Orientador: Felipe Wanderley Amorim / Resumo: As plantas oferecem recurso alimentar a muitas espécies animais através de diferentes estruturas. Dentre tais estruturas estão os nectários, que são glândulas multicelulares especializadas na produção e secreção de néctar. Estes nectários podem ocorrer tanto em partes reprodutivas como vegetativas, e podem ser florais ou extraflorais. Entretanto, também podem ser classificados quanto a sua função em relação com a polinização, sendo do tipo nupcial (quando sua função está relacionada à polinização) ou extranupcial (quando sua função está relacionada à defesa). Tocoyena formosa (Rubiaceae) é uma espécie comum do Cerrado, cujos nectários extraflorais são visitados por formigas. Entretanto, T. formosa tem um único nectário que desempenha funções multivalentes, podendo ser tanto nupcial, quanto extranupcial. Adicionalmente, a espécie também atrai formigas aos botões no início da fase de desenvolvimento cujas corolas são abortadas. Neste contexto, para melhor compreender a interação entre T. formosa e formigas, este trabalho teve como objetivos: a) caracterizar as estruturas das distintas fases do nectário da espécie e a composição química de seus açúcares; b) determinar se existe mudança estrutural e/ou química que seja correspondente com o papel ecológico de cada estágio; c) analisar a dinâmica de secreção do néctar em cada um dos estágios de atividade do nectário; e d) quantificar o investimento da planta no recurso para a atração de formigas e o efeito destas no êxito reproduti... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Plants offer food resources to many animal species through different structures. Among such structures are the nectaries, which are multicellular glands specialized in nectar production and secretion. Nectaries can occur in both reproductive and vegetative parts, and depending on the location can be regarded as floral or extra-floral. However, they can also be classified according to their function in relation to pollination, being nuptial (when their function is related to pollination) or extranupcial (when their function is related to the defense). Tocoyena formosa (Rubiaceae) is a common species of the Cerrado vegetation, whose extrafloral nectaries are visited by ants. However, T. formosa has a single nectary that performs multivalent functions, which can be both nuptial and extranuptial. In addition, the species also attracts ants to the flower buds at the beginning of the development, whose corollas are prematurely aborted. In this context, to better understand the interaction between T. formosa and ants, the main goals of this study were: a) to characterize the nectary structure as well as the sugar chemical composition during the distinct stages of the organ; b) assess whether nectary structure and nectar sugar composition present changes which correspond to the ecological function of each stage of the nectary; c) analyze nectar secretion dynamics of each phase of the nectary; and d) quantify plant investment in the attraction of ants and the effectivity of ants in pl... (Complete abstract click electronic access below) / Mestre

Microbes can protect their plant and animal hosts against infection by pathogens, parasites and parasitoids. These ‘defensive microbes' can provide a powerful line of defence beyond the host response and are becoming attractive candidates for disease control. In this thesis, I investigated how defensive microbes can interact with pathogens over evolutionary time by measuring the effects of co-passaging a defensive microbe (Enterococcus faecalis) and a pathogen (Staphylococcus aureus) within the Caenorhabditis elegans model host. In Chapter 1, I found that co-passaging drove the evolution of reduced pathogen virulence as a by-product of adaptation to microbe-mediated defence. Moreover, I show that the mechanism of pathogen resistance to the defensive microbe can determine the direction of virulence evolution. In chapter two, I discovered that the co-passaged defensive microbe and pathogen populations had undergone coevolutionary interactions within host populations via fluctuating selection dynamics. I then showed that these dynamics resulted in patterns of pathogen local adaptation and increased genetic divergence. Finally, in chapter three, I revealed that these coevolutionary interactions significantly affected the costs and benefits of the defensive microbes to their hosts, but that the relationship between these costs and benefits prevented the transition of defensive microbes across the mutualism-parasitism continuum. Together, this thesis uncovers the potential for defensive microbes to shape the evolution of pathogens and demonstrates that defensive microbes can be an evolutionarily dynamic but stable form of host resistance towards infectious disease. As such, the data presented in this thesis have important implications for how we study host-parasite interactions in nature and question our current understanding of virulence evolution, pathogen local adaptation and the origin of defensive microbes.