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261.
Linda Nebiolo Mehmet Ozturk Bruno Brambati Susan Miller Jack Wands Aubrey Milunsky MD 《黑龙江环境通报》1990,10(9):575-581
The aim of this study was to determine the efficacy of combined maternal serum alpha-fetoprotein (MSAFP) and maternal serum human chorionic gonadotropin (MShCG) screening in detecting chromosome defects in the first trimester of pregnancy. Sera of 492 women (previously assayed for MSAFP) were analysed for MShCG under code without knowledge of cytogenetic results. Overall, 48 of 492 patients (9·8 per cent) had either an MSAFP multiple of the median ⩽0·5 or an MShCG β/a z ratio multiple of the median ⩽ 0·25, eight of whom had a fetus with a serious chromosome defect. A third of fetuses with Down' s syndrome and 83 per cent with trisomy 18 were detected at a potential‘cost’ of providing chorionic villus sampling or amniocentesis in 8·6 percent of women screened. 相似文献
262.
The mechanisms through which dominance is inherited within social groups vary from direct interactions such as fighting to
non-confrontational conventions. Liostenogaster flavolineata is a primitively eusocial hover wasp in which one female, the ‘dominant’, is the only reproductive upon the nest. The remaining
females, although capable of reproduction, behave as helpers. In this study, we investigate the rules by which helpers inherit
dominance. We removed successive dominants from 56 nests and recorded accession on un-manipulated nests. The results showed
that L. flavolineata has a strict age-based inheritance queue: new dominants are the oldest female in their groups 87% of the time. Thirteen cases
of queue-jumping were found in which young individuals were able to supplant older nestmates and inherit dominance precociously.
Queue jumpers did not differ from other wasps in terms of relatedness to other group members or body size. Individuals that
had previously worked less hard than other females of equivalent rank were significantly more likely to later jump the queue.
Queue-jumping may represent a cheating strategy or could indicate that the rule for inheriting dominance is not based purely
on relative age. We also discuss possible reasons why age-based queuing has evolved and its potential to promote the evolution
of helping behaviour. 相似文献
263.
264.
The Lower Susquehanna River Gorge and Floodplain (U.S.A.) as a Riparian Refugium for Vernal, Forest-Floor Herbs 总被引:1,自引:0,他引:1
A survey of vernal, forest-understory herbs was conducted on 52 routes, 10 sample sites each, along the Susquehanna River and its major and minor tributaries in southeastern Pennsylvania and northeastern Maryland. Mature forest stands, as compared to younger successional stands, had a greater diversity and cover of native understory herbs and greater frequencies of K -selected species such as Trillium flexipes and Dicentra canadensis . Vernal herbs with a high fidelity to the river corridor were likely to be more mesic in habitat preference, to occupy a more limited range of habitats, and to be less tolerant to disturbance than species that are also common in adjacent upland areas. The best vernal wildflower sites, which are usually in mesic or floodplain forest, may also be the most vulnerable to species loss if the canopy is removed or the forest is otherwise disturbed. Disturbance-sensitive herbs have been nearly extirpated from the Susquehanna tributaries by very intensive human development. Preservation of an appropriate matrix of microhabitats, particularly along the main river and at the mouths of the creeks, is critical to protecting the vernal flora of the region. 相似文献
265.
Population Viability Analysis of Spring Chinook Salmon in the South Umpqua River, Oregon 总被引:1,自引:0,他引:1
Run sizes of spring chinook salmon in the South Umpqua River in Oregon have declined dramatically since the early part of this century. Habitat degradation is thought to be an important factor contributing to the decline of this stock, and qualitative assessment suggests the stock is at moderate risk of extinction. We use data from this and similar stocks to develop an age-structured, density-dependent model of the population dynamics that incorporates both demographic and environmental stochasticity. Under the assumption of no further habitat destruction, the population is predicted to have a greater than 95% probability of persistence for 200 years. However, sensitivity analysis for the density-dependence estimated from historical run-return data shows that substantially lower predicted viabilities are also statistically consistent with the data. A model that simulates continued habitat degradation results in almost certain extinction within 100 years. 相似文献
266.
267.
Documenting the scale of movement among populations is an important challenge for marine ecology. Using nine microsatellite markers, evidence of genetic structure in a marine kelp, the sea palm Postelsia palmaeformis Ruprecht, was examined in the vicinity of Cape Flattery, Washington state, USA (48° 24′ N, 124°44′ W). Genetic clustering analysis implemented without reference to geographic structure strongly suggested that a number of distinct genetic clusters existed among the 245 plants sampled in August in the years 1997–2001. Subsequent analysis showed that clustering was associated with geographically defined populations both among (km scale) and within (m scale) sampling sites. F
st analysis of geographically defined populations revealed significant genetic differentiation among populations of plants as little as 5 m apart, evidence of genetic structuring at even smaller scales, and a sharp increase in F
st across populations separated by up to 23 m. F
st values were also high and approximately unchanging (F
st=0.470) for populations separated by greater distances (up to 11 km), consistent with a scenario of rare dispersal by detached, floating plants carried by variable currents. The results corroborate natural history observations suggesting that P. palmaeformis has extremely short (1–3 m) spore dispersal distances, and indicate that the dynamics of sea palm populations are more affected by local processes than recruitment from distant populations. 相似文献
268.
269.
Jacques Kagan Edgard D. Kagan Isabelle A. Kagan Peggy A. Kagan Susan Quigley 《Chemosphere》1985,14(11-12)
Anthracene, fluoranthene, and pyrene are phototoxic in
, first instar larvae of
, late embryonic forms of
, and fish (
). Since polycyclic aromatic hydrocarbons are generated in the combustion processes held responsible for the damages of acid rain, and they are introduced into the environment through other means as well, the high phototoxicity of the major pollutants, which are not carcinogenic, suggests that greater attention must be given to their environmental significance. 相似文献
270.
Open-path tunable diode laser absorption spectroscopy for acquisition of fugitive emission flux data
Thoma ED Shores RC Thompson EL Harris DB Thorneloe SA Varma RM Hashmonay RA Modrak MT Natschke DF Gamble HA 《Journal of the Air & Waste Management Association (1995)》2005,55(5):658-668
Air pollutant emission from unconfined sources is an increasingly important environmental issue. The U.S. Environmental Protection Agency (EPA) has developed a ground-based optical remote-sensing method that enables direct measurement of fugitive emission flux from large area sources. Open-path Fourier transform infrared spectroscopy (OP-FTIR) has been the primary technique for acquisition of pollutant concentration data used in this emission measurement method. For a number of environmentally important compounds, such as ammonia and methane, open-path tunable diode laser absorption spectroscopy (OP-TDLAS) is shown to be a viable alternative to Fourier transform spectroscopy for pollutant concentration measurements. Near-IR diode laser spectroscopy systems offer significant operational and cost advantages over Fourier transform instruments enabling more efficient implementation of the measurement strategy. This article reviews the EPA's fugitive emission measurement method and describes its multipath tunable diode laser instrument. Validation testing of the system is discussed. OP-TDLAS versus OP-FTIR correlation testing results for ammonia (R2 = 0.980) and methane (R2 = 0.991) are reported. Two example applications of tunable diode laser-based fugitive emission measurements are presented. 相似文献