7,038 research outputs found
Does diabetes mellitus play a role in restenosis and patency rates following lower extremity peripheral arterial revascularization? A critical overview
No full textPatients with diabetes mellitus (DM) are at increased risk of developing lower extremity peripheral arterial disease (PAD). The effect of DM on restenosis and patency rates in patients with PAD undergoing surgical revascularization or percutaneous interventions has not been fully clarified. We therefore critically reviewed the role of DM in restenosis, as well as primary and secondary patency rates in these patients. We searched Medline for studies investigating the effect of DM on restenosis (primary and secondary patency) rates in patients undergoing surgical/percutaneous interventions for the treatment of lower extremity PAD. Search terms used were "diabetes and peripheral arterial disease," "angioplasty," "restenosis," "revascularization," "patency rates," and "in-stent restenosis." Diabetic patients with PAD have similar restenosis, primary patency, and secondary patency rates compared with nondiabetic patients. However, mortality and amputation rates are increased in patients with DM. This increased risk of mortality and amputation may distort the estimation of restenosis and patency rates. Strict glucose control should be implemented in diabetic patients. Additionally, the use of antiplatelet agents and statins may have a beneficial effect on restenosis and patency rates. The role of radiation therapy in preventing restenosis remains to be determined. Patients with PAD and DM should receive optimal medical therapy to improve cardiovascular outcome and decrease functional decline. The direct involvement of vascular surgeons in the management of PAD patients is essential to reduce the incidence of cardiovascular events and mortality rates
Matching methods to produce maps for pest risk analysis to resources
No full textDecision support systems (DSSs) for pest risk mapping are invaluable for guiding pest risk analysts seeking to add maps to pest risk analyses (PRAs). Maps can help identify the area of potential establishment, the area at highest risk and the endangered area for alien plant pests. However, the production of detailed pest risk maps may require considerable time and resources and it is important to match the methods employed to the priority, time and detail required. In this paper, we apply PRATIQUE DSSs to Phytophthora austrocedrae, a pathogen of the Cupressaceae, Thaumetopoea pityocampa, the pine processionary moth, Drosophila suzukii, spotted wing Drosophila, and Thaumatotibia leucotreta, the false codling moth. We demonstrate that complex pest risk maps are not always a high priority and suggest that simple methods may be used to determine the geographic variation in relative risks posed by invasive alien species within an area of concern
Soil compaction effects on grassland silage yields and soil structure under different levels of compaction over three years
No full textSoil compaction has been estimated to be responsible for 33 million ha of soil degradation in Europe, reducing crop yields, however there is limited data on grassland silage yields loss. Extended grazing periods, increased size and weight of farm vehicles and more extreme weather have fostered concern over the consequences of grassland management on reduced grass yield and soil quality. This work aimed at studying the effect of increased animal trampling and mechanical (tractor) soil compaction on grassland silage mean dry matter (DM) yields and soil structure over a three year period at two UK sites. These sites were on two established perennial ryegrass fields with contrasting soil textures; an imperfectly drained silty clay loam in SW Scotland and a well drained sandy loam from central England. Results showed trampling and tractor compaction decreased mean DM yields over three years and by the third year DM yield for the trampled area was 11.4% less on the soil with greater clay content soil and 12.0% less on the more sandier soil than the no compaction control. DM yield for the tractor compaction, by the third year, was 14.5% less than no compaction DM yield, on both soil types. Compaction treatments gave the greatest reductions for the first silage cut DM yields annually, for both soil types. The largest reductions (19.0% for trampling and 37.7% for tractor) were on the soil with the greater clay content in the second year, with the coolest start to the growing season. Compaction reduced N uptake, decreased drainage and increased water filled pore spaces (WFPS). Linear regression of visual evaluation of soil structure (VESS) scores and bulk densities provided evidence that VESS is an effective tool for detecting grassland compaction and would assist with the management of moderately compacted soils where deteriorate soil conditions may result in yield loss
Psychophysical evidence for two routes to suppression before binocular summation of signals in human vision
No full textVisual mechanisms in primary visual cortex are suppressed by the superposition of gratings perpendicular to their preferred orientations. A clear picture of this process is needed to (i) inform functional architecture of image-processing models, (ii) identify the pathways available to support binocular rivalry, and (iii) generally advance our understanding of early vision. Here we use monoptic sine-wave gratings and cross-orientation masking (XOM) to reveal two cross-oriented suppressive pathways in humans, both of which occur before full binocular summation of signals. One is a within-eye (ipsiocular) pathway that is spatially broadband, immune to contrast adaptation and has a suppressive weight that tends to decrease with stimulus duration. The other pathway operates between the eyes (interocular), is spatially tuned, desensitizes with contrast adaptation and has a suppressive weight that increases with stimulus duration. When cross-oriented masks are presented to both eyes, masking is enhanced or diminished for conditions in which either ipsiocular or interocular pathways dominate masking, respectively. We propose that ipsiocular suppression precedes the influence of interocular suppression and tentatively associate the two effects with the lateral geniculate nucleus (or retina) and the visual cortex respectively. The interocular route is a good candidate for the initial pathway involved in binocular rivalry and predicts that interocular cross-orientation suppression should be found in cortical cells with predominantly ipsiocular drive
The critically endangered helmeted hornbill (Rhinoplax vigil) : threats & conservation
No full textThe Critically Endangered Helmeted Hornbill (Rhinoplax vigil) provides a case study of a species heavily threatened by human impact, primarily, the illegal wildlife trade and habitat loss. Illegal hunting has led to the number of seized individuals observed over the past 10 years being almost four times higher than the number of wild individuals observed over the past 40 years. This illegal hunting is driven by a demand for their casques to be carved and sold as ornaments illegally. Deforestation across the species’ Southeast Asian range is predicted to have reduced populations by half since 2000 in places like Borneo. These rates will likely be compounded by the 85-90% reduction of predicted species distribution under future climate change scenarios. To reduce the risk of extinction to this species, the IUCN SSC Helmeted Hornbill Working Group (HHWG) released a 10-year Conservation Strategy and Action Plan (2017-2027). This thesis explores the threats to this species and provides scientific research to meet some of the conservation Objectives under the HHWG Actions Plan.
In Part I, genetic protocols were provided for potential enforcement and conservation use. In Chapter 1 a wildlife forensic species identification protocol was created for R. vigil based on an 800-bp region of cytochrome-B DNA. A range of methods were presented to obtain DNA sufficient for sequencing and the primers validated for forensic species identification. In Chapter 2, a range of methods were tested to yield sufficient DNA from non-invasive samples of hornbills. There was no change in sequencing success for faecal samples stored up to one month in various storage media. This study highlights a range of methods for obtaining sufficient mtDNA quantity, quality, and sequences from these low-DNA-yield sample types.
In Part II, morphological and molecular methods were used to identify the sex ratio of seized casques. I then discuss potential impacts to wild individuals, where a male-skewed sex ratio of seized individuals (M116: F93) was found in Chapter 3. As R. vigil are elusive and difficult to monitor, a species distribution model was used to identify potential distribution across Borneo for monitoring and conservation purposes in Chapter 4. Distance to cropland and forest, and temperature evenness were important drivers of this species distribution. Areas of highly probable current and future distribution were highlighted, and a decline of overall distribution under future (2041-2060) climate scenarios were observed. Finally in Chapter 5, three decades of auction trade data were analysed and market trends explored to understand demand for helmeted hornbill products. They were then compared to seizure and CITES Trade data to provide a bigger picture of the trade. The data suggested that a distinct auction sub-market in illegally traded products developed during the art boom immediately following the 2008 financial crash, with volumes of traded and seized products highly correlated. This demonstrates how vulnerable an endangered species is to swings in demand.
By highlighting threats and areas for furthering the conservation of R. vigil, this thesis provides insight into processes fuelling endangered species decline, and tools to mitigate them.published_or_final_versionBiological SciencesDoctoralDoctor of Philosoph
Physiological responses and ecosystem functions of key subtidal primary producer under local and global changes
No full textOcean warming and acidification have altered the physical and chemical properties of marine environments by increasing ocean heat budget and lowering pH. Increased temperature threatens the survival of organisms by challenging their physiological limits, resulting in mortality or range shift. Reduced pH changes seawater carbon chemistry and can restructure marine communities, influencing ecosystem processes. As a result of these rapid changes, the distribution and phenology of marine producers are experiencing significant impacts - establishing baseline and mechanistic understanding behind these shifts allow for future assessment of systemic changes in ecosystems. Throughout this thesis, I examined effects of environmental conditions on the photophysiology and ecology of habitat-forming macroalgae in the genus Sargassum to provide insights on the shifts in ecosystem functions of a macroalgal-dominated ecosystem relevant to the global change setting.
Transition zones between tropical and temperate regions, such as the South China Sea, are characterized by large seasonal variability which affects algal phenology. Seasonal field surveys revealed that temperature negatively correlate with the proliferation of subtidal macroalgae in Hong Kong, especially Sargassum hemiphyllum, emulating the phenology of Sargassum forests in similar ecoregions. Biomass of this dominant species reached up to 33.8 kg m-2 in winter, contrasting the barren rocky substrates defined by encrusting algae and rock oysters during summer. Nevertheless, subtidal surveys are labour intensive and inefficient. Aerial drones equipped with high resolution cameras combined with deep learning to differentiate macroalgae from its environment are a potential replacement for field-based macroalgal surveys but are yet unproven. Therefore, I used drone surveys and deep learning (AI) combined with ground-truth sampling of biomass, to increase the sampling extent and accuracy with less labour than SCUBA surveys. Importantly, such monitoring systems may allow us to link local population productivity to regional patterns.
I then experimentally manipulated temperature and irradiance to test their effects on the productivity and growth of S. hemiphyllum. Macroalgae in the high biomass, rapid growth stage were limited by warm temperatures, however, their photosynthetic performance peaked in the same temperature range when growing in drastically different form (short and prostrate). This suggests a dimorphic adaptation to counter thermal stress may come at the expense of shortened growth season and overall lower productivity. Algal biomass will eventually enter detrital pathways mediated by microbes, which are sensitive to pH shifts. Therefore, I tested how ocean acidification changes microbial community composition and diversity and, subsequently, their degradation of algal detritus. My experiment revealed that increased microbial diversity near submarine CO2 vents and enhanced degradation rate, suggesting that restructuring of acidified microbial communities may reflect quicker carbon recycling in future oceans, ultimately limiting the sequestration capacity of macroalgal forests through biomass exportation.
As climate change alters the marine environment, physiological and ecological processes of macroalgal-dominated communities will change. However, since interactions between biotic and abiotic factors are complex, the resultant consequences may not always be straightforward. Here, I provided valuable insights on the mechanistic changes in a subtropical macroalgal-dominated biota, thus improving our understand on their functional shifts in the face of climate change.published_or_final_versionBiological SciencesDoctoralDoctor of Philosoph
Outcomes, challenges and novel enforcement solutions following the 2004 cites appendix II listing of the humphead (=napoleon) wrasse, Cheilinus undulatus (order Perciformes; family Labridae)
No full textHumphead (=Napoleon) wrasse, Cheilinus undulatus, is one of the top-priced internationally traded live reef food fish predominantly destined for consumers in Mainland China, Hong Kong and other Chinese communities. High economic incentives have driven serious overfishing of the species which, in 2004, was listed as Endangered on the IUCN Red List, and added to the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) Appendix II to avoid utilization incompatible with its survival. Hong Kong, as a signatory party of CITES and global trade hub for the species, must implement appropriate trade management and enforcement measures for its sustainable trade. This study assesses trade patterns in the species following its CITES-listing, into and through Hong Kong, evaluates enforcement effectiveness in the city, looks at outcomes for wild populations in Indonesia, the key exporter since 2010, and develops novel solutions to address implementation shortcomings detected, and enhance research capacity and education.
Trade statistics of live humphead wrasse into and through Hong Kong were compiled from government databases (1999 to 2020) and market surveys (2014 to 2020) to describe trade patterns by volume and providence. Illegal, unregulated and undocumented trade was detected in local markets where numbers surveyed exceeded legal imports over multiple years. The current inability to distinguish legal from illegally traded fish compromises effective enforcement of the CITES listing thus requiring actions to solve the problem.
Photo identification using artificial intelligence applied to the complex facial markings of humphead wrasse was explored as a potential solution to individual recognition to aid enforcement and for its research and educational potential. As proof-of-concept, tracking of unique facial markings of captive humphead wrasse revealed that patterns were unchanged for at least 2.5 years and confirmed that visually conducted comparisons could reliably distinguish among individuals over extended periods. To facilitate implementation for enforcement by the Agriculture, Fisheries and Conservation Department (AFCD), management authority of CITES in Hong Kong, encourage public participation in trade monitoring, and enhance education and research capability for the species a prototype phone application system, Saving Face, was developed.
Since 2018, ranch-sourced humphead wrasse were exported from Indonesia in addition to wild-sourced fish. The inability to distinguish wild fish from ranched fish, which are more loosely managed in the trade but exported in higher numbers, is a further challenge for enforcement. Stable isotopes were assessed to determine δ13C and δ15N diet turnover rates and differences between ranched and wild fish. While the study was inconclusive, signatures were documented and could be tested for periods longer than the 212 days of this study. Tagging is recommended to distinguish between ranched and wild fish for enforcement purposes in the absence of any other method. Loopholes in trade management by both Hong Kong and Indonesia could be addressed by adoption and/or adaptation of the tools developed. Due to the COVID-19 pandemic, the trade in the species was severely limited in 2020 and 2021 severely limiting available sample sizes/replicates and much reduced the scale of possible experiments.published_or_final_versionBiological SciencesDoctoralDoctor of Philosoph
Binocular summation of contrast remains intact in strabismic amblyopia
No full textPURPOSE. Strabismic amblyopia is typically associated with several visual deficits, including loss of contrast sensitivity in the amblyopic eye and abnormal binocular vision. Binocular summation ratios (BSRs) are usually assessed by comparing contrast sensitivity for binocular stimuli (sensBIN) with that measured in the good eye alone (sensGOOD), giving BSR = sensBIN/sensGOOD. This calculation provides an operational index of clinical binocular function, but does not assess whether neuronal mechanisms for binocular summation of contrast remain intact. This study was conducted to investigate this question.METHODS. Horizontal sine-wave gratings were used as stimuli (3 or 9 cyc/deg; 200 ms), and the conventional method of assessment (above) was compared with one in which the contrast in the amblyopic eye was adjusted (normalized) to equate monocular sensitivities.RESULTS. In nine strabismic amblyopes (mean age, 32 years), the results confirmed that the BSR was close to unity when the conventional method was used (little or no binocular advantage), but increased to approximately squareroot2 or higher when the normalization method was used. The results were similar to those for normal control subjects (n = 3; mean age, 38 years) and were consistent with the physiological summation of contrast between the eyes. When the normal observers performed the experiments with a neutral-density (ND) filter in front of one eye, their performance was similar to that of the amblyopes in both methods of assessment.CONCLUSIONS. The results indicate that strabismic amblyopes have mechanisms for binocular summation of contrast and that the amblyopic deficits of binocularity can be simulated with an ND filter. The implications of these results for best clinical practice are discussed
Population genetics and conservation biology of the endangered tree Aquilaria sinensis (Thymelaeaceae) in Hong Kong
No full textPoaching, habitat loss, and human-induced fragmentation are global issues that threaten species with extinction. Economically important species are especially susceptible. Aquilaria sinensis (Thymelaeaceae) is an evergreen tree endemic to South China that is intensively poached as a source of agarwood. Agarwood is the resinous heartwood of a small group of related trees that is highly prized in many Asian cultures for its fragrance and purported medicinal properties. As a result of agarwood’s popularity for use in a variety of products, all Aquilaria species have been heavily exploited in the wild, bringing about a drastic decrease in population sizes. Aquilaria sinensis is now assessed as Vulnerable in the IUCN global Red List. In this thesis, I use this species as an example to study the genetic legacy of a long history of anthropogenic disturbance on its conservation. This species has long been subject to rampant poaching because of rising demand for and soaring price of agarwood. Moreover, as urbanisation depletes South China’s natural areas, the countryside is subject to conversion, causing habitat loss and fragmentation, as well as poaching. In the present study, I sampled 1,464 individuals from 34 sites across the territory of Hong Kong. I genotyped the samples using 15 microsatellite markers to examine genetic diversity and population structure, test for bottlenecks and restricted gene flow, and identify priority populations for conservation. In Part One, life history traits and the demographic structure of A. sinensis in Hong Kong were examined. Genetic diversity was also compared between life history stages, as defined by size-class thresholds for onset of reproductive maturity and increased poaching risk, in order to understand whether life history traits confer tolerance to the genetic consequences of poaching. An array of life history traits associated with high fecundity and r-selection were confirmed in A. sinensis, and comparable levels of genetic diversity between life stages suggest that life history traits do grant a degree of genetic resilience. In Part Two, genetic diversity and population genetic structuring are placed in a spatial context. A pronounced genetic structure was revealed between sites on Lantau and Lamma Islands on the one hand, and in the New Territories and on Hong Kong Island on the other, with significant differences in genetic diversity indices detected between the two clusters: a lower heterozygosity and allelic richness, as well as a less diverse genetic composition, were observed among sites in the Lantau- Lamma cluster. The results imply that the two clusters have been subject to different demographic histories, genetic processes, and/or levels of anthropogenic disturbance, and thus require different conservation approaches. To inform management decision-making, Part Three sets out to identify conservation priorities among the 34 sites with respect to their heightened evolutionary distinctiveness and extirpation risk. It was revealed that different sites have varying levels of extirpation risk, and sites occupying longer branches in the Unweighted Pair Group Method with Arithmetic Mean (UPGMA) tree were consistently prioritised for conservation. This thesis presents a practical case study to bridge research output and management action.published_or_final_versionBiological SciencesDoctoralDoctor of Philosoph
Tracing atmospheric nitrogen deposition and its impact on Hong Kong and Chinese coastal ecosystem
No full textNitrogen deposition plays an important role in both air and water quality. Nitrogen emissions in cities are high mainly due to transportation and industrial activities and are predicted to further increase in the future. As nitrogen is often the limiting nutrient in coastal waters, excess nitrogen deposition may enhance phytoplankton growth, resulting in eutrophication and leading to a cascade of ecological impacts. Thus, understanding atmospheric nitrogen sources and the potential impacts of excess nitrogen deposition are crucial to mitigate nitrogen pollution in coastal waters. In this thesis, I measured stable isotopic ratios of nitrogen from wet- and dry-deposited nitrogen species in Hong Kong to identify atmospheric sources of nitrogen and their seasonal trends. These values are useful for further characterizing the source apportionment of nitrogen sources in seawater. Next, I examined the impact of nitrogen deposition on the oxygen budget within Chinese coastal waters. Specifically, I used a biogeochemical model to estimate the extent of future hypoxic areas resulting from such expected changes in nitrogen deposition in China. My results suggest that controlling nitrogen deposition can potentially reduce hypoxia. In summary, this thesis provides a new approach for studying the trends and impacts of nitrogen deposition in Hong Kong, which will shed light on the element’s present and future significance in coastal ecosystems.published_or_final_versionEarth SciencesMasterMaster of Philosoph
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