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1.
This paper is concerned with gene survival in a population which may increase without density dependence according to a generalization of the Moran model for haploid individuals. A selective advantage to one allele and the possibility of differential reproductive rates are allowed. Simple conditions are given for ultimate homozygosity to be certain and for the possibility of ultimate polymorphism. The results complement and extend those of Heyde (1981, 1982). 相似文献
2.
Rupam Sarma 《Inorganica chimica acta》2009,362(6):1681-55
The coordination polymerization from lead(II) nitrate on reaction with 4-nitrobenzoic acid and pyridine N-oxide at room temperature passes through stepwise ligand substitution reaction. An intermediate polymer [Pb(NB)(PyO)2(NO3)]n (where NB = 4-nitrobenzoate, PyO = Pyridine N-oxide) is formed to give the final polymer [Pb(NB)2(PyO)]n. A hydrated mononuclear complex [Pb(NB)2(PyO)(H2O)] is also formed if rigorous anhydrous condition is not maintained. The reaction is extended to 4,4′-bipyridyl N-oxide (BPNO), which initially gives a coordination polymer [Pb2(NO3)(NB)3(BPNO)2]n which gets converted to another coordination polymer [Pb(NB)2(BPNO)2]n. All these complexes are structurally characterized. 相似文献
3.
In this paper the synthetic methods of three covalently linked porphyrin-phthalocyanine heteropentamers, containing four units of porphyrin linked to a central phthalocyanine (Mpor-LPc; M = 2H, Fe, L = Zn, Fe), are described. The synthetic strategy is on the basis of nucleophilic substitution reactions between [1,8,15,22-tetra nitro phthalocyanines] and [5-(4-hydroxy phenyl)-10,15,20-triphenyl porphyrins] as the phenolic alcohols. Porphyrins are linked with oxygen as spacer through meso position of phenyl group to phthalocyanines. These macromolecules were characterized by 1H NMR, UV-Vis, IR, fluorescence and mass spectroscopy. The electronic absorption spectrums of the hetero-dyad systems changed significantly upon coupling and showed a great red shift in the phthalocyanine Q-bands. These changes confirm the electron-donating effects of the porphyrin units and the extension of conjugated п-systems. The emission spectra of the products supports intramolecular energy and charge transfer between the sub-units. 相似文献
4.
1. Simple mechanical models (random walks and the 'gas model') were used to investigate the movement patterns and intergroup encounter rates of a high- and low-density subpopulation of Grey-Cheeked Mangabeys ( Cercocebus albigena johnstoni, Lydeker) at two sites in the Kibale Forest, Western Uganda.
2. Random walk simulations showed that the presence of conspecific groups could act as 'social barriers' which constrained group movements, and promoted high levels of site attachment to a specific home range area.
3. Encounter rate models showed that in the low-density subpopulation (Kanyawara), intergroup encounters occurred no more frequently than expected if groups were moving randomly and independently of each other. This was in contrast to previous analyses which suggested that Grey-Cheeked Mangabeys employed a social spacing mechanism (mediated by male loud calls) in order to reduce the frequency of encounter to below chance levels.
4. Encounters in the high-density subpopulation (Ngogo) were found to occur less frequently than expected at short range (within 100 m). This was suggested to be due to the operation of a territorial mate defence strategy by males at this site. 相似文献
2. Random walk simulations showed that the presence of conspecific groups could act as 'social barriers' which constrained group movements, and promoted high levels of site attachment to a specific home range area.
3. Encounter rate models showed that in the low-density subpopulation (Kanyawara), intergroup encounters occurred no more frequently than expected if groups were moving randomly and independently of each other. This was in contrast to previous analyses which suggested that Grey-Cheeked Mangabeys employed a social spacing mechanism (mediated by male loud calls) in order to reduce the frequency of encounter to below chance levels.
4. Encounters in the high-density subpopulation (Ngogo) were found to occur less frequently than expected at short range (within 100 m). This was suggested to be due to the operation of a territorial mate defence strategy by males at this site. 相似文献
5.
Victor F. Medina Peter M. Jeffers Steven L. Larson Waleska Perez 《International journal of phytoremediation》2000,2(4):287-295
Bleach treatment of plants was studied as a simple alternative to axenic tissue cultures for demonstrating phytodegradation of aqueous and gas-phase environmental contaminants. Parrotfeather (Myriophyllum aquaticum), spinach (Spinacia oleracea), and wheat (Triticum aestivum) were exposed to 0.525% NaC10 solutions for 15 s, then rinsed in deionized water. Plate counts indicated that 97 to 100% of viable bacteria were removed from parrotfeather and spinach. Transformation rates for 2,4,6-trinitrotoluene (TNT) by bleached and untreated parrotfeather were virtually identical. Similarly, treated and untreated spinach, wheat heads, and wheat leaves removed methyl bromide (MeBr) from air at the same rates. However, wheat root with attendant adhering soil was rendered inactive by bleach treatment. Parrotfeather roots examined by dissecting microscope and by electron microscope showed no significant damage caused by bleach treatment. 相似文献
6.
7.
T. Fatima Mitterboeck Sarah J. Adamowicz 《Proceedings. Biological sciences / The Royal Society》2013,280(1767)
The loss of flight ability has occurred thousands of times independently during insect evolution. Flight loss may be linked to higher molecular evolutionary rates because of reductions in effective population sizes (Ne) and relaxed selective constraints. Reduced dispersal ability increases population subdivision, may decrease geographical range size and increases (sub)population extinction risk, thus leading to an expected reduction in Ne. Additionally, flight loss in birds has been linked to higher molecular rates of energy-related genes, probably owing to relaxed selective constraints on energy metabolism. We tested for an association between insect flight loss and molecular rates through comparative analysis in 49 phylogenetically independent transitions spanning multiple taxa, including moths, flies, beetles, mayflies, stick insects, stoneflies, scorpionflies and caddisflies, using available nuclear and mitochondrial protein-coding DNA sequences. We estimated the rate of molecular evolution of flightless (FL) and related flight-capable lineages by ratios of non-synonymous-to-synonymous substitutions (dN/dS) and overall substitution rates (OSRs). Across multiple instances of flight loss, we show a significant pattern of higher dN/dS ratios and OSRs in FL lineages in mitochondrial but not nuclear genes. These patterns may be explained by relaxed selective constraints in FL ectotherms relating to energy metabolism, possibly in combination with reduced Ne. 相似文献
8.
B Griefahn C Künemund M Blaszkewicz K Golka P Mehnert G Degen 《Bioelectromagnetics》2001,22(8):581-588
The present study investigated the hypothesis that a strong extremely low frequency magnetic field partially suppresses the synthesis of melatonin and subsequently elevates the core body temperature. Seven healthy young men (16-22 years) took part in a control and in an exposure session. Three men experienced first the control and then the exposure session, four men experienced the sessions in reverse order. Control sessions were performed as constant routines, where the participants spent 24 hour periods continuously in bed while air temperature was 18 degrees C, illumination less than 30 lux, and the sound pressure level 50 dBA. The exposure sessions differed from that protocol only between 6 pm and 2 am when a strong extremely low frequency magnetic field was continuously applied (16.7 Hz, 0.2 mT). Assuming that the participants were unable to perceive the field consciously, they were blind against the actual condition. Salivary melatonin levels were determined hourly; body core temperatures and heart rates were registered continuously throughout. Neither of these parameters revealed alterations that can be related to the influence of the magnetic field. The present results, taken together with other investigations using that particular field, lead to the hypothesis that the effects most likely, occur, only after repetitive exposures to intermittent fields. 相似文献
9.
Populations of the vernal cladoceranDaphniopsis ephemeralis are found in woodland ponds throughout southern Ontario. The species reproduces by cyclic parthenogenesis, and genotype frequencies
at allozyme loci are ordinarily in good agreement with Hardy-Weinberg expectations. Occasional heterozygote deficiencies are
apparently the consequence of admixture of ephippial hatchlings produced in temporally separated bouts of sexual reproduction.
Considerable heterogeneity in genotypic frequencies exists among local populations in southwestern Ontario, indicating that
gene flow among populations is restricted. Inbreeding coefficients suggest that populations receive an average of 0.3 migrants
per generation. The completion of a sexual life cycle is made possible despite the brief persistence of populations by the
emergence of males from ephippial eggs and by the production of equal numbers of male and female progeny in the first parthenogenetic
brood. 相似文献
10.
The effect of Brugia pahangi infection on survival of susceptible and refractory species of the Aedes scutellaris complex 总被引:1,自引:0,他引:1
Life table statistics were used to examine the survival functions of filarial susceptible and refractory species of the Aedes scutellaris (Walker) group of mosquitoes, following infection with high and moderate doses of Brugia pahangi (Buckley & Edeson). Survivorship curves and hazard function curves were generated, and the median survival times and the proportions of mosquitoes surviving beyond the extrinsic incubation period of the parasite were determined. In the susceptible populations of Aedes polynesiensis Marks, Ae. pseudoscutellaris (Theobald) and Ae.tabu Ramalingam & Belkin a dose-response relationship was detected between parasite load and mortality. This relationship was characterized by a significant reduction in the proportions of infected female mosquitoes surviving at days 1 and 9 postinfection, reduction in the median survival times and an increase in the hazard rates as the infectious dose increased. The survival of the refractory species, Ae.alcasidi Huang and Ae.katherinensis Woodhill was not significantly affected by the infection. A positive correlation between microfilaraemia in the vertebrate host and parasite load in the susceptible mosquito populations was also observed. Regression analysis of the number of parasites recovered from susceptible mosquitoes at the time of death showed that mosquitoes at highest risk of dying harboured from 11.6 to 19.4 infective larvae when fed on a gerbil with sixty-five microfilariae per 20 microliters blood; this resulted in 34.4-40.2% mortality by day 9 postinfection. A mean number of 32.6-46.9 infective larvae was observed when these populations were exposed to a gerbil with a microfilaraemia of 150 mf/20 microliters and resulted in 72.8% to 80% mortality in these populations. Viable infective larvae were recovered from infected mosquitoes up to 50 days postinfection. 相似文献