Infection outcomes under genetic and environmental variation in a host-parasite system: Implications for maintenance of polymorphism and the evolution of virulence

Virulence (the harm to the host during infection) is the outcome of continuous coevolution between hosts and parasites. This thesis adds to a growing body of work on host-parasite interactions, and describes experiments that study the effects of variation in the genetic and the environmental contexts of infection. All of them focus on interaction between the planktonic freshwater crustacean Daphnia magna and a naturally occurring parasite, the spore-forming bacterium Pasteuria ramosa. I show that elevated minimum temperatures that facilitate parasite growth drive natural epidemics of this parasite. I also demonstrate that the expression of infection traits in P. ramosa is temperature-dependent in a genotype-specific manner [genotype-by-environment (GxE) interactions]. These GxE interactions could maintain polymorphism through environment-dependent selection. Next, I test if GxG interactions for infectivity can be altered by environmental variation (GxGxE interactions), and find that this trait is quite robust to thermal variation. Infectivity is also more important in determining parasite fitness relative to the production of transmission stages, highlighting the importance of considering natural infection routes, an aspect sometimes overlooked in studies of host-parasite systems. Another experiment under different food and temperature regimes showed evidence for environment-dependent virulence-transmission relationships, a fundamental component of virulence evolution models. Lastly, I show that variation in temperature does not increase the cost to the host of resisting infection

Non-linear disease tolerance curves reveal distinct components of host responses to viral infection

The ability to tolerate infection is a key component of host defence and offers potential novel therapeutic approaches for infectious diseases. To yield successful targets for therapeutic intervention, it is important that the analytical tools employed to measure disease tolerance are able to capture distinct host responses to infection. Here, we show that commonly used methods that estimate tolerance as a linear relationship should be complemented with more flexible, nonlinear estimates of this relationship which may reveal variation in distinct components such as host vigour, sensitivity to increases in pathogen loads, and the severity of the infection. To illustrate this, we measured the survival of Drosophila melanogaster carrying either a functional or non-functional regulator of the JAK-STAT immune pathway (G9a) when challenged with a range of concentrations of Drosophila C virus (DCV). While classical linear model analyses indicated that G9a affected tolerance only in females, a more powerful nonlinear logistic model showed that G9a mediates viral tolerance to different extents in both sexes. This analysis also revealed that G9a acts by changing the sensitivity to increasing pathogen burdens, but does not reduce the ultimate severity of disease. These results indicate that fitting nonlinear models to host health–pathogen burden relationships may offer better and more detailed estimates of disease tolerance

Carry on caring:Infected females maintain their parental care despite high mortality

Parental care is a key component of an organism’s reproductive strategy that is thought to trade-off with allocation toward immunity. Yet, it is unclear how caring parents respond to pathogens: do infected parents reduce care as a sickness behavior or simply from being ill or do they prioritize their offspring by maintaining high levels of care? To address this issue, we investigated the consequences of infection by the pathogen Serratia marcescens on mortality, time spent providing care, reproductive output, and expression of immune genes of female parents in the burying beetle Nicrophorus vespilloides. We compared untreated control females with infected females that were inoculated with live bacteria, immune-challenged females that were inoculated with heat-killed bacteria, and injured females that were injected with buffer. We found that infected and immune-challenged females changed their immune gene expression and that infected females suffered increased mortality. Nevertheless, infected and immune-challenged females maintained their normal level of care and reproductive output. There was thus no evidence that infection led to either a decrease or an increase in parental care or reproductive output. Our results show that parental care, which is generally highly flexible, can remain remarkably robust and consistent despite the elevated mortality caused by infection by pathogens. Overall, these findings suggest that infected females maintain a high level of parental care, a strategy that may ensure that offspring receive the necessary amount of care but that might be detrimental to the parents’ own survival or that may even facilitate disease transmission to offspring

Genotype and sex-based host variation in behavior and susceptibility drives population disease dynamics

Host heterogeneity in pathogen transmission is widespread and presents a major hurdle to predicting and minimizing disease outbreaks. Using Drosophila melanogaster infected with Drosophila C virus as a model system, we integrated experimental measurements of social aggregation, virus shedding, and disease-induced mortality from different genetic lines and sexes into a disease modelling framework. The experimentally measured host heterogeneity produced substantial differences in simulated disease outbreaks, providing evidence for genetic and sex-specific effects on disease dynamics at a population level. While this was true for homogeneous populations of single sex/genetic line, the genetic background or sex of the index case did not alter outbreak dynamics in simulated, heterogeneous populations. Finally, to explore the relative effects of social aggregation, viral shedding and mortality, we compared simulations where we allowed these traits to vary, as measured experimentally, to simulations where we constrained variation in these traits to the population mean. In this context, variation in infectiousness, followed by social aggregation, was the most influential component of transmission. Overall, we show that host heterogeneity in three host traits dramatically affects population-level transmission, but the relative impact of this variation depends on both the susceptible population diversity and the distribution of population-level variation

AVALIAÇÃO DO ESTADO DE CONSERVAÇÃO DE NASCENTES EM MICROBACIAS HIDROGRÁFICAS

O estudo de nascentes em microbacias hidrográficas é um importante instrumento de gestão na conservação e preservação dos recursos hídricos visando à produção de água, tanto em quantidade quanto em qualidade. Diante desse desafio, o presente artigo avalia o estado de conservação das nascentes da microbacia do Córrego Ibitinga, localizada no município de Rio Claro, SP. A metodologia adotada abordou o estado de conservação com base em parâmetros macroscópicos de avaliação. Os parâmetros selecionados permitiram avaliar de maneira integrada, os impactos físicos, biológicos e socioeconômicos que afetam as nascentes. Com a aplicação do Índice de Impacto Ambiental em nascentes, os parâmetros foram mensurados e o tratamento estatístico dos dados permitiu a classificação das nascentes em cinco níveis de conservação: ótimo, bom, razoável, ruim e péssimo. Os resultados demostraram os parâmetros mais expressivos para os processos de degradação nas nascentes avaliadas e a frequência de ocorrência dos impactos em relação aos níveis de conservação. As nascentes apresentaram inúmeros aspectos de degradação, sejam eles por ação antropogênica direta ou indireta. Das 39 nascentes estudadas, 75% estão concentradas nas três piores classes. Os resultados permitiram concluir que as nascentes avaliadas apresentaram alto nível de degradação, e que o estado de conservação das nascentes é inerente à proximidade com estradas e ausência de proteção e de vegetação, sendo estes os impactos mais frequentes

The route of infection determines Wolbachia antibacterial protection in Drosophila

International audienceBacterial symbionts are widespread among metazoans and provide a range of beneficial functions. -mediated protection against viral infection has been extensively demonstrated in In mosquitoes that are artificially transinfected with (wMel), protection from both viral and bacterial infections has been demonstrated. However, no evidence for -mediated antibacterial protection has been demonstrated in to date. Here, we show that the route of infection is key for -mediated antibacterial protection. carrying showed reduced mortality during enteric-but not systemic-infection with the opportunist pathogen -mediated protection was more pronounced in male flies and is associated with increased early expression of the antimicrobial peptide , and also increased expression of a reactive oxygen species detoxification gene (). These results highlight that the route of infection is important for symbiont-mediated protection from infection, that can protect hosts by eliciting a combination of resistance and disease tolerance mechanisms, and that these effects are sexually dimorphic. We discuss the importance of using ecologically relevant routes of infection to gain a better understanding of symbiont-mediated protection

Current knowledge and future prospects of lima bean (Phaseolus lunatus)-rhizobia symbiosis

Lima bean (Phaseolus lunatus) is an important species of the genus Phaseolus for human consumption in tropical regions. The seeds are important source of protein for people from South America, Africa and Mexico. In addition, as a legume plant, lima bean presents the ability to perform the biological nitrogen fixation (BNF) through the symbiosis with nitrogen-fixing bacteria. The studies about diversity and efficiency of lima bean-rhizobia symbiosis have increased worldwide, mainly in Latin America. These studies have shown Bradyrhizobium and Rhizobium as the main symbionts, although Sinorhizobium, Mesorhizobium and Allorhizobium have been found associated with lima bean. Also, there is a large variation in the efficiency of N fixation by the current isolates of rhizobia and some rhizobia have presented high capability for fixing N. This review aims to explore the studies about diversity and efficiency of rhizobia in symbiosis with lima bean.Lima bean (Phaseolus lunatus) is an important species of the genus Phaseolus for human consumption in tropical regions. The seeds are important source of protein for people from South America, Africa and Mexico. In addition, as a legume plant, lima bean presents the ability to perform the biological nitrogen fixation (BNF) through the symbiosis with nitrogen-fixing bacteria. The studies about diversity and efficiency of lima bean-rhizobia symbiosis have increased worldwide, mainly in Latin America. These studies have shown Bradyrhizobium and Rhizobium as the main symbionts, although Sinorhizobium, Mesorhizobium and Allorhizobium have been found associated with lima bean. Also, there is a large variation in the efficiency of N fixation by the current isolates of rhizobia and some rhizobia have presented high capability for fixing N. This review aims to explore the studies about diversity and efficiency of rhizobia in symbiosis with lima bean

Estatuto de Roma do Tribunal Penal Internacional: Comentários

Excerto [A importância do Tribunal Internacional Penal, vulgarmente conhecido por TPI, tem dado origem a muitas conferências e debates sobre a sua estrutura e funcionamento, sobre a natureza e os elementos dos crimes que, por força do seu Estatuto, lhe cabe julgar e ainda sobre o seu papel no próprio combate à prática desses crimes pelos responsáveis máximos – políticos e militares – dos Estados, bem como por aqueles que por ordens ou instruções destes ou por iniciativa própria no âmbito de políticas violadoras das leis dos conflitos armados, promotoras de “mass murders” ou de causação de sofrimento desumano de populações inteiras.

Potencial de inseticidas botânicos no controle de Ulomoides dermestoides (Coleoptera: Tenebrionidae)

O uso constante de inseticidas químicos no controle de pragas de grãos armazenados pode representar um aumento nos casos de resistência de pragas a inseticidas, além de problemas de ordem social e ambiental. O objetivo da pesquisa foi analisar em laboratório, a atividade de extratos de erva-de-santa-maria (Chenopodium ambrosioides), angico (Anadenanthera colubrina), eucalipto (Corymbia citriodora), crisântemo (Chrysanthemum cinerariaefolium) e mamona (Ricinus communis) sobre larvas de último ínstar e adultos do besouro do amendoim, Ulomoides dermestoides (Coleoptera: Tenebrionidae). Para cada tratamento foram realizadas 10 repetições, cada qual relacionada a um recipiente plástico contendo 10 g de grãos de amendoim misturados com 500 mg de determinado inseticida botânico, com posterior inserção de 10 imaturos ou 10 adultos por recipiente. A mortalidade foi avaliada no sétimo, décimo quarto e vigésimo primeiro dia após a aplicação dos tratamentos (DAA). Aos 21 DAA foi observada mortalidade de imaturos acima de 94% para todos os tratamentos. O extrato botânico de C. ambrosioides ocasionou mortalidade total de adultos aos 7 DAA, seguido de R. communis (94 ± 2,98%) e C. cinerariaefolium (84 ± 5,62%), com mortalidade acima de 99% aos 14 DAA. Os extratos de C. ambrosioides, C. cinerariaefolium e R. communis apresentam elevada atividade inseticida sobre larvas de último ínstar e adultos de U. dermestoides, enquanto que A. colubrina e C. citriodora são potenciais inseticidas botânicos a imaturos de U. dermestoides