulted from interactions between catchment, habitat, and canopy. Epilithon contained relatively more Cyanobacteria and algae while Acidobacteria and Actinobacteria proportions were higher in epipsammic habitats. Turnover from replacement created ~60%–95% of beta diversity differences among habitats, stream orders, and catchments. Turnover within a habitat type generally decreased downstream indicating longitudinal linkages in stream networks while between habitat turnover also shaped benthic microbial community assembly. Our study suggests that factors influencing microbial community composition shift in dominance across spatial scales, with habitat dominating locally and catchment dominating globally. 相似文献
36.
The distribution of NO3? reduction between roots and shoots was studied in hydro-ponically-grown peach-tree seedlings (Prunus persica L.) during recovery from N starvation. Uptake, translocation and reduction of NO3?, together with transport through xylem and phloem of the newly reduced N were estimated, using 15N labellings, in intact plants supplied for 90 h with 0.5 mM NH4+ and 0.5, 1.5 or 10 mM NO3?. Xylem transport of NO3? was further investigated by xylem sap analysis in a similar experiment. The roots were the main site of NO3? reduction at all 3 levels of NO3? nutrition. However, the contribution of the shoots to the whole plant NO3? reduction increased with increasing external NO3? availability. This contribution was estimated to be 20, 23 and 42% of the total assimilation at 0.5, 1.5 and 10 mM NO3?, respectively. Both 15N results and xylem sap analysis confirmed that this trend was due to an enhancement of NO3? translocation from roots to shoots. It is proposed that the lack of NO3? export to the shoots at low NO3? uptake rate resulted from a competition between NO3? reduction in the root epidermis/cortex and NO3? diffusion to the stele. On the other hand, net xylem transport of newly reduced N was very efficient since ca 70% of the amino acids synthesized in the roots were translocated to the shoots, regardless of the level of NO3? nutrition. This net xylem transport by far exceeded the net downward phloem transport of the reduced N assimilated in shoots. As a consequence, the reduced N resulting from NO3? assimilation, principally occurring in the roots, was mainly incorporated in the shoots. 相似文献
37.
The small-subunit ribosomal DNA (rDNA) coding sequence was determined for the help Costaris Costata (Phaeophyta) and compared to those of chlorophyll a + b- and chlorophyll a + c-containing vascular and nonvascular plants. Phylogenetic comparison of all sequences indicated a common ancestor for phaeophytes, chrysophytes and oomycetes. Phylogenies based on rDNA sequence data and those based on plastid characteristics were compared. Relative evolutionary distances between some taxa, derived from rDNA sequence data, conflicted with findings of plastid-based phylogenies. 相似文献
38.
Treva Rice Angelo Tremblay Olivier Driaz Louis Prusse D.C. Rao Claude Bouchard 《Obesity (Silver Spring, Md.)》1996,4(5):441-449
A major gene hypothesis for resting metabolic rate (RMR) was investigated using segregation analysis (POINTER) of data on families participating in Phase 2 of the Québec Family Study. Complete analyses were conducted on RMR adjusted for age, and also on RMR adjusted for age and other covariates, primarily fat mass (FM) and fat-free mass (FFM). Prior to adjustment for covariates, support for a major gene hypothesis was equivocal — i.e., there was evidence for either a major gene or a multifactorial component (i.e., polygenic and/or familial environment). The multifactorial model was preferred over the major gene model, although the latter did segregate according to Mendelian expectations. However, after the effects of FM and FFM were accounted for, a major gene effect was unambiguous and compelling. The putative locus accounted for 57% of the variance, affected 7% of the sample, and led to high values of RMR. The lack of a significant multifactorial effect suggested that the familial etiology of RMR adjusted for FM and FFM was likely to be entirely a function of the major locus. Comparing the RMR results from pre- and post-adjustment for FM and FFM suggests a plausible hypothesis. We know from earlier studies in this sample that there is a putative major gene for FM and a major non-Mendelian effect for FFM. The current study leads us to speculate that: (1) the gene(s) affecting body size and body composition also may have an effect on RMR, and further (2) removal of the effect of the major gene(s) for body size and composition allowed for detection of an additional major gene affecting only the RMR. Thus, RMR appears to be an oligogenic trait. 相似文献
39.
Culturally-transmitted feeding behaviour in primates: Evidence for accelerating learning rates 总被引:1,自引:0,他引:1
Louis Lefebvre 《Primates; journal of primatology》1995,36(2):227-239
Cultural transmission implies the rapid spread of behavioural innovations when initially naïve individuals copy more informed ones. Mathematical models of transmission feature accelerating (and in most cases, logistic) rates of learning as animals that acquire an innovation provide ever increasing numbers of informers for potential learners. Conversely, non-accelerating rates have been proposed as a null hypothesis for apparent cases of cultural transmission that can best be explained by simpler mechanisms such as trial-and-error learning. Using the AIC technique for comparing models with different numbers of parameters, this paper examines the 21 cases in the primate literature where quantifiable data are available on learning rates for presumed culturally-transmitted feeding innovations. In each case, cumulative distributions over time of the frequency or proportion of individuals that acquire an innovation are compared with three accelerating functions (logistic, positive exponential, and hyperbolic sine) and two non-accelerating ones (linear and logarithmic). In 16 cases, the best fit is given by an accelerating function: nine of these support the logistic, four support the positive exponential and three, the reverse S-shaped hyperbolic sine. Individual cases often show small differences between alternative functions, but overall trends support the cultural assumption of accelerating learning rates. 相似文献
40.
Spatial and Temporal variations of mangrove fish assemblages in Martinique (French West Indies) 总被引:1,自引:1,他引:0
A study of the mangrove fish fauna in a bay of Martinique Island (French West Indies) was carried out at different seasons during two consecutive years. fishes were sampled with specific hoop-nets in the coastal areas at 8 stations.A total of 87 species was collected in the bay. Most individuals were represented by small-size specimens and juveniles. The overall species richness varied according to the stations and the sampling periods. The biomass and number of individuals were variable according to the location but remained stable in time. A factor correspondence analysis and a hierarchical clustering with median links were used to follow the evolution of the stations in space and time. Two types of stations were differentiated: the stations characterized by the mangrove and those under the influence of seagrass beds. A seasonal cycle, opposing the dry periods to the others, was observed.Thus, it seems that the use of the mangrove habitat by the fishes is optimized through a complete reorganization of communities in terms of species composition whereas the overall number and biomass remain stable. This model remains valid even for the most constraining biota of the mangrove ecosystem inhabited by a small number of well adapted species. 相似文献