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排序方式: 共有98条查询结果,搜索用时 15 毫秒
1.
Flow alteration and thermal pollution depress modelled growth rates of an iconic riverine fish,the Murray cod Maccullochella peelii 下载免费PDF全文
Nick S. Whiterod Shaun N. Meredith Paul Humphries Bradford S. Sherman John D. Koehn Robyn J. Watts Brett A. Ingram Tom Ryan 《Ecology of Freshwater Fish》2018,27(3):686-698
The serial discontinuity concept (SDC) proposes that hypolimnetic‐releasing impoundments cause major disruptions to the naturally occurring physical, chemical and biological gradients of rivers but that this impact diminishes with distance downstream. Such a gradient in discharge, flow velocity and temperature regime occurs below a large hypolimnetic‐releasing impoundment, the Hume Dam, on the River Murray in south‐eastern Australia. To examine the effects of this disturbance gradient on a warm‐water large‐bodied freshwater fish, the Murray cod (Maccullochella peelii), a bioenergetics model was developed and calibrated to explore energy expended under differing water velocities and temperature regimes. Model simulations predicted negative growth of juveniles directly downstream of the impoundment, due largely to the energetic costs associated with active and, to a lesser extent, standard metabolism outweighing the achievable energetic gains through food consumption. As flow velocity and temperature regimes became more favourable downstream, so did the simulated growth of the species. It was not until +239 km downstream of the impoundment that the model predicted that flow velocity and temperature regimes were suitable for greater weight gains. The modelled growth responses of juvenile Murray cod are consistent with the predictions of the SDC, emphasising that changes in the bioenergetics of individuals are likely to be reflected in reduced growth rates under the changed flow velocity and temperature regimes imposed by disturbance gradients. This research represents a valuable step in the biological understanding of Murray cod within variable riverine environments and emphasises the urgency required to mitigate impacts associated with hypolimnetic impoundments. 相似文献
2.
Alencar Xavier Benjamin Hall Shaun Casteel William Muir Katy Martin Rainey 《Euphytica》2017,213(8):200
Soybean yield components and agronomic traits are connected through physiological pathways that impose tradeoffs through genetic and environmental constraints. Our primary aim is to assess the interdependence of soybean traits by using unsupervised machine learning techniques to divide phenotypic associations into environmental and genetic associations. This study was performed on large scale, jointly analyzing 14 quantitative traits in a large multi-parental population designed for genetic studies. We collected phenotypes from 2012 to 2015 from a soybean nested association panel with 40 families of approximately 140 individuals each. Pearson and Spearman correlations measured phenotypic associations. A multivariate mixed linear model provided genotypic and environmental correlations. To evaluate relationships among traits, the study used principal component and undirected graphical models from phenotypic, genotypic, and environmental correlation matrices. Results indicate that high phenotypic correlation occurs when traits display both genetic and environmental correlations. In genetic terms, length of reproductive period, node number, and canopy coverage play important roles in determining yield potential. Optimal grain yield production occurs when the growing environment favors faster canopy closure and extended reproductive length. Environmental associations found among yield components give insight into the nature of yield component compensation. The use of unsupervised learning methods provides a good framework for investigating interactions among various quantitative traits and defining target traits for breeding. 相似文献
3.
Olivier E. Decamp Clete A. Otoshi Shaun M. Moss 《Journal of the World Aquaculture Society》2006,37(4):481-489
Abstract.— Protozoans are used as bioindicators of system health in wastewater treatment plants. The objective of this study was to determine if protozoans or meiofauna could be useful bioindicators of shrimp production system health. Specifically, we noted the relative abundance of protozoans and meiofauna inhabiting a propeller-washed bead filter (PBF) used in a recirculating aquaculture system for intensive shrimp production during a 12-wk grow-out trial. Based on microscopic analysis of PBF backwash, results indicate that (1) the presence of nematodes and rotifers may reflect the age and/or organic loading of the filter; (2) feed quantity affects protozoan biomass, whereas feed quality impacts the nutritional group of protozoans that survive; (3) free-living amoeba typically are surface associated in their active feeding state and were present in most PBF samples; and (4) ciliates likely play an important ecological role in PBF used in intensive shrimp culture. 相似文献
4.
Growth of cultured mussels (Perna canaliculus Gmelin 1791) at a deep-water chlorophyll maximum layer
Shaun C Ogilvie Steve P Fox Alex H Ross Mark R James David R Schiel 《Aquaculture Research》2004,35(13):1253-1260
We tested the hypothesis that yield of the mussel Perna canaliculus (Gmelin 1791) could be increased by placing culture ropes deep into the water column to take advantage of deep‐water chlorophyll a maxima. The study site, in Pelorus Sound, New Zealand, showed periods of thermal stratification of the water column, causing a high concentration of phytoplankton in deeper water, at the thermocline. Mussels were grown simultaneously at 5 and 17 m, for up to 96 days. Mussel growth and condition index data showed no significant differences between the two depth treatments, indicating that in this system there may not be substantial mussel productivity benefits from lowering mussel farms to the deep‐water chlorophyll maximum layer. 相似文献
5.
Amanda L. Landre Shaun A. Watmough Peter J. Dillon 《Water, air, and soil pollution》2010,209(1-4):209-228
Atmospheric emissions of metals have decreased in North America; yet, metals remain an environmental concern due to their environmental persistence and toxicity to biota. In this study, pools and mass budgets were calculated for 15 metals in an acidified forested catchment in Central Ontario. Metals that were enriched in bulk deposition over background average values (As, Cd, Pb, Zn) were generally enriched in the forest floor and upper lake sediment. While the metal pool in vegetation is small compared with the soil pool, internal cycling of metals via litterfall is comparable to atmospheric deposition, soil water, and stream fluxes. Partitioning coefficients calculated from metal concentrations in soil water and bulk soil suggest that Cd, Mn, Ni, and Zn are the most mobile. The mineral soil and lake sediments were sinks for most metals, while the wetland was a source of metals during the study year, which was a drought year. Overall, lithogenic metals (Al, Ba, Co, Fe, Mn, Rb, Sr, Zn) primarily from a weathering source generally exhibited net export from the catchment, while metals contained in atmospheric pollution (As, Cd, Cr, Cu, Ni, Pb, V) exhibited net retention. Despite the acidified nature of the catchment, it functions to retain many pollutant metals. 相似文献
6.
Immobile element-based weathering estimation methods assume that Zr (or Ti) is an immobile element, and that weathering rates of other elements can be estimated according to the enrichment of Zr in weathered horizons relative to an unweathered parent material. This approach was used to estimate base cation weathering rates for 33 soil profiles on acid-sensitive terrain in north-eastern Alberta. Zirconium generally showed enrichment within the rooting zone, but the deepest (subsoil) samples were not always associated with the lowest Zr concentrations. Weathering rates estimated with the Zr depletion and Pedological Mass Balance (PMB) methods were generally low (ranges: 0-51 and 0-58 mmolc m− 2 yr− 1, respectively); however, low base cation oxide concentrations and heterogeneity within soil profiles complicated weathering rate calculations and net base cation gains were calculated for several (six) sites. Evaluation of the Zr depletion and PMB weathering estimates against those calculated with the process-oriented PROFILE model at a subset (n = 9) of the sites indicated the estimates were poorly related, with PROFILE rates typically being higher. The effects-based emissions management strategy for acid precursors in this region requires spatial coverage of soil properties (including weathering rates) across a large area, but the apparent limitations associated with the immobile element based methods in this region: identifying representative parent soils and deriving weathering rate estimates comparable to more robust methods are arguments against their candidacy for future use. 相似文献
7.
A dendrochemical survey of sugar maple (Acer saccharum Marsh) was conducted insouth-central Ontario, which encompassed twenty-two sites in areas that both exceeded orwere below the published Critical Loads with respect to acid deposition. Areas thatexceeded the Critical Load were located remote from point emission sources, but were alsocharacterized by thin, nutrient-poor soils overlying the Precambrian Shield. ThepHaq of surface soils (A-horizon) was lower at sites on the Precambrian Shield andwater-extractable concentrations of Ca decreased exponentially with decreasing soil pH. Significant polynomial relationships between soil pH and soil Ca and sugar maple growth,assessed as cumulative tree-ring growth between 1949 and 1998, explained 40% and 37% ofthe variation in sugar maple growth respectively, with lowest growth associated with lowsoil pH and low soil Ca. Furthermore, there was a significant linearrelationship between wood Ca concentrations (averaged between 1949 and 1998) and soil pHand concentrations of several trace elements in wood (Mn, Pb, Zn, Cd, Sr and Rb) were greater atlow soil pH. Poor sugar maple growth was associated with low wood Ca concentrations andhigh wood Al levels, which together accounted for 43% of the variation in sugar maplegrowth in a multiple regression model. None of the other wood chemistry variablescontributed significantly to the model. These data suggest that sugar maple grows poorlyon acidic soils with low Ca and high Al levels. Although such acidic podzols occurnaturally in some areas overlying the Precambrian Shield, if Ca losses due to aciddeposition and/or harvesting exceed inputs through weathering and deposition(i.e. exceed Critical Load), sugar maple growth may be adversely affected and ultimately lead toincreased incidence of sugar maple decline. 相似文献
8.
Eunice J. Allan Janakie P. Eeswara Shaun Johnson A. Jennifer Mordue E. David Morgan Trevor Stuchbury 《Pest management science》1994,42(3):147-152
Callus produced from leaves of a Ghanaian strain of the neem tree, Azadirachta indica A. Juss has been shown to produce the natural insecticide azadirachtin when grown in a defined medium. The azadirachtin was isolated by standard procedures of solvent partition and column chromatography monitored by supercritical fluid chromatography. Biological activity was monitored with antifeedant tests using the desert locust (Schistocerca gregaria Forsk.). The azadirachtin was identified by chromatography on three independent chromatographic systems (SFC, HPLC & TLC) and two thin-layer colour tests. It has 100% antifeedant activity at < 0.04mg litre?1. The yield of azadirachtin was 0.0007% based on dry weight of callus. 相似文献
9.
Kevin M Sales Shaun T Kingston Christopher K Atterwill Wendy M Purcell 《Pest management science》2000,56(9):825-827
The adult hen is the species of choice when assessing the potential of organophosphate compounds (OPs) to evoke OP‐induced delayed neuropathy (OPIDN). OPIDN has been shown to depend on the irreversible covalent binding of certain OPs to the enzyme neuropathy target esterase (NTE). Levels of this enzyme in human brain are similar to those in avian species. We have previously shown that the hen embryo whole brain spheroids are histotypically similar to adult brain and express measurable levels of acetylcholine esterase (AChE) and NTE, the key enzymes in mechanisms of OP toxicity. Single‐cell suspensions were prepared from meninges‐free 7 day in ovo hen brains. Cells were grown in serum‐free media and incubated on an orbital shaker at 37 °C in 5% carbon dioxide humidified air. Spheroids can be maintained long‐term in culture and allow the effects of repeated dose and recovery studies to be conducted. Hen embryo brain spheroids were exposed to varying concentrations of tri‐o‐cresyl phosphate, leptophos and its metabolite leptophos oxon at day 14 in vitro and the effects on the activity of AChE and NTE measured. Whilst current legislation regarding toxicity testing of OPs requires the use of animals, our in vitro model provides a potential pre‐screen for novel chemical entities and commercial OP mixture variants. Such an approach should refine and reduce the number of animals used in development of new materials. © 2000 Society of Chemical Industry 相似文献
10.
Differences in early developmental rate and yolk conversion efficiency in offspring of trout with alternative life histories 下载免费PDF全文
Travis E. Van Leeuwen Shaun S. Killen Neil B. Metcalfe Colin E. Adams 《Ecology of Freshwater Fish》2017,26(3):371-382
Partial migration, in which some individuals of a population migrate while other individuals remain resident, is generally associated with ontogenetic shifts to better feeding areas or as a response to environmental instability, but its underlying mechanisms remain relatively unknown. Brown trout (Salmo trutta) exhibit partial migration, with some individuals remaining in freshwater (freshwater resident) while others undertake an anadromous migration, where they spend time at sea before returning to breed in freshwater (migrant). We reared full‐sibling groups of offspring from freshwater‐resident and anadromous brown trout from the same catchment in the laboratory under common garden conditions to examine potential differences in their early development. Freshwater‐resident parents produced eggs that were slower to hatch than those of anadromous parents, but freshwater‐resident offspring were quicker to absorb their yolk and reach the stage of exogenous feeding. Their offspring also had a higher conversion efficiency from the egg stage to the start of exogenous feeding (so were larger by the start of the fry stage) than did offspring from anadromous parents despite no difference in standard metabolic rate, maximal metabolic rate or aerobic scope. Given these differences in early development, we discuss how the migration history of the parents might influence the migration probability of the offspring. 相似文献