This study describes the effect of the root hemi-parasitic angiosperm Rhinanthus minor on the structure of the communities in which it lives and seeks to elucidate a mechanism through which the parasite acts to effect these changes in the community. Field manipulations reveal that R. minor suppressed the growth of grasses and legumes in a newly sown meadow whilst promoting the forbs within one growing season. In contrast the removal of R. minor from mature meadow plots did not influence their composition. After an additional growing season the parasite did not further influence the composition of the new meadows but removal did begin to benefit the biomass of mature plots. In isolation the parasite caused most damage to grasses whilst leaving legumes and forbs undamaged. Moreover, the parasite performed worst in terms of growth and photosynthesis when attached to the forbs. Consequently the parasite was able to moderate intra-specific competition between grasses and forbs. I thus hypothesised that forbs were able to prevent the parasite form abstracting resources where as grasses could not. Tracer experiments using isotopically e5N) labelled potassium nitrate confirmed this hypothesis showing that more of the resources taken up by the host were stolen by the parasite from grasses than from forbs. There was much variability in the translocation of resources from the legume studied. The reasons underlying the differential uptake of resources were highlighted using histological studies which showed that all of the forbs possessed successful resistance mechanisms to the parasite whilst no successful resistance was observed in the grasses or legumes. Two different resistance mechanisms were observed in the forbs; hypersensitive cell-death at the host-parasite interface and host lignification. I therefore propose that differential host resistance may underlie this parasite's community level effects as forbs possess a resistance capacity that other potential hosts do not.

Made available in DSpace on 2014-06-12T15:54:02Z (GMT). No. of bitstreams: 2 arquivo1953_1.pdf: 1722836 bytes, checksum: 2be769931d2befdf5a296cf78a205f34 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2008 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Baseado, por exemplo, na localização geográfica de um determinado host na Internet, podese oferecer serviços especializados, como: a) páginas web com preferências regionais (e.g. usuários online podem receber propagandas direcionadas ou ter a linguagem para apresentação de conteúdo selecionada automaticamente); b) controle de disponibilidade de dados, de acordo com a localização do usuário (e.g. pode-se restringir o acesso a determinados dados através de políticas regionais e autorização de transações a partir de localidades pré-estabelecidas), c) estudo e análise de tráfego geolocalizado para entender quem se comunica com quem no nível de usuários, regiões e países e identificação de anomalias de roteamento. Os aspectos comuns destas aplicações são a sua dependência em relação a estratégias, denominadas geolocalização. Contudo, alguns destes mecanismos apresentam uma baixa acurácia ou uma estimativa de localização geográfica não-aceitável para determinadas aplicações. Portanto, torna-se de grande importância estudos que melhorem a precisão, bem como a completude das estratégias utilizadas para inferir a geolocalização de hosts na Internet. Este trabalho tem como principais objetivos o estudo sobre as estratégias de geolocalização existentes; a proposta de uma estratégia que melhore a precisão das inferências de localização geográfica de hosts na Internet e a completude dos resultados; e o estudo de tráfego geolocalizado de uma base de dados da rede acadêmica do Estado de Pernambuco. A estratégia desenvolvida, denominada WBG (Whois Based Geolocation), é baseada em buscas whois online e possui uma heurística baseada na ferramenta traceroute

Abstract Female ability to exploit conspecifics in reproduction may have unusual expressions. I studied the reproductive behaviour of the golden egg bug (Phyllomorpha laciniata; Heteroptera, Coreidae) experimentally in the field and in the laboratory. Female golden egg bugs lay their eggs mainly on the backs of conspecific males and other females. Non-parental eggs are often carried. Occasionally, the eggs are laid on the food plant (Paronychia spp; Polycarpea, Caryophyllaceae) of the species but typically, those eggs survive poorly due to egg parasitism and predation. I explored the dependence of female reproduction on conspecific presence and encounter rate. I also studied female current reproductive state (which depends on if she has recently oviposited) in relation to her activity as well as male choice of a female. Female bugs preferred to oviposit on conspecifics when presented with a choice between a bug and a food plant. When alone females often did not lay eggs. Increased encounter rate with others increased female egg laying rate. Survival of carried eggs among bugs did not vary significantly although males received more eggs than females. Females with high current fecundity (mature eggs accumulated to reproductive tract) were more active than females with lower current fecundity (recently oviposited). Females with high current fecundity seemed to search for conspecifics to lay eggs on. Males also preferred to court females with high current fecundity. These females were more likely to oviposit immediately after mating, lowering the risk of female remating before oviposition. To conclude, conspecifics are important egg-laying substrates for female golden egg bugs. Conspecific availability affects female egg laying and the rate of egg production in short term. In particular, males are necessary for egg-laying females and they typically receive unrelated eggs when they court females. Sexual interactions resulting from female polyandry are crucial factors that maintain female egg laying on the backs of males and other females in the unique reproductive system of the golden egg bug.

Recent studies have uncovered a strong effect of host genetic variation on the composition of host-associated microbiota. Here, we present HOMINID, a computational approach based on Lasso linear regression, that given host genetic variation and microbiome taxonomic composition data, identifies host single nucleotide polymorphisms (SNPs) that are correlated with microbial taxa abundances. Using simulated data, we show that HOMINID has accuracy in identifying associated SNPs and performs better compared with existing methods. We also show that HOMINID can accurately identify the microbial taxa that are correlated with associated SNPs. Lastly, by using HOMINID on real data of human genetic variation and microbiome composition, we identified 13 human SNPs in which genetic variation is correlated with microbiome taxonomic composition across body sites. In conclusion, HOMINID is a powerful method to detect host genetic variants linked to microbiome composition and can facilitate discovery of mechanisms controlling host-microbiome interactions.

Staphylococcus aureus is an important opportunistic pathogen in humans and animals. In humans, there has been an increase in community-associated methicillin-resistant Staphylococcus aureus (MRSA) causing disease in healthy humans. The exact evolutionary origins and basis for its recent expansion are not yet clear. In livestock, S. aureus is an important cause of diseases of welfare and economic importance, including bovine mastitis. Molecular typing studies demonstrate that natural populations of S. aureus are highly clonal and largely adapted to a specific host, however there are some lineages that colonise multiple host species. In particular, clonal complex 97 (CC97) is a dominant bovine mastitis-associated lineage which has been isolated from other animal species, and more recently there are increasing reports of CC97 S. aureus from human infections worldwide. The basis for this wide host tropism is currently unknown. In order to investigate the evolutionary origins of S. aureus CC97, 43 strains were selected for whole genome sequencing, isolated from humans, cattle and pigs, from 18 different countries on 4 continents, ranging from 1956 to 2012. Phylogenetic analysis using high quality core genome single nucleotide polymorphisms (SNPs) resolved the single CC97 lineage into host-adapted sublineages, which were likely the result of 2 independent livestock-to-human host jumps estimated to have occurred at least 40 years ago. One of the human sublineages consisted of strains from 4 continents indicating global dissemination since the host jump occurred. In order to investigate the genetic basis for human host adaptation in S. aureus CC97, comparative genomic analysis of mobile genetic elements, nonsynonymous SNPs and small insertions and deletions was performed. Of note, independent acquisitions of genetic elements encoding antimicrobial resistance and specific mediators of human innate immune evasion were identified in the human-adapted S. aureus CC97 strains. These data are consistent with an important role for mobile genetic elements in the host adaptive evolution of S. aureus CC97. Also in the current study, a bovine-associated single locus variant of ST97 (ST71) was identified as a phylogenetic outgroup relative to all other S. aureus CC97 strains examined. Comparative genomic analysis of ST71 strains with representative bovine ST97 strains indicate that ST71 has a mosaic genome. A large region spanning the origin of replication demonstrated closest homology to non-CC97 ruminant-associated genotypes, with the remainder of the genome consistent with an ancestral ST97 genetic background. Recombination detection analysis predicts that one or more large-scale recombination events have occurred in the region that spans the origin of replication, resulting in variation in gene content between ST71 and ST97. The data highlight the potential role of homologous recombination in rapidly generating genomic diversity that might alter the phenotype of strains in the ecological niche of the bovine mammary gland. Overall, the study reveals the evolutionary history of a major pathogenic clone of S. aureus affecting multiple host species, and identifies the genetic events which have contributed to its success.

All filarial nematodes of the family Onchocercidae are parasites of vertebrates and require intermediate insect hosts for completion of their life-cycles. Eighteen genera within this family are known to infect birds but very few of the associated intermediate hosts have been elucidated. Sarconema eurycerca (Wehr) is a filarial nematode of swans and geese. A recent study of S. eurycerca in American Whistling Swans (Cygnus c. columbianus ) has demonstrated that the intermediate insect host is a feather louse, Trinoton anserinum (Fabricius) (Seegar, 1977). The main aim of the present study was to investigate the relationship between S. eurycerca and British swans and to determine whether T. anserinum is the intermediate host of the parasite in this country. A total of 1128 swans (of all species) were examined from sites in Britain, Denmark and Iceland. Infected swans were detected by examining blood samples for larval stages of S. eurycerca (microfilariae) using a new sedimentation technique developed in the study. An overall incidence of 15.0% was recorded with a significantly higher proportion of juvenile swans being infected. The microfilariae of S. eurycerca exhibited a diurnal sub-periodic rhythm within the host, with maximum counts occurring between 11.00 and 19.00 hours in the peripheral blood supply. T. anserinum was found to satisfy all the attributes required of an intermediate insect host. As an obligate ectoparasite, T. anserinum has a close spatial and temporal relationship with the swan. T. anserinum appears to be capable of ingesting microfilarie of S. eurycerca whilst feeding on blood. All developing larval stages of S. eurycerca were found in T. anserinum and the louse was very mobile and capable of transmitting the nematode from one swan to another. Examinations were made of the nematode, its morphology and pathological effects on both heart tissue and blood components of the swan. Significantly higher lymphocyte percentages and lower eosinophil percentages, haematocrit and red blood corpuscle counts were recorded in swans infected with S. eurycerca.

Abstract Study was made of host-guest complexation of neutral crown ethers with five- and six-membered N-heteroaromatic cations and purinium cation. Complexation of tetraphenylborate with selected N-heteroaromatic cations and tropylium cation also was studied. Crown ether complexes were characterized by mass spectrometric and 1H NMR spectrometric methods and by X-ray crystallography. Fast atom bombardment mass spectrometry (FABMS) was used as a prelimary tool to characterize the complexes and electrospray ionization mass spectrometry (ESIMS) was used to confirm the complexation stoichiometry. Crystal structures were determined by X-ray crystallography to study the complexation in solid state, and stability constants were measured in acetonitrile by 1H NMR titration at 30 °C to study the complexation in solution. Mass spectrometric studies indicated preferential 1:1 complexation stoichiometry between crown ethers and N-heteroaromatic cations. Crystal structures of crown ether complexes showed that hydrogen bonding and to a lesser degree cation-π and π-π interactions stabilize the structures in solid state. The values of stability constants for crown ether complexes with N-heteroaromatic cations and purinium cation varied between 10 and 350 M-1. Stability constants were higher for complexes with six-membered N-heteroaromatic cations and purinium cation than for complexes with five-membered cations. The values indicated that hydrogen bonding was the main interaction in solution. Tetraphenylborate formed complexes with four N-heteroaromatic cations and tropylium cation, and reacted with six N-heteroaromatic cations through the displacement of one phenyl group by N-heterocycle to form triphenylboranes. The complexes and displacement products were characterized by 1H NMR spectrometry. Four crystal structures of complexes and three crystal structures of displacement products were resolved. Stability constants of complexes were measured in methanol/acetonitrile (1:1) solution at 30 °C by 1H NMR titration method. The values of stability constants for tetraphenylborate complexes with N-heteroaromatic cations ranged from 10 to 50 M-1. C-H···π and N-H···π interactions were found to stabilize the structures both in solid state and in solution.

M.Sc. (Zoology) / Please refer to full text to view abstract

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The Karoo is an arid inland plateau in the central and northeastern Cape Province of South Africa and is characterised by sparse, stunted vegetation. The vegetation is rich in species, and over large areas species of Pentzia, which are drought-resistant shrubs, are extremely abundant. These plants are food for stock (mainly sheep), and because the larvae of the Karoo caterpillar periodically occur in sufficient numbers to defoliate the plants, they assume pest status. Fully-fed Loxostege frustalis larvae construct cases in the soil beneath their food plants and they overwinter in these cases. A census of the numbers of larval cases accumulated in the soil, conducted from 1975 to 1980, showed that an expanded distribution of the pentzias is responsible for the periodic larval outbreaks. Further, alternate food plants are an important food supply for L. frustalis larvae when they disperse under crowded conditions The census data for L. frustalis were analysed by constructing partial life tables for the life-history period from case construction to moth emergence. The mortality of 'encased larvae' is useful for assessing the impact of the known L. frustalis natural enemies. The most important natural enemies were the braconids Chelonus curvimaculatus Cameron, Macrocentrus maraisi Nixon and the fungus Beauveria bassiana (Balsamo) Vuillemin. The collective responses of all the natural enemies to the density of L. frustalis encased larvae was direct, but undercompensating, so that areas with more pentzias produced more L. frustais. Strategies for immediate measures to alleviate the Karoo caterpillar problem, and for future research, are discussed. It is concluded that reduction of pentzia populations to acceptable levels and/or supplementing pastures with non-host plants of L. frustalis offer the only practical solutions to the Karoo caterpillar problem. Biological control of L. frustalis is dismissed as an option for reducing the pest status of the Karoo caterpillar