Made available in DSpace on 2016-06-02T19:22:47Z (GMT). No. of bitstreams: 1 DissRBD.pdf: 921826 bytes, checksum: 40bd9588528375b232a2fdf78d110ff9 (MD5) Previous issue date: 2006-08-24 / The hypothesis of a synergy between two hormones responsible for sodium conservation, aldosterone and angiotensin II (ANG II), explains the expression of a characteristic of sodium appetite, hypertonic NaCl intake, in a hypovolemic animal. Hypertonic NaCl intake can be induced in normovolemic rats that received a combined treatment of mineralocorticoid and ANG II at individual doses not sufficient to induce sodium intake (paradigmatic synergy test). Considering the motivation to specific sodium intake another characteristic of sodium appetite, the objective of the present dissertation was to find out a role for the interaction between mineralocorticoid and ANG II on the specificity of sodium appetite. Sprague-Dawley Holtzman rats (≅ 300 g b.w.) were housed with access to water and one or more palatable (0.01 M KCl, 0.05 mM CaCl2, 0.15 M NaHCO3, 0.15 M NaCl) or hypertonic (0.50 M NaCl) mineral solutions for ingestion. In two-bottle tests, a bottle contained water and another bottle contained either 0.01 M KCl, 0.15 M NaHCO3, 0.15 M NaCl or 0.50 M NaCl. In five-bottle tests, a bottle contained water and each one of the remaining four bottles contained either 0.01 M KCl, 0.05 mM CaCl2, 0.15 M NaHCO3 or 0.15 M NaCl, respectively. In sodium depletion tests, intact rats received each a 10 mg sc. injection of furosemide or vehicle followed by 24 h access to sodium deficient food and water. Then, food was removed and mineral solutions and water were offered for recording their intake (sodium appetite test). In the paradigmatic synergy test, the animals received daily single sc injection of 2.5 mg of deoxycorticosterone acetate (DOCA) or sunflower oil (vehicle) for three days and a left lateral cerebroventricular injection of 50 ng of ANG II four hours after the last DOCA or oil injection. Fluid intake record began immediately after ANG II injection and food removal. The daily intake record showed no preference for any solution or water when animals had access to five bottles. Sodium depletion induced a preferential sodium intake, with higher NaCl than NaHCO3 intake, in either two- or five-bottle sodium appetite tests. DOCA alone enhanced the daily 0.15 M NaCl and NaHCO3 intake, but did not alter KCl or 0.50 M NaCl intake in two-bottle tests. In the paradigmatic tests with normovolemic animals, ANG II combined to oil induced the ingestion of all three palatable mineral solutions (KCl, NaHCO3, NaCl) and water, in two-bottle tests, and preference for NaHCO3 in five-bottle tests. DOCA pretreatment enhanced only sodium solution intake, particularly NaCl intake, induced by ANG II in two-bottle tests (0.15 M NaCl: DOCA/ANG II = 24.5 ± 6.7 ml/120 min. vs. OIL/ANG II = 9.2 ± 1.8 ml/120 min.; 0.15 M NaHCO3: DOCA/ANG II = 17.0 ± 1.8 ml/120 min. vs. OIL/ANG II = 14.6 ± 2.1 ml/120 min.; 0.01 M KCl: DOCA/ANG II = 9.8 ± 1.9 ml/120 min. vs. 11.9 ± 1.2 ml/120 min.), and enhanced by 80 % the total sodium solution intake in the beginning of the five-bottle test. The combined effect of DOCA with ANG II on the induction of 0.50 M NaCl intake in a two-bottle test was replicated in our animals. The results from the paradigmatic synergy test are coherent with results from sodium appetite tests, suggesting that the mineralocorticoid may turn the effect of ANG II on mineral intake more selective to sodium intake. Thus, the combined ANG II and mineralocorticoid action could contribute to the expression of two characteristics of sodium appetite, not only the acceptance of hypertonic sodium solutions, but also the selective sodium intake. / A hipótese do sinergismo entre dois hormônios responsáveis pela conservação de sódio, a aldosterona e a ANG II, explica uma característica do apetite ao sódio, a ingestão de NaCl hipertônico em um animal hipovolêmico. Ingestão de NaCl hipertônico pode ser induzida em ratos normovolêmicos que receberam um tratamento combinado de mineralocorticóide e ANG II, em doses individuais insuficientes para induzir a ingestão de sódio (teste paradigmático do sinergismo). Sendo a motivação para uma ingestão específica de sódio uma outra característica do apetite ao sódio, o objetivo desta dissertação foi o de procurar um papel para a interação entre mineralocorticóide e ANG II na especificidade do apetite ao sódio. Foram utilizados ratos Sprague-Dawley Holtzman (≅ 300 g p.c.) ambientados com livre acesso a bebedouros com água e uma ou mais soluções minerais palatáveis (KCl 0,01 M, CaCl2 0,05 mM, NaHCO3 0,15 M, NaCl 0,15 M) ou hipertônica (NaCl 0,50 M). Em testes de dois bebedouros, um dos bebedouros continha água e o outro, solução de KCl 0,01 M, NaHCO3 0,15 M, NaCl 0,15 M ou NaCl 0,50 M. Em testes de cinco bebedouros, um dos bebedouros continha água e cada um dos demais uma solução de KCl 0,01 M, CaCl2 0,05 mM, NaHCO3 0,15 M ou NaCl 0,15 M. Testes com dois ou cinco bebedouros foram empregados em animais depletados de sódio e no teste paradigmático do sinergismo. Nos testes de depleção de sódio, os animais receberam injeção sc de 10 mg de furosemida ou veículo, seguida de acesso a uma dieta hipossódica e água por vinte e quatro horas. Em seguida, o alimento foi removido e foram oferecidas soluções minerais para registro da ingestão das mesmas e de água (teste do apetite ao sódio). No teste paradigmático do sinergismo, os animais receberam injeção sc de 2,5 mg de acetato de desoxicorticosterona (DOCA) ou óleo de girassol (veículo) uma vez ao dia, durante três dias, e uma injeção de 50 ng de ANG II (ou salina) no ventrículo lateral esquerdo, quatro horas após a última injeção de DOCA ou óleo. Passou-se a registrar a ingestão de líquidos imediatamente após a injeção de ANG II e remoção da ração. O registro da ingestão diária mostrou que não houve preferência por nenhuma solução ou água durante o período de ambientação com cinco bebedouros. A depleção de sódio induziu ingestão preferencial de sódio no teste do apetite ao sódio, sendo a ingestão de NaCl 0,15 M maior do que a de NaHCO3 tanto nos testes de dois como de cinco bebedouros. O tratamento com apenas DOCA aumentou a ingestão diária de NaCl 0,15 M e de NaHCO3 sem alterar a ingestão diária de KCl e de NaCl 0,50 M, em testes de dois bebedouros. No teste paradigmático com ratos normovolêmicos, a ANG II combinada ao óleo promoveu ingestão das três soluções minerais palatáveis (KCl, NaHCO3, NaCl) e de água em testes de dupla escolha, e preferência ao NaHCO3 no teste com cinco bebedouros. O pré-tratamento com DOCA potenciou o efeito da ANG II apenas sobre a ingestão das soluções sódicas, mais evidente para NaCl, no teste com dois bebedouros (NaCl 0,15 M: DOCA/ANG II = 24,5 ± 6,7 ml/120 min. vs. ÓLEO/ANG II = 9,2 ± 1,8 ml/120 min.; NaHCO3 0,15 M: DOCA/ANG II = 17,0 ± 1,8 ml/120 min. vs. ÓLEO/ANG II = 14,6 ± 2,1 ml/120 min.; KCl 0,01 M: DOCA/ANG II = 9,8 ± 1,9 ml/120 min. vs. 11,9 ± 1,2 ml/120 min.), além de aumentar em 80 % a ingestão total de soluções sódicas no início do teste com cinco bebedouros. O efeito da indução de ingestão de NaCl 0,50 M pela combinação de DOCA com ANG II em testes de dois bebedouros foi replicado nos nossos animais. Os resultados do teste paradigmático do sinergismo são coerentes com os testes do apetite ao sódio, sugerindo que o mineralocorticóide possa tornar mais seletivo o efeito da ANG II sobre a ingestão mineral. Assim, uma interação entre ANG II e mineralocorticóide poderia contribuir para a expressão de duas características do apetite ao sódio, não apenas a aceitação de soluções hipertônicas de NaCl, mas também a ingestão seletiva de sódio.

The relations between environmental resources and biodiversity are crucial in the proper management and conservation of grasslands. Three nature reserves were chosen around the Gauteng Province, namely Roodeplaat Nature Reserve (RNR) in Tshwane, Suikerbosrand Nature Reserve (SNR) in Heidelberg, and Abe Bailey Nature Reserve (ANR) in Carletonville. We selected three sites within RNR, SNR and ANR, and paired these with adjacent sites in private farming/grazing areas adjacent to the nature reserves. At each site, species composition, species richness and plant diversity were determined with the use of 50m x 20m Modified-Whittaker plots (MWP), making a total of eighteen plots (MWP) at the nine paired sites. Two paired sites had high Shannon-Wiener Index (H’) average values at the adjacent grazing area as compared to the nature reserve area at ANR. Roodeplaat Nature Reserve (RNR) and Suikerbosrand Nature Reserve (SNR) had two paired sites with high H’ average values in the nature reserve as compared to the adjacent grazing area. The vegetation structure was similar for the three study locations, consisting of graminoids, herbs and isolated patches of shrubs. The species composition showed similarities between ANR and SNR sites, while RNR showed different species composition. SNR soils had the highest organic carbon (OC), total Carbon (C), total Nitrogen (N), Calcium (Ca), Potassium (K), Magnesium (Mg) and Sodium (Na) as compared to both ANR and RNR. Species richness had a significantly positive relationship with Organic Carbon and Total Nitrogen. Species diversity difference was detected between the nature reserves and adjacent grazing areas and the difference are likely due to a number of factors including soil properties, land disturbance and land use and management. More research is necessary to further understand the aspects impacting species richness, species diversity and species composition in grasslands. / School of Agriculture and Life Sciences / M. Sc.

Los mecanismos que contribuyen a evitar la herbivoría inducen una respuesta selectiva negativa en los herbívoros, mientras que los que contribuyen a su tolerancia inducen una respuesta selectiva positiva en los mismos. De ahí que las plantas que los poseen se clasifiquen como de baja o de alta palatabilidad, respectivamente. Los mecanismos de evitación compiten por recursos para el crecimiento, lo cual limitaría la productividad de las especies de baja palatabilidad. Por otra parte los mecanismos de evitación disminuyen la calidad de la broza (mantillo y raíces muertas), lo que limitaría la velocidad de descomposición y mineralización de las especies de baja palatabilidad. El objetivo de la presente tesis fue comparar la productividad y la velocidad de descomposición y mineralización de dos especies nativas del Caldenal, una de alta palatabilidad (Poa ligularis) y la otra de baja palatabilidad (Stipa tenuissima). Complementariamente se midió la densidad de tejido, la longevidad, la eficiencia de reabsorción de nitrógeno (N) y la eficiencia de uso de N, a nivel foliar y radical. La metodología abarcó mediciones periódicas de la biomasa aérea y subterránea por el método de la cosecha; incubaciones de hojas, raíces y suelo en condiciones in situ y/o en condiciones de laboratorio; y determinaciones del contenido de N y/o fósforo en hojas, raíces y suelo. P. ligularis fue más productiva, tanto en la parte aérea como en la parte subterránea. S. tenuissima presentó tejidos más densos a nivel foliar y radical, y más longevos y con mayor eficiencia de reabsorción y de uso de nitrógeno a nivel radical. Las hojas de P. ligularis se descompusieron y liberaron nutrientes más rápidamente que las hojas de S. tenuissima, pero las raíces de ambas especies se descompusieron y liberaron nutrientes a un ritmo similar. El concentración de N inorgánico fue similar o mayor en el suelo subyacente a P. ligularis. La tasa de mineralización in situ fue similar o mayor en el suelo subyacente a S. tenuissima, pero la tasa de mineralización potencial de nitrógeno fue superior en el suelo subyacente a P. ligularis. El N retenido en la biomasa microbiana del suelo fue similar o mayor en S. tenuissima. Si bien P. ligularis produjo broza de más calidad y en mayor cantidad que S. tenuissima, dichas diferencias no se tradujeron en forma consistente en una mayor velocidad de descomposición y de liberación de nutrientes, ni en una mayor tasa de mineralización y de concentración de nitrógeno en el suelo in situ en la primera que en la última especie. La estrechez de las diferencias en la calidad de la broza, sumado a episodios de escasez de agua recurrentes que limitarían la expresión de tales diferencias, explicaría las inconsistencias en las diferencias entre la gramínea de alta y la de baja palatabilidad en la dinámica del N mineral en el suelo subyacente a las a las mismas. / Mechanisms that help to avoid herbivory induce a negative selective response in herbivores, whereas those who contribute to herbivory tolerance induce a positive selective response in them. Plants having these mechanisms are classified as palatable or unpalatable species, respectively. Avoidance mechanisms compete for growth resources, which would limit the productivity of unpalatable species. On the other hand, the mechanisms of avoidance diminish litter quality, which would limit decomposition and mineralization speed of unpalatable species. The objective of the present thesis was to compare productivity, and decomposition and mineralization speed of two species native to the Caldenal, a palatable (Poa ligularis) and an unpalatable (Stipa tenuissima) grass species. In addition, tissue density, longevity, nitrogen (N) resorption efficiency and N use efficiency at leaf and root level were measured. The methodology included periodic measurements of above - and belowground biomass by the harvest method; in situ and/or laboratory incubations of leaves, roots and soil samples; as well as determinations of the content of N and / or phosphorus in leaves, roots and soil samples. P. ligularis was more productive, both aboveground and belowground. S. tenuissima presented more dense leaf and root tissues. The later species presented also longer tissue longevity and higher N resorption and N use efficiencies at root level. The leaves of P. ligularis decomposed and liberated nutrients faster than the leaves of S. tenuissima, but the roots of both species decomposed and liberated nutrients to a similar rate. Inorganic N content was similar or higher in the soil under P. ligularis. In situ net N mineralization was similar or higher in the soil under S. tenuissima, but potential net N mineralization was always higher in the soil under P. ligularis. N retained in the soil microbial biomass was higher in the soil under S. tenuissima. Poa ligularis produced more litter and litter of higher quality than S. tenuissima. However, these differences did not consistently translated either in faster decomposition and nutrient release rate or higher in situ net N mineralization and soil N content. Limited variation between species in the chemical composition of litter in combination to frequent moisture limitation episodes, which tend to reduce the influence of species on nutrient dynamics, may explain the inconsistencies in the differences between the palatable and the unpalatable grass in mineral N dynamic in the soil under them.

Aerial control using 1080 (sodium monofluoroacetate) baits is widely used in New Zealand for the control of introduced brushtail possums (Trichosurus vulpecula), with the aim of protecting national conservation and agricultural values from these damaging pests. This thesis integrates research, completed over 25 years, that was motivated by growing recognition in the 1970s of the extent of possum impacts and the need to improve the effectiveness and efficiency of the control operation. Field research assessed the palatability of three types of cereal-based pellet baits and carrot baits in different regions, habitat types and seasons. Palatability was assessed by the consumption of the different bait types presented independently of each other on 15-30 plots, with rotation of bait types at plots on successive nights to provide equal exposure to each bait type. There was regional variation in possums' bait preferences, possibly reflecting genotypic differences, whereas seasonal variation was less evident. Carrot bait was preferred or equally preferred to cereal bait in 14 out of 20 field trials. The proportion of possums eating baits was then investigated by, firstly, developing a technique for tracing bait acceptance using rhodamine B, a UV-fluorescent dye. In four field trials, more than 95% of possums accepted three types of dye-marked bait, eliminating bait refusal as a major reason for low kills in winter control operations. In a fifth trial, conducted in summer, only 68% of possums accepted bait suggesting that seasonal availability of favoured foods may influence bait acceptance. Since possums must encounter baits before deciding whether to eat them, field studies were undertaken to assess the coverage achieved in normal aerial baiting operations. Large gaps, up to 400 m in width, were often found between baiting swaths; these could allow some possums to survive. A controlled field experiment, using acceptance of rhodamine-dyed bait as a measure of effectiveness, showed that bait distribution was least accurate where flight paths were not marked. Where gaps of 100 m between flight paths were deliberately created, bait acceptance was slower and less than where coverage was complete. Sowing baits at 3 kg/ha was as effective as at 10 kg/ha, indicating the potential for substantially reducing operational costs by using machinery capable of faultlessly distributing baits at low rates. Navigational guidance systems were evaluated and found to improve the accuracy of bait distribution. During 1993-1997, when a lower sowing rate of 5 kg/ha was adopted operationally by regional managers, control effectiveness was unchanged but annual savings of around $9 million accrued. Because of the lack of suitable sowing machinery, a bucket was developed to permit faultless distribution of baits at lower rates, demonstrating the possibility of yet further cost-savings. The possibility of seasonal food availability affecting bait acceptance was investigated in three different forest habitats. Dyed baits were aerially distributed on 100 ha at each site in each season over two years. In each trial, fat-based condition indices of possums were calculated and the abundance of possum-preferred plant foods described. Bait acceptance was consistently high (85-100%) in the 24 trials, and was not influenced by either condition or availability of preferred foods. It seems likely that seasonal variation in operational effectiveness is caused by either the availability of sharply seasonal, scarce foods that possums may feed on intensively for brief periods, or by warmer temperatures that render 1080 less effective. The influence of 1080 on acceptance of (rhodamine-dyed) baits was investigated in a field trial. Examination of possums for dye-marking showed that 25% of possums refused to eat either a lethal quantity of bait or any bait at all, compared with 98% of possums eating non-toxic bait. This indicated that 1080 is aversive to possums, which is a potential major reason for their surviving control operations. Pen trials were therefore conducted to further examine the problem and to seek solutions. Toxic carrot baits were rejected by 27.5% of possums, equally by smell and taste aversion, whereas toxic cereal pellets were rejected by 34%, mainly by taste aversion. Orange and cinnamon were shown to be among the most preferred of 42 flavours tested and, when applied to toxic baits, 1080 was effectively masked. Bait refusal was reduced to ≤7%, the same as that recorded for possums presented with flavoured non-toxic baits. For long-term control of possum populations, aerial 1080 baiting can be used sequentially with other poisoning methods. However, the compatibility of these methods is dependent on the likelihood of possums developing bait shyness if sublethally dosed. Studies were therefore conducted to characterise and compare the four main toxicants used (1080, cyanide, cholecalciferol and brodifacoum) for induction and mitigation of bait shyness. Shyness was induced in approximately 80% of possums sublethally dosed with cyanide, 60% with 1080, 20% with cholecalciferol, and 0% with brodifacoum. Cyanide and 1080 shyness were found to persist in many possums for at least 12 and 24 months, respectively. Use of alternative bait types, and of baits containing an alternative slow-acting toxin (brodifacoum) were shown to be effective ways of overcoming shyness. This, and other related research, is reviewed to provide operational specifications that maximise the likelihood that all targeted possums will (i) encounter bait, (ii) eat it, and (iii) die. The likely future use of aerial 1080 baiting is described and the technological, economic, environmental and social constraints on its sustainability are discussed. Finally, the uptake of the research by possum managers is considered, and areas identified in the thesis where information is incomplete are summarised as prioritised topics for further research.

No description available.

Thesis(M.S.)--Auburn University, 2005. / Abstract. Vita. Includes bibliographic references.