Occurrence and extent of hybridisation between the invasive Mallard Duck and native Yellow-billed Duck in South Africa

Hybridisation between invasive and native species represents a significant threat to biodiversity. The Mallard Duck (Anas platyrhynchos) is known to hybridise with numerous closely related Anas species in regions where they have been introduced, threatening the genetic integrity of native ducks and in some instances contributing to their extinction risk. Mallard Ducks were introduced into South Africa in the 1940s and are now naturalised and widespread in the country. It has been speculated that Mallard Ducks are hybridising with native Yellow-billed Ducks (A. undulata) in South Africa, but evidence for this remains observational or purely anecdotal. Here we use data from nuclear microsatellite markers and mitochondrial DNA sequencing to show that hybridisation is indeed occuring between these two species. We found evidence for the occurance of hybridisation, mostly as crosses between Mallard Duck hens and Yellow-billed Duck drakes. Surprisingly, our results suggest that introgressive hybridisation is primarily occuring into the invasive Mallard Duck population (mostly Mallard Duck backcrosses were detected), evidenced by directionally-skewed gene flow and sex-biased mating. Whether these findings reflect true assortative mating or a case of Haldane’s rule remains unknown. We also found evidence of high connectivity between Yellow-billed Duck populations, as far as 1000 km apart, in South Africa. Taken together these results suggest that hybrid genotypes can disperse over vast distances between populations and lead to genetic pollution, even in the absence of invasive Mallard Ducks. Active management of Mallard Duck populations has been met by public resistance in some areas in South Africa, partly because of a lack of evidence showing clear impacts by these birds. This study provides some of the first scientifically-documented evidence for such impacts

Water erosion risk assessment in South Africa : towards a methodological framework

Soil erosion is a major problem confronting land and water resources in many parts of the world and the spatial extent should be assessed and continually monitored. The combination of existing erosion models and remote sensing techniques within a Geographical Information System framework is commonly utilized for erosion risk assessment. In most countries, however, especially in developing countries such as South Africa, there is still an absence of standardized methodological frameworks that deliver comparable results across large areas as a baseline for regional scale monitoring. Assessment at the regional scale is often problematic due to spatial variability of the factors controlling erosion and the lack of input and validation data. Due to limitations of scale at which techniques can be applied and processes assessed, this study implemented a multi-process and multi-scale approach to support establishment of a methodological framework for South African conditions. The approach includes assessment of (i) sheet-rill erosion at a national scale based on the principles and components defined in the (Revised) Universal Soil Loss Equation, (ii) gully erosion in a large catchment located in the Eastern Cape Province by integrating eleven important factors into a GIS, and (iii) sediment migration for a research catchment near Wartburg in KwaZulu-Natal by means of the Soil and Water Assessment Tool. Case Study i illustrates that 20% (26 million ha) of South African land is classified as having a moderate to severe actual erosion risk (emphasizing sheet-rill erosion) and describes the challenges to be overcome in assessment at this scale. Case Study ii identifies severe gully erosion affecting an area of approximately 5 273 ha in the large catchment (Tsitsa valley) of the Eastern Cape Province and highlights gully factors likely to emerge as dominant between continuous gullies and discontinuous gullies. Case Study iii illustrates that a cabbage plot in the upper reaches of a research catchment near Wartburg is a significant sediment source, but is counterbalanced by sinks (river channel and farm dams) downstream. Model assumptions affecting outputs in the context of connectivity between sources and sinks are described. The factor-based nature of this multi-process and -scale approach allowed scrutiny of the role of the main factors in contributing to erosion risk. A combination of poor vegetation cover and susceptible parent material-soil associations are confirmed as the overriding factors in South Africa, and not topography and rainfall as frequently determined in the USA and Europe. A methodological framework with three hierarchical levels is then presented for South Africa. The framework illustrates the most feasible erosion assessment techniques and input datasets for which sufficient spatial information exists, and emphasizes simplicity required for application at a regional scale with proper incorporation of the most important factors. The framework is not interpreted as a single assessment technique but rather as an approach that guides the selection of appropriate techniques and datasets according to the complexity of the erosion processes and scale dependency. It is useful in determining the relative impact of different land use and management scenarios, as well as for comparative purposes under possible future climate change scenarios.Thesis (PhD)--University of Pretoria, 2012.Geography, Geoinformatics and Meteorologyunrestricte

Soil erosion prediction under changing land use on Mauritius

More than one half of the total area of Mauritius Island (1844 km2) is under intensive cultivation, mostly sugarcane. Since the sugarcane industry is currently facing tremendous economic constraints, sugarcane cultivation may be diversified into other agricultural types such as vegetables, pineapple and forestry. Increasing concern about the sugarcane industry and the consequences of agricultural diversification, necessitated the application of soil loss prediction models within a GIS framework. Modelling of the potential soil loss in the Rivierre Des Anguilles catchment (RDAC) is undertaken to understand the extent to which soil erosion is affected by different land use types or agricultural systems. Although most of the RDAC is covered with sugarcane (62%), a wide range of landforms, micro-climates and soils exist, making the catchment representative of southern catchments in Mauritius. The study integrates GIS techniques with two empirical soil loss models: The Revised Universal Soil Loss Equation (RUSLE); and The Soil Loss Estimation Model of Southern Africa (SLEMSA). Both models, as well as the GIS application termed Soil Erosion Assessment using GIS (SEAGIS), are used to investigate average annual soil loss from the catchment under key management practices. Using data on soil erodibility, rain erosivity, topography and land cover, soil loss can be estimated under different management options for cropland (sugarcane, intercropped cane, vegetables, banana and tea) and natural vegetation (scrub and forest). RUSLE is additionally used to predict soil loss for the catchment under potential crop diversification scenarios including, vegetables, pineapple and forest. Using the empirical soil loss models in conjunction with a GIS, it is possible to compile soil erosion prediction maps of the RDAC under current and future conditions. Although soil loss in the catchment varies significantly, models show a similar trend in mean soil loss rates of the cropping systems. Rates are generally highest on steep slopes (>20%) with high rainfall (2400 mm) along the river valley and upper catchment area (above the 400 contour line). Predicted soil loss results, however, indicate a strong inverse relationship with vegetation cover. Very high soil loss values (more than 80 t.ha-1.yr-1) are attained under vegetables, moderate values (13 to 20 t.ha-1.yr-11) under intercropped cane, low (10 t.ha-1.yr-1) or very low (less than 2 t.ha-1.yr-1) under sugarcane, very low (4 t.ha-1.yr-1) to moderate (16 t.ha-1.yr-1) ratings under banana plantations, very low (less than 1 t. -1.yr-1) to high rates (41 t.ha-1.yr-1) under tea plantations, and low rates (less than 10 t.ha-1.yr-1) for natural vegetation. SLEMSA, however, predicts high erosion rates (27 t.ha-1.yr-1to 59 t.ha-1.yr-1) under natural vegetation, since the model is not developed for use in natural conditions. Crop diversification will have a considerable influence on soil erosion. RUSLE predicts a mean soil loss of 42 t.ha-1.yr-1, 20 t.ha-1.yr-1, and 0.2 t.ha-1.yr-1 under vegetables, pineapple, and forest, respectively. When compared to current conditions, the mean soil loss for the catchment will double under pineapple (increase by 100%), and quadruple under vegetables (increase by 300%). Results indicate that no appreciable erosion damage will occur in the RDAC if converted to forested land. Results provide considerable information regarding soil loss under potential land use The study also improves the understanding of factors governing erosion in Mauritius, which is important in the targeting of research and soil conservation efforts. Landowners and the government can use results to promote farming systems that do not degrade land resources.Dissertation (MSc)--University of Pretoria, 2007.Geography, Geoinformatics and MeteorologyMScUnrestricte

Prenatal evaluation of kidney function in mice using dynamic contrast-enhanced magnetic resonance imaging

Glomerular differentiation starts as soon as embryonic stage 12 in mice and suggests that kidneys may be functional at this stage. Dynamic contrast-enhanced magnetic resonance microscopy, a noninvasive imaging technique, was used to assess renal function establishment in utero. Indeed, in adults (n = 3), an intravenous injection of gadolinium-DOTA induced in a first step a massive and rapid drop in kidney signal intensity followed, in a second step, by a drop in bladder signal intensity. The delay in signal changes between kidney and bladder reflected glomerular filtration. Pregnant mice underwent anatomical and dynamic contrast-enhanced magnetic resonance microscopy on postcoital days 12-13 (n = 2), 13-14 (n = 1), 14-15 (n = 3), 15-16 (n = 2), 16-17 (n = 3), 17-18 (n = 3), and 18-19 (n = 1). Kidneys and bladder were unambiguously depicted prior to contrast agent injection on stage 15-16 embryos. Contrast agent injection allowed kidney, detection as early as stage 12-13 but not bladder. Kinetics of signal changes demonstrated that glomerular filtration is established at embryonic stage 15-16 in mice. Thus, anatomical and dynamic contrast-enhanced magnetic resonance microscopy may be a powerful noninvasive method for in vivo prenatal developmental and functional studies

Towards a transferable and cost-effective plant AFLP protocol

Amplified fragment length polymorphism (AFLP) is a powerful fingerprinting technique that is widely applied in ecological and population genetic studies. However, its routine use has been limited by high costs associated with the optimization of fluorescently labelled markers, especially for individual study systems. Here we develop a low-cost AFLP protocol that can be easily transferred between distantly related plant taxa. Three fluorescently labelled EcoRI-primers with anchors that target interspecifically conserved genomic regions were used in combination with a single non-labelled primer in our AFLP protocol. The protocol was used to genotype one gymnosperm, two monocot and three eudicot plant genera representing four invasive and four native angiosperm species (Pinus pinaster (Pinaceae), Pennisetum setaceum and Poa annua (Poaceae), Lantana camara (Verbenaceae), Bassia diffusa (Chenopodiaceae), Salvia lanceolata, Salvia africana-lutea, and Salvia africanacaerulea (Lamiaceae)). Highly polymorphic and reproducible genotypic fingerprints (between 37–144 polymorphic loci per species tested) were obtained for all taxa tested. Our single protocol was easily transferred between distantly related taxa. Measures of expected heterozygosity ranged from 0.139 to 0.196 for P. annua and from 0.168 to 0.272 for L. camara which compared well with previously published reports. In addition to ease of transferability of a single AFLP protocol, our protocol reduces costs associated with commercial kits by almost half. The use of highly conserved but abundant anchor sequences reduces the need for laborious screening for usable primers that result in polymorphic fingerprints, and appears to be the main reason for ease of transferability of our protocol between distantly related taxa

Water erosion risk assessment in South Africa : a proposed methodological framework

With the increase in human impacts on the environment, especially in terms of agricultural intensification and climate change, erosion processes need to be assessed and continually monitored. In many countries, but particularly in developing countries such as South Africa, standardized methodological frameworks that deliver comparable results across large areas as a baseline for regional scale monitoring are absent. Due to limitations of scale at which techniques can be applied and erosion processes assessed, this study describes a multi-process and multiscale approach for soil erosion risk assessment under South African conditions. The framework includes assessment of sheet-rill erosion at a national scale based on the principles and components defined in the Universal Soil Loss Equation; gully erosion in a large catchment located in the Eastern Cape Province by integrating 11 important factors into a GIS; and sediment migration for a research catchment near Wartburg in KwaZulu-Natal by means of the Soil andWater Assessment Tool. Three hierarchical levels are presented in the framework, illustrating the most feasible erosion assessment techniques and input datasets that are required for application at a regional scale with proper incorporation of the most important erosion contributing factors. The methodological framework is not interpreted as a single assessment technique but rather as an approach that guides the selection of appropriate techniques and datasets according to scale dependency and modelled complexity of the erosion processes.National Research Foundationhttp://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1468-0459hb201

Factors controlling gully development : comparing continuous and discontinuous gullies

Gully erosion is a degradation process affecting soils in many parts of theWorld. Despite the complexity of a series of collective factors across different spatial scales, previous research has not yet explicitly quantified factor dominance between different sized gullies. This factorial analysis quantifies the differences in factor dominance between continuous gullies (cgs) and discontinuous gullies (dgs). First, gullies (totaling 5273 ha) visible from SPOT 5 imagery were mapped for a catchment (nearly 5000 km2) located in the Eastern Cape Province of South Africa. Eleven important factors were integrated into a geographical information system including topographical variables, parent material-soil associations and land use–cover interactions. These were utilized in a zonal approach in order to determine the extent factors differ between cgs and dgs. Factors leading to the development of cgs are gentle footslopes in zones of saturation along drainage paths with a large contributing area, erodible duplex soils derived from mudstones and poor vegetation cover due to overgrazing. Compared to cgs conditions, more dgs occur on rolling slopes where the surface becomes less frequently saturated with a smaller contributing area, soils are more stable and shallow. Factorial analysis further illustrates that differences in factor dominance between the two groups of gullies is most apparent for soil factors. A combination of overgrazing and susceptible mudstones proves to be key factors that consistently determine the development of cgs and dgs.The ARC-ISCW, as well as Mr. D. J. Pretorius and his colleagues at the Department of Agriculture Forestry and Fisheries (DAFF), Directorate Land Use and Soil Management.http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1099-145X

Nonlinear model predictive control for improved water recovery and throughput stability for tailings reprocessing

The reprocessing of tailings aims to recover residual wealth, reclaim or rehabilitate valuable land, or mitigate safety and environmental risks. These aims all support environmental, social, and governance measures that are increasingly placed at the centre of corporate strategy. Tailings reprocessing operations are water intensive, and typically include surge tanks with both level and density averaging objectives to improve the efficiency of downstream water and mineral recovery. In this study, a rigorous dynamic model is derived to describe the rate of change of both the volume and density in these surge tanks. By simulation with industrial data it is demonstrated that the significant input disturbances typical to tailings reprocessing circuits drive a gain inversion in the density model of the surge tank. Since conventional linear averaging control approaches are not ideally suited to deal with gain inversion and multivariable control objectives a nonlinear model predictive controller (NMPC) was derived and implemented on an industrial tailings reprocessing surge tank. Results show a 5 % improvement in water recovery from the plant tailings product, and a 27 % reduction in the standard deviation of the tailings product mass flow.http://www.elsevier.com/locate/conengprachj2023Electrical, Electronic and Computer Engineerin

In vitro and in vivo evaluation of superparamagnetic iron oxide nanoparticles coated by bisphosphonates: the effects of electrical charge and molecule length.

Physicochemical coating properties are often considered to be determining factors for in vivo characteristics of superparamagnetic iron oxide nanoparticles, used as contrast agent in Magnetic Resonance Imaging (MRI). To investigate the electrical charge (modified by zero, one or two ammonium groups) and the molecule length (3, 5 or 7 methylene chains) effects of bisphosphonate-type coatings, we assessed the complement activation, in vivo plasma and tissue relaxation time alterations of intravenously injected small iron oxide nanoparticles (<25 nm) on male healthy Wistar rats. The presence of ammonium groups induces a weak activation of the complement whatever the size and the concentration of particles, whereas hydroxyethylenebisphosphonate (HEBP)-coated particles are poor complement activators only at the lowest concentration. In vivo, HEBP-coated nanoparticles have the greatest prolonged relaxation time effects, despite their higher negative electrical charge, contrary to two ammonium bearing coatings. No significant differences were observed between mono-ammonium molecular coatings