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排序方式: 共有246条查询结果,搜索用时 46 毫秒
241.
M‐J Sánchez‐Calabuig C López‐Fernández E Martínez‐Nevado JF Pérez‐Gutiérrez J de la Fuente SD Johnston D Blyde K Harrison J Gosálvez 《Reproduction in domestic animals》2014,49(5):761-768
Over the last two decades, there have been significant advances in the use of assisted reproductive technology for genetic and reproductive management of captive dolphin populations, including evaluation of sperm DNA quality. This study validated a customized sperm chromatin dispersion test (SCDt) for the bottlenose dolphin (Tursiops truncatus) as a means of assessing sperm DNA damage both in the field and in the laboratory. After performing the SCDt, two different sperm morphotypes were identified: (i) sperm with fragmented DNA showed large haloes of dispersed DNA fragments emerging from a compact sperm nucleoid core and (ii) sperm containing non‐fragmented DNA displayed small compact haloes surrounded by a dense core of non‐dispersed DNA and protein complex. Estimates of sperm DNA fragmentation by means of SCDt were directly comparable to results obtained following a two‐tailed comet assay and showed a significant degree of correlation (r = 0.961; p < 0.001). This investigation also revealed that the SCDt, with minor modifications to the standard protocol, can be successfully conducted in the field using a LED florescence microscopy obtaining a high correlation (r = 0.993; p = 0.01) between the data obtained in the laboratory and in the field. 相似文献
242.
Daniel S.W. Katz Benjamin T. Connor Barrie Tiffany S. Carey 《Urban Forestry & Urban Greening》2014,13(4):756-760
Ragweed (Ambrosia artemisiifolia L.) is one of the most prolific producers of allergenic pollen in North America, and negatively impacts tens of millions of people each year. Recent work shows that local plant populations can be the most important source of allergenic pollen in the urban environment. This research emphasizes that management choices that influence species abundance can determine the burden of allergenic pollen for people living near these plant populations. In Detroit, MI, USA, ragweed populations are predominantly found in vacant lots; the management of these lots could therefore have large impacts on allergenic pollen burdens. The main form of management in these vacant lots is mowing, which occurs at frequencies ranging from monthly mowing to no mowing. We hypothesized that annual or biennial mowing would result in conditions where ragweed populations could thrive. To test this, we conducted a vegetation survey of vacant lots in Detroit, in which we quantified the mowing regime, characteristics of the vegetation, and ragweed presence and stem density. We found that ragweed was significantly more likely to be present in lots that were mowed annually or biennially; unfortunately these are the most common management types, accounting for 51% of vacant lots in Detroit. Ragweed's association with this disturbance regime fits with its early successional status, as it is most competitive in recently disturbed soils where there is reduced competition for resources such as light. We therefore recommend one of two alternative management regimes for reducing ragweed in vacant lots: either mow them frequently (multiple times a growing season) or do not mow them at all. Both approaches will reduce ragweed prevalence in vacant lots and reduce allergenic pollen exposure for people who live near vacant lots. 相似文献
243.
P. J. Baldwin H. T. L. Stewart P. R. Bird W. I. Hamer D. W. Flinn K. N. Cumming D. J. Connor 《Agroforestry Systems》1988,6(1-3):213-233
From 1983 to 1985, a network of agroforestry research trials was established at six localities throughout Victoria. This paper describes experimental designs and establishment procedures used at the trial sites. The overall aim of the research program is to provide definitive information on the costs and benefits of a wide range of agroforestry combinations. Accordingly, trials were established at the following locations to test a total of 93 tree species grown in combination with specific types of agriculture:
- Carngham (near Ballarat) — sheep grazing andPinus radiata D. Don (radiata pine);
- Hamilton (several sites) — sheep grazing and mixed tree species;
- Kyabram — irrigated pastures andEucalyptus grandis W. Hill ex Maiden (flooded gum);
- Rutherglen — cereal cropping and shelterbelts;
- Myrtleford — irrigatedMentha spp. (mint) and two clones ofPopulus spp. (poplar); and
- Neerim South (near Warragul) — cattle grazing and mixed tree species.
244.
The trails of mucus secreted by certain species of intertidal limpets serve as adhesive traps for the microalgae that are their primary food resource. In addition, the mucus trails of two solitary homing limpets, Lottia gigantea and Collisella scabra, stimulate growth of the microalgae that the limpets consume. In contrast, the trails of an aggregating limpet, Collisella digitalis, do not stimulate microalgal growth. These results and their possible ecological significance are interpreted in light of the differences in the behavioral repertoires of the three limpet species. 相似文献
245.
Caudate unit responses to nigral stimuli: evidence for a possible nigro-neostriatal pathway 总被引:2,自引:0,他引:2
J D Connor 《Science (New York, N.Y.)》1968,160(830):899-900
Electrical stimulation of the Substantia nigra evokes depressant and facilitatory responses from individually recorded caudate nucleus neurons. These effects resemble those elicited from caudate cells by microiontophoretic ejections of dopamine. Since histochemical evidence suggests that dopamine-containing fibers link the substantia nigra with the caudate, this pathway may mediate the changes in caudate spike rates produced by nigral stimuli. 相似文献
246.
Bioenergetic evaluation of diel vertical migration by bull trout (Salvelinus confluentus) in a thermally stratified reservoir
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Madeleine Eckmann Jason Dunham Edward J. Connor Carmen A. Welch 《Ecology of Freshwater Fish》2018,27(1):30-43
Many species living in deeper lentic ecosystems exhibit daily movements that cycle through the water column, generally referred to as diel vertical migration (DVM). In this study, we applied bioenergetics modelling to evaluate growth as a hypothesis to explain DVM by bull trout (Salvelinus confluentus) in a thermally stratified reservoir (Ross Lake, WA, USA) during the peak of thermal stratification in July and August. Bioenergetics model parameters were derived from observed vertical distributions of temperature, prey and bull trout. Field sampling confirmed that bull trout prey almost exclusively on recently introduced redside shiner (Richardsonius balteatus). Model predictions revealed that deeper (>25 m) DVMs commonly exhibited by bull trout during peak thermal stratification cannot be explained by maximising growth. Survival, another common explanation for DVM, may have influenced bull trout depth use, but observations suggest there may be additional drivers of DVM. We propose these deeper summertime excursions may be partly explained by an alternative hypothesis: the importance of colder water for gametogenesis. In Ross Lake, reliance of bull trout on warm water prey (redside shiner) for consumption and growth poses a potential trade‐off with the need for colder water for gametogenesis. 相似文献