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1
Clark, Stephanie A. "Systematics, spatial analysis and conservation genetics of Meridolum corneovirens (Pfeiffer, 1851) and related forms (Gastropoda: Camaenidae) from the Sydney region of Australia". Thesis, View thesis, 2005. http://handle.uws.edu.au:8081/1959.7/640.
Testo completoAbstract (sommario):
The purpose of the present study is to examine the genetic and morphological variation found in narrow-range endemic terrestrial invertebrate species at different geographic scales, and the ramifications of this for their systematics, management and conservation. The listed endangered land snail Meridolum corneovirens and several related forms are restricted to the Sydney region, and were used to address the above issues. Morphological, anatomical, allozyme and DNA data were obtained for a total of 77 populations from across the known range of Meridolum. A particular emphasis was placed on the forms found across the Sydney region. The analysis of the different datasets, both individually and in combination indicate at least 35 taxa mostly parapatric and seven genera were represented. This includes several previously unrecognised taxa. The analysis supports the conclusion that Meridolum corneovirens belongs to a new genus. This includes several species found from eastern Sydney south along the coast to Nowra. A total of six new species and five new genera are described. The conservation and management of narrow-range endemics such as Meridolum corneovirens provide a number of challenges to conservation managers. The alternative of listing a gene pool rather than listing species separately is proposed and explore
2
Clark, S. A. (Stephanie Ann), University of Western Sydney, of Science Technology and Environment College e of Science Food and Horticulture School. "Systematics, spatial analysis and conservation genetics of Meridolum corneovirens (Pfeiffer, 1851) and related forms (Gastropoda: Camaenidae) from the Sydney region of Australia". THESIS_CSTE_SFH_Clark_S.xml, 2005. http://handle.uws.edu.au:8081/1959.7/640.
Testo completoAbstract (sommario):
The purpose of the present study is to examine the genetic and morphological variation found in narrow-range endemic terrestrial invertebrate species at different geographic scales, and the ramifications of this for their systematics, management and conservation. The listed endangered land snail Meridolum corneovirens and several related forms are restricted to the Sydney region, and were used to address the above issues. Morphological, anatomical, allozyme and DNA data were obtained for a total of 77 populations from across the known range of Meridolum. A particular emphasis was placed on the forms found across the Sydney region. The analysis of the different datasets, both individually and in combination indicate at least 35 taxa mostly parapatric and seven genera were represented. This includes several previously unrecognised taxa. The analysis supports the conclusion that Meridolum corneovirens belongs to a new genus. This includes several species found from eastern Sydney south along the coast to Nowra. A total of six new species and five new genera are described. The conservation and management of narrow-range endemics such as Meridolum corneovirens provide a number of challenges to conservation managers. The alternative of listing a gene pool rather than listing species separately is proposed and exploreDoctor of Philosophy (PhD)
3
Ho, Wai-hoong. "The taxonomy and ecology of land snails in Hong Kong, with particular reference to factors affecting their distribution and population dynamics /". Hong Kong : University of Hong Kong, 1994. http://sunzi.lib.hku.hk/hkuto/record.jsp?B20667012.
Testo completo
4
Montano-Rendon, Mauricio. "Phylogeography of littorinid snails". Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/13328/.
Testo completoAbstract (sommario):
Interactions between evolutionary forces such as natural selection, genetic drift and gene flow are complex. Natural selection can lead to parallel formation of phenotypes under similar environmental conditions. Phylogenetic relationships can be inferred from the accumulation of genetic variation caused by genetic drift, regardless of phenotypes. Gene flow between populations can sometimes facilitate the formation of species by natural selection. In this thesis, two groups of marine snails in the diverse subfamily Littorininae were studied. The three rocky-shore species Littorina saxatilis, Littorina arcana and Littorina compressa form one such group, whereas the two sister-species Littoraria cingulata and Littoraria filosa form the other group. Previous studies of the L. saxatilis complex have shown high levels of phenotypic and genetic diversity both at local and broader scales. Previous studies of L. cingulata and L. filosa have found some of the typical signatures of reinforcement. Chapters II and III focused on analysing morphological and genetic variation, respectively, within and among species in the Littorina saxatilis complex from the British Isles. Geometric morphometrics analyses revealed a diversity of shell shape among species, but especially so within L. saxatilis. Shell shape was better explained by environment rather than by geography. Molecular data obtained by high-throughput targeted capture showed the opposite pattern, i.e. genetic variation showed a strong phylogeographic pattern. Chapter IV focused on testing whether reinforcement had contributed towards speciation between Littoraria cingulata and Littoraria filosa. Approximate Bayesian computation analysis supported absence of gene flow between the species in sympatry, suggesting that reinforcement did not contribute towards speciation. However, the results need to be validated and more complex models tested. This thesis highlights the relevance of marine snails in the subfamily Littorininae as model species for addressing a wide range of evolutionary questions. It also provides a wealth of data for many potential follow-up studies.
5
Clark, Stephanie A. "Systematics, spatial analysis and conservation genetics of Meridolum corneovirens (Pfeiffer, 1851) and related forms (Gastropoda: Camaenidae) from the Sydney region of Australia /". View thesis, 2005. http://library.uws.edu.au/adt-NUWS/public/adt-NUWS20051019.154748/index.html.
Testo completo
6
Pinchuck, Shirley Clare. "The ultrastructure and histology of the defensive epidermal glands of some marine pulmonates". Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1005481.
Testo completoAbstract (sommario):
Histology and electron microscopy were used to describe and compare the structure of the dorso-lateral pedal defensive glands of three species of marine Basommatophora, Siphonaria capensis, S. serrata and S. gigas. All three species possessed multi-cellular glands that were larger and most abundant in S. capensis. In S. capensis and S. serrata, defensive glands were composed of two types (type I and II) of large secretory cells filled with product and some irregularly shaped support cells that surrounded a central lumen. The product of both cell types was produced by organelles confined to the bases of the cells. The entire gland was surrounded by a well developed layer of smooth muscle and collagen. Type I cells stained positively for neutral and sulphated mucins, and at the transmission electron microscope level the product had a reticulated appearance. By contrast type II gland cells stained very positively for acidic mucins and the secretory product was formed as large granular vesicles. The product from both types of cell, which appeared to be secreted by holocrine secretion, mixed in the lumen of the duct. Individuals of Siphonaria gigas had two types of lateral pedal glands, a large multi-cellular type and a tubular unicellular gland. The multi-cellular glands, which were surrounded by poorly developed muscle, contained one type of gland cell that stained for neutral and sulphated mucins only, as well as some support cells. The tubular glands contained a heterogeneous product that stained very positively for neutral and sulphated mucins. In addition two species of shell-less marine Systellommatophorans, Onchidella capensis and O. hildae, were examined. Onchidellids also posses large marginal, multi-cellular, epidermal glands that produce a repugnatorial secretion. Like the multi-cellular epidermal glands of siphonariids, those of onchidellids are surrounded by layers of smooth muscle. The muscular capsule was particularly well developed in both species of onchidellid, but more so in O. hildae. In addition, this study has shown that unlike siphonariids, muscle fibres run between the gland cells of O. capensis and O. hildae. Unlike siphonariids, onchidellids have a layer of epithelial cells lining the lumen of the gland. The well developed muscle layer and the strands of muscle running between the different gland cells indicates that the glands can be constricted to forcibly propel their secretions along the length of the duct and away from the body of the animal. Based on their product, glands of O. capensis were comprised of five different types of secretory cell and O. hildae only four. Histological and histochemical staining of the glands of showed that the secretory product is largely made up of acidic mucopolysaccharides and neutral and sulphated mucins. A single species from the order Eupulmonata, Trimusculus costatus, was examined and the glands were very different to the species from the siphonariids and onchidellids. Trimusculus costatus does not have large multi-cellular glands encapsulated in a well developed muscle layer, but based on their cell contents, three different types of large unicellular gland cell can be recognised. The glands of T. costatus gave positive results for acid, neutral and sulphated mucins, but negative results for carboxylated mucin. It is possible that the mucous secreted by T. costatus is also an anti-bacterial agent and whilst not totally eliminating bacteria may prevent the accumulation of epibionts on these sedentary limpets. The acidic or sulphated nature of the secretions may help in this role. The defensive mucous secretions of Siphonaria and Onchidella contain polypropionate derivatives, whilst the active ingredients of Trimusculus mucus have been identified as labdane diterpenes, similar to those produced by opisthobranchs. The structure of the glands thought to produce these repungnatorial secretions is very different, with the glands of T. costatus resembling those of the opisthobranchs.
7
Fearon, Janine Lee. "The genetic diversity and conservation biology of the rare terrestrial snail genus Prestonella". Thesis, Rhodes University, 2011. http://hdl.handle.net/10962/d1003760.
Testo completoAbstract (sommario):
Prestonella bowkeri and Prestonella nuptialis are montane specialists endemic to the southern Great Escarpment of South Africa. Phylogeographic analyses of these species based on mitochondrial markers CO1 and 16S reveal extremely high levels of divergence between populations indicating a lack of gene flow between populations. This is not surprising, because P. nuptialis and P. bowkeri have limited dispersal capacity, low vagility, a highly fragmented distribution and are habitat specialists that are restricted to isolated mesic refugia associated with waterfalls and montane seepages. A relaxed Bayesian clock estimate suggests that populations diverged from one another during the mid-late Miocene (12.5-7 MYA) which coincides with the modern trends of seasonal aridity which began during the Miocene. This result should be viewed with caution because the rates used are at best imprecise estimates of mutation rates in snails. There is no clear dichotomy between the two species and P. bowkeri is paraphyletic with respect to P. nuptialis, as a consequence the taxonomy is unclear. Due to the high levels of sequence divergence between populations they may be considered as evolutionary significant units (ESU’s). An assessment of haplotype diversity (h) and nucleotide diversity (π) reveals that populations in the western part of the Great Escarpment are more genetically depauperate than populations in the east. Correlations between genetic diversity and climatic variables show that genetically depauperate populations are found in areas that have lower annual rainfall, less reliable rainfall and higher potential evaporation, all factors associated with a drier, less mesic environment that increases the chances of a population bottleneck. This indicates that a shift towards a more arid environment may be a driver of genetic erosion. Historical climate change may thus have affected the amount and distribution of genetic diversity across the Great Escarpment since the Miocene. This has serious future implications for the survival of Prestonella. With predicted increase in global temperatures, climate change in South Africa is likely to result in range contraction and an eastward range shift for many species in the drier central and western areas (Erasmus et al. 2002) and regions along the Great Escarpment are likely to become more arid. Prestonella populations found living on inselbergs along the Great Escarpment are already restricted to site specific watercourses and seepages. An increase in the periods between stream flow, and increasing rainfall variability and mean annual potential evaporation are likely to have an adverse affect on species living in these habitats, resulting in further bottlenecks and possibly local extinction. An IUCN assessment of P. nuptialis and P. bowkeri suggests that these two species are probably endangered. The issue surrounding the conservation of Prestonella species is that they are threatened by global climate change, which cannot be simply restricted or prevented, which makes dealing with the threat of climate change difficult. Assisted migration (MA) may be considered as a method to prevent possible future extinctions of Prestonella populations, but will only be considered as a last resort. The thermal tolerance (Arrhenius breaking temperature and flat-line temperature) of individual snails from three Prestonella populations (one forest population and two thicket populations) were assessed using infrared sensors that detected changes in heart rate with increasing temperature. The forest population had a significantly lower Arrhenius breaking temperature (ABT) and flat-line temperature (FLT) than the two thicket population (p<0.05). Our results do not show a correlation between upper thermal limits and maximum habitat temperatures or other climatic variables in Prestonella populations. Although no correlation is found between ABT and maximum habitat temperature, it is likely that the differences seen between these populations are due to local micro-climate adaptation. The climatic variables used in this experiment are coarse estimates from GIS data and do not reflect actual microhabitat conditions. Forest environments are less heat stressed than thicket environments due to the forest canopy which may explain the lower ABT and FLT of the forest population.
8
Rupp, Jens C. "Mate choice and parasitism in freshwater snails". Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339354.
Testo completo
9
Shigemiya, Yusuke. "Evolution of colour polymorphism in neritid snails". Kyoto University, 2004. http://hdl.handle.net/2433/147702.
Testo completoAbstract (sommario):
Kyoto University (京都大学)0048
新制・課程博士
博士(人間・環境学)
甲第10943号
人博第230号
15||185(吉田南総合図書館)
新制||人||58(附属図書館)
UT51-2004-G790
京都大学大学院人間・環境学研究科環境相関研究専攻
(主査)教授 加藤 真, 教授 松井 正文, 助教授 宮下 英明
学位規則第4条第1項該当
10
Tang, Simon. "Studies on molluscicidal compounds from Phytolacca dodecandra ('Endod') and Millettia thonningii". Thesis, King's College London (University of London), 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284415.
Testo completo
11
Pedder, Sibella Margaretha. "The actions of neuroactive peptides on identified central neurons of Helix aspersa". Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302340.
Testo completo
12
Cadogan, Anna-Karina. "Characterization of 5-hydroxytryptamine receptors in the snail, Helix aspersa". Thesis, University of St Andrews, 1992. http://hdl.handle.net/10023/14627.
Testo completoAbstract (sommario):
The aim of this investigation was to characterize those 5-HT receptors present in three different tissues of the common garden snail. Helix aspersa, into one or more of the categories already described for vertebrate 5-HT receptors. Specific 5-HT receptor agonists and antagonists which had been developed and used to help characterize, and subsequently classify, the various types of 5-HT receptor in vertebrates, were utilized in this study. The three preparations from Helix included: i) identified neurones in the visceral ganglion ii) the heart and iii) the pharyngeal retractor muscle (PRM). The action of 5-HT on identified neurones in the visceral ganglion was studied using the electrophysiological techniques of both voltage- and current- damp. Under voltage-clamp conditions the response of the identified neurones to iontophoretic application of 5-HT was seen to be an inward current of approximately 3-10 nA. Under current-clamp conditions the response to 5-HT was an excitatory depolarization leading to the firing of action potentials of approximately 3-15 mV. Both responses showed rapid desensitization to repetitive applications of 5-HT and were blocked by tubocurarine. No specific 5-HT receptor antagonist to this 5-HT response in Helix neurones was found. The action of 5-HT was mimicked by 5-CT and a- Me-5-HT both of which showed similar-sized responses to 5-HT, whereas sumatriptan gave smaller responses than those of 5-HT. 5-HT had a positive inotropic effect on the heart. The excitatory action of 5-HT on the heart was studied using an organ bath methodology with application of the 5-HT receptor agonists and antagonists at suitable concentrations. No specific 5-HT receptor antagonist was found for the cardioexcitatory effect of 5-HT. The full rank order of potency for the 5-HT receptor agonists tested was 5-HT > methylergometrine = ergotamine = 5-CT > -Me-5-HT = sumatriptan > methysergide = 2-Me-5-HT = tryptamine 8-OH-DPAT. 5-HT caused relaxation in the PRM and was found to inhibit, in a dose- dependent manner, acetylcholine (ACh)-induced contraction in the muscle. This inhibition of ACh-induced contraction by 5-HT in the PRM was studied using an organ bath methodology with application of 5-HT receptor agonists and antagonists at suitable concentrations. No specific 5-HT receptor antagonist for the inhibition of ACh-induced contraction was found. The rank order of 5-HT receptor agonist potency was 5-HT > 5-CT > sumatriptan = ergotannine = methysergide >> -Me-5-HT = 2-Me-5-HT. The effect of 5-HT on cyclic adenosine 3',5'-monophosphate (cAMP) levels within Helix heart and pharyngeal retractor muscle (PRM) tissue were monitored in this investigation. 5-HT caused a dose-dependent increase in cAMP both in Helix heart and PRM tissue. The 5-HT receptors within Helix are not readily characterized into any of the categories of 5-HT receptor that have been already classified in vertebrates: Helix 5-HT receptors appear to be unique in the fact that they are unclassifiable in terms of the vertebrate 5-HT receptor classification. The evidence presented in this investigation is discussed in terms of the molecular biology of receptors: this includes the hypothesis that the 5-HT receptors particularly in Helix heart and PRM tissue could be related to a family of G-protein-coupled receptors whereas the neuronal 5-HT receptors in Helix are more likely to be integral to an ion channel.
13
Underwood, G. J. C. "Interactions between freshwater pulmonate snails, macrophytes and epiphytes". Thesis, University of Sussex, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.518005.
Testo completo
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Ash, V. B. "Resistance to shell breaking in two intertidal snails". Thesis, University of York, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379538.
Testo completo
15
Manning, Shawn David. "Susceptibility of Zimbabwean highveld snails to Schistosome infection". Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670270.
Testo completo
16
Peters, Howard. "Cone snails : a significant biomedical resource at risk". Thesis, University of York, 2013. http://etheses.whiterose.ac.uk/5101/.
Testo completoAbstract (sommario):
Gastropod molluscs of the genus Conus (cone snails) occur throughout the world’s tropical coastal waters where they capture their prey of fish, molluscs or worms using a complex battery of neurotoxins. Although these toxins are of major importance to biomedical science, the conservation status of Conus has been largely ignored. I assessed 632 species of Conus to the standards of IUCN Red List of Threatened Species. This revealed 10.6% of species globally are either threatened or near threatened with extinction, with a further 13.8% data deficient but with indicators that suggest substantial cause for concern. Hotspots of endemism, particularly along the Eastern Atlantic found 42.9% of 98 species there at risk. This includes Cape Verde where 53 of 56 species are endemic and mostly restricted to single islands, and where all three critically endangered and four of eleven globally endangered species occur. The rapid transition of the Cape Verdean economy from services to tourism was found to have placed many Conus species at risk from habitat disturbance and marine pollution. Although the Red List yields valuable data, it is primarily focussed on species nearing extinction. However, many wide-ranging species, exposed to considerable anthropogenic impacts, may, through remoteness and/or depth, remain unnoticed and unrecorded for years, invisible to the Red List as their populations decline. To identify such species I explored the overlap of Conus with biogeographic data of human impacts and future threats from ocean acidification and thermal stress. This revealed a further 67 species occurring in high impact zones deserving further status consideration, and pinpointed regions with high concentrations of endemic taxa under potential threat. This reinforced the benefits of approaching threat assessment from a holistic standpoint in addition to the forensic scrutiny offered by the Red List, allowing proactive conservation management to complement its traditional reactive role.
17
Soomro, Noor Mohammad. "Pathology of schistosome infection in mice and vector snails". Thesis, Bangor University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321436.
Testo completo
18
Hoso, Masaki. "Handedness coevolution : predator-prey interaction drives speciation in snails". 京都大学 (Kyoto University), 2008. http://hdl.handle.net/2433/136933.
Testo completo
19
Ho, Wai-hoong, e 何慧紅. "The taxonomy and ecology of land snails in Hong Kong, with particular reference to factors affecting their distribution and populationdynamics". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1994. http://hub.hku.hk/bib/B31211458.
Testo completo
20
Tomba, Abbie Marie Feminella Jack W. "Effects of trematode parasites on habitat use and disturbance response of freshwater snails in the genus Elimia". Auburn, Ala., 2006. http://repo.lib.auburn.edu/Send%2012-15-07/TOMBA_ABBIE_52.pdf.
Testo completo
21
Exton, Samantha Jane. "Natural selection in fossil and recent molluscs". Thesis, University of Liverpool, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366482.
Testo completo
22
Campbell, Gillian. "Molecular evolution and population genetics of Biomphalaria (Mollusca: Gastropoda)". Thesis, University of Aberdeen, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275031.
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23
Hanley, Michael Edward. "The influence of molluscan herbivory on seedling regeneration in grassland". Thesis, University of Southampton, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296377.
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24
Ribeiro, Maria JoseÌ Braga Marques. "Molecular mechanisms of appetitive learning in the pond snail Lymnaea stagnalis". Thesis, University of Sussex, 2002. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247995.
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Babiker, Ismail Elsheikh. "Evaluation of various biomanipulations aimed at controlling freshwater pulmonate snails". Thesis, University of Sussex, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332587.
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Leone, Stacy E. "Predator induced plasticity in barnacle shell morphology /". Abstract Full Text (HTML) Full Text (PDF), 2008. http://eprints.ccsu.edu/archive/00000496/02/1952FT.htm.
Testo completoAbstract (sommario):
Thesis (M.A.) -- Central Connecticut State University, 2008.Thesis advisor: Jeremiah Jarrett. "... in partial fulfillment of the requirements for the degree of Master of Arts in Biology." Includes bibliographical references (leaves 27-29). Also available via the World Wide Web.
27
Wheater, C. P. "Feeding strategies in some predacious Coleoptera". Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253705.
Testo completo
28
Crossley, Michael. "Neural mechanisms of decision making in the pond snail Lymnaea stagnalis". Thesis, University of Sussex, 2014. http://sro.sussex.ac.uk/id/eprint/48861/.
Testo completoAbstract (sommario):
The aim of this thesis was to identify key neural mechanisms underlying decision making in a model invertebrate system, the pond snail Lymnaea stagnalis. Specifically, this was examined with respect to two decision making processes associated with Lymnaea's feeding behaviour; first a stimulus present/stimulus absent perceptual decision making task for selecting between appetitive and consummatory behaviours, second a behavioural choice between ingestion and egestion. A behavioural paradigm was designed in order to study stimulus present and stimulus absent decision making in Lymnaea. The switch between appetitive and consummatory behaviours was used as a read out of the decision. During stimulus absent decisions, the animal made a judgement about the absence of a sensory stimulus and entered into a period of quiescence. During stimulus present decisions the animal switched from the appetitive behaviour into the consummatory behaviour. The decision about the presence of a stimulus was reliant on the tactile cues from the potential food. Importantly the task was amenable for in vitro preparations and the identification of the decision neurons. A candidate stimulus present decision neuron, the ventral trigger neuron (vTN), was identified in the buccal ganglia. vTN received appropriate sensory input and was able to initiate fictive feeding cycles. vTN was able to initiate fictive feeding cycles via monosynaptic connections with feeding central pattern generator (CPG) interneurons. Development of an in vitro paradigm of the stimulus present and stimulus absent decision provided strong evidence that vTN was a stimulus present decision neuron. A stimulus absent decision neuron was identified as the inhibitory interneuron and member of the feeding CPG, N3t. An in vitro paradigm was used to test interactions of the stimulus present decision neuron with the stimulus absent decision neuron. Goal directed behaviours were also shown to lower the threshold of activity needed for vTN to initiate fictive consummatory behaviours, lowering the sensory threshold needed for stimulus present decisions to be made. The neural mechanism of behavioural choice between ingestion and egestion in Lymnaea was characterised using in vivo and in vitro preparations. A novel motor neuron was identified whose phase of firing activity was selectively shifted between the two behaviours. The interneuronal control of ingestion was identified and consisted of previously identified command-like neurons, whereas the interneuronal control of egestion consisted of novel interneurons located in the buccal ganglia. The two networks showed evidence of both dedicated and multifunctional interneurons. The studies presented in this thesis demonstrate that even within the same relatively simple neural network several distinct mechanisms are utilised for different types of decision. These were identified at the level of individual neurons and their synaptic connectivity. Uniquely in these studies, distinct stimulus absent and stimulus present decision neurons were identified in the perceptual decision task and it was also shown that performing the decision making task facilitates the stimulus present decision. This provides fundamental new insights into the neural mechanisms of decision making. The studies also provide a model system for comparison between a form of decision making studied extensively in mammals (perceptual decision making in a stimulus absent/stimulus present task) and a form studied primarily in invertebrates (behavioural choice between two incompatible behaviours), bridging the gap between invertebrate and vertebrate decision making studies.
29
Ciparis, Serena. "Evaluation of the relationships between watershed-scale land use and contaminants in aquatic environments and the use of freshwater snails as indicators of impairment". Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/37815.
Testo completoAbstract (sommario):
The use of manure from animal feeding operations (AFOs) as fertilizer on agricultural land may introduce contaminants to aquatic environments that can negatively affect the health of aquatic organisms. This study utilized a landscape-scale regression-based design to assess the effects of AFOs on contaminant concentrations and resident populations of a pleurocerid snail, Leptoxis carinata, in streams within the Shenandoah River watershed (Virginia, USA). Individual characteristics of L. carinata were also evaluated to provide further understanding of observed population characteristics. In streambed sediment and mollusk tissue, concentrations of the trace element arsenic, used as an additive in poultry feed, were not directly related to watershed densities of AFOs. In-stream concentrations of dissolved nutrients and estrogenic compounds, measured as estrogenic activity, were directly related to watershed densities of AFOs. Population sex ratios of L. carinata varied across study sites, from balanced to female-biased, but were not related to concentrations of estrogenic compounds. However, the spatial variation in population sex ratios, coupled with little variation in site-specific sex ratios across seasons and generations, suggest an influence of site-specific environmental conditions. Individual-level studies of L. carinata revealed that there is an eight month lag between hatching and gametogenesis which could allow disruption of sexual differentiation by environmental contaminants, but further study of the effects of specific contaminants on sexual differentiation in this species is needed. Population densities of L. carinata were related to in-stream nutrient concentrations and landscape sources of nutrients, including AFOs, but none of these factors were directly related to the infection prevalence of digenetic trematodes in L. carinata populations. Although trematode infection rates in L. carinata populations do not appear to be viable indicators of the influence of eutrophic conditions on disease incidence in aquatic organisms, the identification of five types of trematodes in L. carinata populations highlights the utility of this snail species for further investigation of transmission dynamics of trematode parasites in lotic systems.Ph. D.
30
Whitwam, Ross Edward Carleton University Dissertation Biology. "The Covalent modification of phosphofructokinase and pyruvate kinase in the hypometabolic pulmonate Otala Lactea". Ottawa, 1988.
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31
Kistner, Erica Jean. "Adaptive responses and invasion the role of plasticity and evolution in snail shell morphology /". Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Thesis/Spring2009/e_kistner_042509.pdf.
Testo completoAbstract (sommario):
Thesis (M.S. in zoology)--Washington State University, May 2009.Title from PDF title page (viewed on Oct. 09, 2009). "School of Biological Sciences." Includes bibliographical references (p. 77-82).
32
Raymond, Katherine Mary. "Studies on the inter-relationships between Schistosoma species and bulinid snails". Thesis, Bangor University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302958.
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White, Jessica C. "Comparative Bioavailability of Dietary and Dissolved Cadmium to Freshwater Aquatic Snails". Thesis, University of North Texas, 2003. https://digital.library.unt.edu/ark:/67531/metadc4351/.
Testo completoAbstract (sommario):
Heavy metal bioaccumulation in aquatic organisms may occur through direct or indirect uptake routes. Research indicates that the significance of uptake route varies with contaminant and organism exposed. The relative importance of different metal sources in aquatic systems was investigated by exposing freshwater snails to dietary or dissolved sources of cadmium. Snails were exposed to control, contaminated food only, contaminated water only, and contaminated food and water treatments. During the 15-day exposure, samples were taken to determine Cd concentration in snail soft tissue, snail shell, algal food, and overlying water. Analyses of snail soft tissue and shells indicate that exposure route significantly affects Cd concentrations in the tissues. In both cases, dissolved Cd is the primary contributor to metal body burden.
34
Al-Qattan, Nasser M. E. N. A. A. "Interpretation of Oxygen Isotopic Values (d18O) of North American Land Snails". Miami University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=miami1404460805.
Testo completo
35
Lee, Jacqueline S. "The distribution and ecology of the freshwater molluscs of northern British Columbia". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0033/MQ62481.pdf.
Testo completo
36
Chebli, Vivian-Azar. "Proteins of Ilyanassa obsoleta embryos : analysis of delobed embryos and isolated polar lobes". Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61906.
Testo completo
37
Ledger, Mark Edward. "Invertebrate grazing of biofilm in streams of contrasting pH". Thesis, Queen Mary, University of London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266219.
Testo completo
38
Yeung, Chee-yu Alex, e 楊智羽. "Population dynamics and secondary production of a dominant molluscan primary consumer, Sulcospira hainanensis (gastropoda : pachychilidae),in Hong Kong streams and their implications for benthic productivity: y Yeung Alex Chee Yu". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hub.hku.hk/bib/B5043455X.
Testo completoAbstract (sommario):
The lack of any measurements of the secondary production of the prosobranch snail Sulcospira hainanensis (Bröt, 1872) (Pachychilidae), an abundant primary consumer in Hong Kong streams, represents a major gap in our knowledge of the magnitude of benthic productivity in these systems where S. hainanensis constitutes a substantial proportion of community biomass. This study investigated the population dynamics and production of S. hainanensis between February 2011 and February 2012 in 4 Hong Kong streams (2 unshaded and 2 shaded). Annual production by amphibiotic insects was also quantified by emergence traps to evaluate the importance of in-stream production by fully aquatic animals versus that leaving streams in the form of adult aquatic insects. In addition, snail grazing effects on algae and the potential for consequent competitive interactions with benthic insects was compared under different shading conditions and between wet and dry seasons.
Sulcospira hainanensis was ovoviviparous and had balanced sex ratios. Brood size ranged from 52 to 1189, and 3 recruitment episodes were observed in both populations in the one-year study period. Hatchlings reached sexual maturity in 3 – 5 years whereas adults could live for 6 – 12 years. Mean population densities varied from 108.4 to 206.1 individuals m^(-2), while mean biomass was 1003.0 to 4430.2 mg ash-free dry mass (AFDM) m^(-2) and was generally higher in the dry season. Snail production was estimated using the size-frequency, instantaneous-growth (field- and computer-based) and increment-summation (IS) methods, with the IS estimates (1612.8 – 6123.9 mg AFDM m^(-2) 〖year〗^(-1)) considered to most accurately represent production by S. hainanensis. Annual turnover ratios were 1.36 – 2.24 〖year〗^(-1), and production was higher in unshaded streams where growth was more rapid, reflecting higher availability of algal food.
The contribution of S. hainanensis to production by benthic animals as previously estimated in one study site was relatively low (15%) compared with its contribution to total standing biomass (26%). Annual insect emergence varied from 167.5 – 780.2 mg AFDM m-2 year-1, and constituted ~13% of total benthic production in one site, and this preliminary finding suggests that the water-to-land energy flux attributable to emerging insects along tropical Hong Kong streams is rather minor.
The competition effects of S. hainanensis were studied during the dry season of 2012 and the wet season of 2011 by means of snail inclusion-exclusion manipulations. Snails exerted strong effects on algae and insects during the dry season, but did not significantly affect the structure of benthic assemblages. Algae in shaded streams were more severely depleted by snails, though the reduction in snail densities did not lead to increases in insect abundance or biomass. The effects of snails were not detectable during the wet season, when spate-induced disturbances were more frequent and intense. This generally agreed with the harsh-benign hypothesis, which predicts a reduction in the significance of biotic interactions under more disturbed conditions. Therefore, competition between S. hainanensis and insects was important only at base-flow conditions during the dry season.published_or_final_version
Biological Sciences
Master
Master of Philosophy
39
Riley, Elizabeth M. "Interactions between helminth parasites and molluscs". Thesis, University of Aberdeen, 1990. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU545967.
Testo completoAbstract (sommario):
Interactions between two digenean parasites, Diplostomum spathaceum and Schistosoma mansoni , and their respective intermediate snail hosts, Lymnaea stagnalis and Biomphalaria glabrata , were investigated. D.spathaceum infections in juvenile L.stagnalis became patent 9 to 10 weeks post-infection and inhibited initiation of host oviposition. Adult L.stagnalis resisted infection with D.spathaceum . Both juvenile and adult B.glabrata were susceptible to S.mansoni and the infections become patent 5 weeks after infection. B.glabrata infected as juveniles failed to begin egg-laying whilst those infected as adults showed a dramatic reduction of oviposition 4 weeks post-infection, i.e before the onset of patency. Infection with D.spathaceum , but not S.mansoni , resulted in the appearance of three polypeptides (68.3, 40.8 &'38 34.5 kDa) in snail serum. The additional peptides were not directly related to failure of snail reproduction and are probably of parasite origin. Reproductive failure of infected snails was linked to the later stages of cercarial development by a method developed to manipulate infections using the anthelmintic, praziquantel. D.spathaceum and S.mansoni infections were suppressed in their snail hosts following oral treatment with praziquantel. Praziquantel was selective for cercariae and inhibited cercarial shedding of both digenean species for approximately 5 to 6 weeks before recovery. In mature B.glabrata , harbouring 7 week-old infections of S.mansoni , suppression of cercarial shedding was accompanied by temporary recovery of reproduction. Snail fecundity was halted once more 2 weeks prior to resumption of cercarial shedding. Reproductive recovery depended upon the state of infection and maturity of the host at infection. Failure of D.spathaceum to infect adult L.stagnalis was attributed to the more developed and therefore more competent internal defence system of adult snails. Infection of juvenile, immunologically immature, L.stagnalis with D.spathaceum resulted in several changes in the snail immune system and infection seemed to prevent normal development of several facets of snail immunity.
40
Orton, R. A. "The life-history strategies of two species of stream-dwelling freshwater snails". Thesis, University of Reading, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379698.
Testo completo
41
Ip, Chi Ho. "Molecular evolution of egg perivitelline fluid proteins in apple snails (ampullariidae, caenogastropoda)". HKBU Institutional Repository, 2019. https://repository.hkbu.edu.hk/etd_oa/718.
Testo completoAbstract (sommario):
Gastropods are a highly diverse clade of molluscs that includes limpets, snails and slugs, and the only molluscan lineage with members that have successfully colonized land. Amphibious operculate freshwater gastropods, Ampullariidae, exhibit various morphological and physiological adaptations to their respective habitats, which make them ideal candidates for studying the mechanisms underlying adaptive evolution in gastropods. In the last two decades, there have been interests in the diverse reproductive behaviors of ampullariids: while most genera of apple snails deposit their eggs in a jelly mass underwater, two genera (i.e., Pomacea and Pila) deposit calcareous egg clutches above the waterline. The shift from aquatic to aerial oviposition required the concerted evolution of the adult snail's egg laying behavior as well as the composition of the egg. Today, only limited genomic information is available for this ecologically important family, except in the genus Pomacea, which hinders the investigation of its evolutionary history and mechanism. I have, therefore, developed the publicly accessible transcriptome database, AmpuBase, as molecular resources to support various transcriptomic and proteomic analyses. The database comprise de novo transcriptome assembly of eight species that belong to five representative genera of Ampullariidae. For each species there were 20,730 to 35,828 unigenes with predicted open reading frames, with an N50 ranging from 1,320 to 1,803 bp and 69.7% to 80.2% with functional annotation. Since the ability of laying out-of-water eggs is one of the key steps of terrestrialisation for aquatic snails, I analysed the proteome of perivitelline fluid (PVF) for the eggs of Marisa cornuarietis that were laid underwater. The PVF proteome of P. diffusa also investigated to reveal and compare the biochemical adaptation between P. diffusa clade and P. canaliculata clade. Using LC-MS/MS coupled with transcriptome database, I identified a total of 36 and 32 PVF proteins from M. cornuarietis and P. diffusa, respectively. Comparison of PVF proteomes among the aquatic (M. cornuarietis) and three aerial ovipositing ampullariids (P. diffusa, P. canaliculata and P. maculata) showed that the four species all contain several major perivitellins that are important for the nutrition of the embryos. M. cornuarietis invests heavier in protection against pathogens, whereas the unique presence of calcium binding protein and their high albumen gland expression in three Pomacea, implying the importance of the novel acquisition of this protein for forming the calcareous eggshell of terrestrial eggs. I also found the absence of a neurotoxin (PV2) in M. cornuarietis and P. diffusa PVF, indicating this protein was acquired after the divergence between the ancestors of P. diffusa clade and the P. canaliculata clade, and protects P. canaliculata and P. maculata eggs against terrestrial predators. Evolutionary analyses detected the involvement of gene duplication, positive selection and neofunctionalisation in the formation of several major PVF proteins. With the availability of ampullariid genomes and transcriptomes, I conducted an integrated evolutionary analysis of Pomacea PVF with an aim to understand the molecular adaptations underlying the transition from underwater to terrestrial egg deposition. There were many expanded gene families in the New World ampullariids; some of them may be important for their evolution towards terrestrial egg laying. The PV1 oligomer protein was a novel protein acquired by the common ancestor of New World species to nourishing their terrestrial eggs. Meanwhile, gene duplication followed by neofunctionalisation of MACPF-tachylectin paralogs has contributed to the novel acquisition of the toxic PV2 protein in the P. canaliculata species complex. Overall, using Ampullariidae as an example, my study has demonstrated the power of integrative genomics to address various fundamental questions in evolutionary biology. The findings have enhanced our mechanistic understanding of invasion of terrestrial habitats by aquatic gastropods.
42
Griggs, Jennifer Lynn. "Effects of Atrazine and Metolachlor on Snails, Tadpoles, and Their Trematode Parasites". Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/36122.
Testo completoAbstract (sommario):
The widespread use and subsequent release of pesticides into aquatic environments have sparked concerns about how organisms within these aquatic systems are affected by pesticide pollution. While many studies have examined the effects of pesticides on individual organisms, in a series of experiments, I investigated the effects of a pesticide mixture on members of a complex host-parasite system and on host susceptibility to infection. In my first experiment in the laboratory, I examined changes in survivorship when trematode parasites (Echinostoma trivolvis) and their first intermediate host, Planorbella trivolvis snails, were exposed to a low concentration (10 ppb: 15 ppb) and high concentration (85 ppb: 100 ppb) mixture of atrazine and metolachlor, respectively. There was a significant decline in parasite survivorship in the high concentration treatment at 14 hours, while snail survivorship was unaffected across all treatments. In my second experiment, prior to infection, I exposed the parasites and/or second intermediate hosts, Rana clamitans and Rana sylvatica tadpoles, to the pesticide mixtures and examined subsequent infection levels in the tadpoles. The atrazine and metolachlor mixtures had no significant effects on parasite load in the laboratory. Newly shed parasites were more likely than 10 hours old parasites to infect tadpoles, regardless of pesticide exposure. In my final experiment, I utilized outdoor mesocosms to expose parasites, snail hosts, and Rana sylvatica tadpoles to the pesticide mixture, and I examined differences in parasite load within the tadpoles after two weeks. The pesticides had no significant effect on parasite loads in the field. Overall, my findings suggest the atrazine and metolachlor mixtures used in this study had no significant effects on disease dynamics in a system involving Echinostome parasites, snails, and tadpoles.Master of Science
43
Manker, Jaclyn R. "North American Freshwater Snails as Paleoecologic Proxies in Crystal Lake, Medway, Ohio". Wright State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=wright1630342940519865.
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44
Gouveia, Ana Rita Peres Cardoso. "Investigation of the factors affecting the population dynamics of captive Partula snails". Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/9257.
Testo completoAbstract (sommario):
Partula snails, also known as Polynesian tree snails, were first recorded scientifically from Captain Cook's voyage 236 years ago. They are small gastropod molluscs which belong to the order Stylommatophora. Their distribution is focused in the Pacific region where the majority of the species are island endemics. Half the species are found in the Society Islands of French Polynesia where most research has been carried out. Wild populations were almost annihilated following the introduction of a predatory snail, Euglandina rosea, to control the introduced giant African land snail (Lissachatina fulica) which had become an agricultural pest affecting the local economy. In 1987 the Partula Propagation Group (PPG) initiated a worldwide captive breeding programme for Partula snails in an attempt to save them from extinction. In captivity, though, episodes of high mortality have led to the extinction of some species. The causes of these declines are as yet uncertain. This study aimed to investigate the factors that have affected the survival of 15 species (including two subspecies) of Partula snails in captivity. In summary, the results indicate that both environmental factors (temperature, relative humidity and light) and diet (calcium concentration and dog and cat vitamins in the diet) significantly affect the population dynamics of Partula snails. Both excess light and unstable temperatures and humidity had detrimental impacts on the survival and reproductive success of the species. Additionaly, the low concentration of calcium and the addition of dog and cat vitamins in the diet are also significantly detrimental on the survival and reproductive success of Partula gibba. These studies are highly significant because the biology and requirements of Partula snails are poorly understood, and this can jeopardise a successful captive breeding programme and future reintroductions into their natural environment. It is imperative that the factors that have affected the survival rates of snails in captivity for the last 25 years are fully understood. Partula snails face an uncertain future, with the mass mortality episodes observed during the years several species were lost. It is hoped that these findings stimulate further research in this area and can be applied to other species in similar circumstances.
45
Williams, Emily Rose-Margaret. "Parasites and the ecological undead: marine snails and their suite of trematodes". Thesis, The University of Sydney, 2012. https://hdl.handle.net/2123/28920.
Testo completoAbstract (sommario):
The invisible interactions between parasites and their hosts are important elements of the ecology and biology of host populations. Parasites can shape the morphology, distribution, physiology and behaviour of individual hosts - some commonly studied host-parasite interactions often involve gastropods and trematodes. Trematodes can have detrimental effects on their snail hosts, yet many such relationships are relatively unknown. One such relationship is that of the mud whelks, Velacumantus australis, many of which are infected by several species of parasitic trematode. Australian estuaries and lagoons are commonly populated with these snails. Little work has been done, however, on how these snails are affected by their trematodes. My overall aim was to create a more comprehensive picture of the relationship between trematodes and their snail hosts, since it is unknown what is occurring within populations of these snails in Australia. Through dissections and experiments, I described all the species infecting the snails, including those previously unknown to science; quantified infection prevalence within different populations of snails in New South Wales; compared infection with host size, both in situ and through growth of host bodies over time; assayed proteins and lipids from host tissues to quantify energy reserves; and finally, tested whether snails displayed different behaviours depending on infection status. My results show that parasitism varies temporally and on small and large spatial scales, most likely because of recruitment and presence of other hosts. The effects of parasitism on the host body include differences in growth and energy reserves, and appear to be influenced depending on the species of trematode. The activity and locomotory behaviour of snails is also affected by trematode infection, whether the snail has a neighbour, and the infection status of the neighbouring snail. These results show that the relationship between V australis and its trematodes is more complex than predicted and is influenced by dynamic interactions between spatial variability and parasitism. Future experiments with these snails and other snail-trematode relationships in similar systems should include different spatial scales as well as different species of trematodes in order to disentangle the relationships between parasitism and environmental variation.
46
Naranjo-Garcia, Edna. "Systematics and biogeography of the Helminthoglyptidae of Sonora". Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184460.
Testo completoAbstract (sommario):
A study of the Helminthoglyptidae of Sonora was undertaken to determine the extent of their distribution and speciation. As a result, nine new species of Sonorella are described, and new ranges of the known species are given. The status of the family is reviewed and its standing is supported with the analysis of morphological characteristics of several genera. The zoogeography of the family and its distribution are shown. Possible dispersal and isolation mechanisms are discussed in order to explain the present distribution of these snails, and comments on ecological and speciation accounts are offered.
47
Karlsson, Malin. "Analysis of Polycyclic Aromatic Hydrocarbons in Freshwater Snails of Family Lymnaeidae from Patholmsviken". Thesis, Örebro universitet, Institutionen för naturvetenskap och teknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-46338.
Testo completoAbstract (sommario):
Polycyclic aromatic compounds (PAHs) are a group of organic compounds that are very stable and therefore persistent. They can be pyrogenic or petrogenic and PAHs from petrogenic sources are often enriched with alkylated PAHs while pyrogenic sources often contain more of the parent PAH. In Patholmsviken, a bay located near an abandoned woodimpregnating facility, freshwater snails were collected and analysed for PAH16, alkylated PAHs, oxy-PAHs and azaarenes using GC/MS. The concentrations of PAH16 were compared with previous analyses and the results showed that the levels had declined since 2008 and 2013. The ratio between alkylated PAHs and native PAH coincide with what could be expected from a creosote source which consist of more native PAHs. Only one oxy-PAH could be detected and the levels of alkylated PAHs were low. Freshwater snails seem to be a good bioindicator since they meet many of the desired criteria for a suitable biomonitoring organism.Polycykliska aromatiska föreningar (PAH) är en grupp av organiska föreningar som är mycket stabila och därmed långlivade. De kan vara pyrogena eller petrogena, de petrogena källorna är ofta berikad med alkylerade PAHer medan de pyrogena källorna oftare innehåller mer av icke-substituerade PAHer. I Patholmsviken, en vik som ligger bredvid en nedlagd träimpregneringsanläggning, har snäckor samlats in och analyserats för PAH16, alkylerade PAHer, oxy-PAHer och azaarener med hjälp av GC/MS. Koncentrationerna av PAH16 jämfördes med värden från två tidigare analyser och resultaten visade att nivåerna hade minskat sedan 2008 och 2013. Endast en oxy-PAH kunde detekteras och nivåerna av alkylerade PAHer var låga. De låga nivåerna av alkylerade PAH överensstämmer med vad som kan förväntas hitta från en kreosotkälla som avger pyrogena PAHer. Snäckor verkar vara lämpliga att använda som bioindikatorer eftersom de uppfyller många av de kriterier som finns för dessa.
48
Reilly, Stephanie A. "Forecasting the Spread and Invasive Potential of Apple Snails (Pomacea spp.) in Florida". NSUWorks, 2017. http://nsuworks.nova.edu/occ_stuetd/460.
Testo completoAbstract (sommario):
Forecasting the potential range of invasive species is a critical component for risk assessment, monitoring, and management. However, many of these invasive species are not yet at equilibrium which can be problematic for many modelling approaches. Using the climate matching method, MaxEnt, a series of species distribution models (SDMs) and risk analysis maps were created for select apple snail species in Florida: Pomacea canaliculata, P. diffusa, and P. maculata. Apple snails, freshwater gastropods in the family Ampullariidae, are native to South America and were introduced to the United States via the pet trade approximately 40 years ago. These highly invasive species have already been introduced in ten states and established in at least seven. The models and risk analysis in this study show the majority of Florida was at least moderately suitable for all apple snails modeled, with P. maculata posing the greatest threat.
49
Daldorph, Peter W. G. "The role of short chain carboxylic acids in the ecology of freshwater snails". Thesis, University of Sussex, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.568229.
Testo completo
50
Standley, Claire J. "Schistosoma mansoni and Biomphalaria snails in Lake Victoria : distribution, genetics and ecological dynamics". Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/29867/.
Testo completoAbstract (sommario):
Intestinal schistosomiasis, caused by the trematode parasite Schistosoma mansoni, is a disease of major public health importance in the Lake Victoria region. Accurate information pertaining to the disease's distribution can greatly assist in the maintenance and realignment of existing control strategies. Rapid mapping of disease prevalence is reliant on diagnostic technologies; in the case of intestinal schistosomiasis, traditional stool-based methods are beginning to be complimented with new, rapid diagnostic tools. However, these require extensive validation, in a variety of settings, to determine their efficacy and field-utility. Similarly, diagnostic tests are influenced by other factors, such as the level of endemicity of the parasite, or even intraspecific factors such as genetic diversity. Preliminary research has shown S. mansoni to have high levels of genetic diversity throughout East Africa, although its population dynamics within Lake Victoria have never been explored in detail. Local transmission of the parasite is determined by the presence of compatible snails of the genus Biomphalaria. which act as the intermediate host for S. mansoni. As such, basic distribution mapping of the presence and abundance of Biomphalaria around Lake Victoria will better reveal potential risk areas for transmission; these data could also lead to a greater understanding of the specific environmental conditions preferred by Biomphalaria, allowing for predictive mapping of suitable transmission environments. Sophisticated geostatistical tools have facilitated this process, although new, Bayesian models, which have yielded dividends in parasite mapping, have yet to be applied to intermediate host distribution mapping. There is evidence for species-level differences in compatibility with S. mansoni; the taxonomy of Biomphalaria is confused and confusing, with two suspected species being present in Lake Victoria, but these populations have never been subject to detailed classification scrutiny. Similarly, there may be intraspecific effects on transmission compatibility; population level analysis would elucidate patterns of genetic variation across Lake Victoria. Taking both the genetics and ecological preferences of Biomphalaria into consideration, there may be an effect of scale, which should be explored. Patterns that are found to be significant at the level of Lake Victoria may not hold true at a local scale, crucial for the local transmission biology of the parasite. For example, research has suggested that the presence of other gastropods could reduce the abundance of Biomphalaria, through competitive effects. Diversity may influence the transmission of schistosomiasis at the level of the terminal host as well; it is well known that rodents are capable of acting as reservoirs for S. mansoni, as are numerous nonhuman primates. However, within the context of Lake Victoria, non-human primates have rarely been comprehensively surveyed for the disease, despite the obvious implications for conservation, as well as the potential effect on maintaining local transmission cycles even in the face of treatment campaigns. The research presented in the following thesis sought to address the above themes, relating to the dynamics of S. mansoni and Biomphalaria in Lake Victoria. Through a series of four field expeditions to the Ugandan, Tanzanian and Kenyan shorelines of Lake Victoria, data were collected pertaining to the distribution of S. mansoni in school-age children; 27 schools in Uganda were first surveyed for prevalence and intensity of infection. Questionnaires revealed high levels of migration among the school-children, with high levels of itinerancy also associated with increased risk of being infected with S. mansoni and of missing school-based treatment with praziquantel. Later surveys in Tanzania and Kenya compared prevalence of infection as diagnosed by Kato-Katz stool thick smears against a novel, urine-based, rapid diagnostic called the cathodic cirulating antigen (CCA) dipstick. The CCA performed well, with good agreement against the Kato-Katz diagnostic and high sensitivity and specificity in this high-endemicity environment. However, when the CCA tests were used alongside Kato-Katz thick smears in the Ssesse Islands in Uganda, the agreement was not so good, suggesting that different transmission environments may affect the efficacy of diagnostic tests, and moreover, may result in widely discordant treatment recommendations being put forward. Throughout all of these field expeditions, stool samples were also used for hatching of schistosome eggs and miracidia were collected and stored on Whatman® FT A cards for later molecular analysis. Combined with DNA sequences obtained from cercariae from shedding snails and adult worms passaged in the laboratory, genetic material was obtained from 25 sites along the shoreline of Lake Victoria, representative of all three countries. Using both cytochrome oxidase sub-unit 1 (COl) and microsatellite DNA markers, population genetics analyses revealed extremely high genetic diversity, consistent with previous research, but also low levels of population structuring, with no clear geographical patterns. This contrasted with earlier work which had suggested that the populations of S. mansoni ; in Lake Albert and Lake Victoria appeared segregated; the greater and more extensive sampling presented in this thesis revealed a cross-over of haplotypes between the two lakes, potentially associated again with human migration throughout the region, but also suggesting that adaptation and compatibility with local Biomphalaria populations for successful transmission might be less crucial than previously assumed. In order to investigate the distribution and genetics of Biomphalaria, as well as relate these patterns to the transmission of S. mansoni, malacological surveys were carried out at 223 sites across the Lake Victoria shoreline. Two forms of Biomphalaria, based on shell characteristics, were observed; B. sudanica-like snails were commonly associated in marsh-like habitats whereas B. choanomphala-type snails were more usually found in the lake proper. These observations, together with a number of other environmental variables, were statistically tested using multivariate models within a Bayesian inference framework, a method which has never previously been used on snail intermediate host distributions. The models revealed different factors as being Significant predictors of B. sudanica versus B. choanomphala presence, reinforcing the hypothesis of habitat segregation between the two forms. Closer examination of the two forms of Biomphalaria found suggested intermediate shell forms as well as the more easily recognised B. choanomphala-like and B. sudanica-like forms. In order to elucidate the taxonomy of these various forms, a detailed molecular and morphological assessment was carried out on 7 populations of Biomphalaria. Morphologically, principal component analysis (PCA) of shell measurements, aperture outlines and internal anatomy measurements revealed overlapping groupings, supporting the earlier observation of intermediate forms. CrUcially, there were no clear species-level divisions in the genetic data; the groupings that were observed were not significantly associated with those according to morphology. These data combined to imply that the Biomphalaria in Lake Victoria should be considered one species, with two ecophentoypic variants: B. choanomphala var. choanomphala and B. choanomphala var. sudan;ca. Population level analysis of a total of 29 populations revealed significant levels of population structuring with strong geographical patterns; given these local variations, yet also considering the very different patterns observed for S. mansoni, these findings could suggest that local compatibility is less of a restriction on the spread of the parasite than previously thought.