Ecology and evolution of host/parasite interactions

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Parasitism is the most common lifestyle on earth. One hallmark of the phenomenon is the complex and intimate interplay that exists between host and parasite to meet their survival and reproduction needs. Although the outcome often involves conflict between two antagonists, many outcomes can be interpreted as a compromise that meet the contrasting aims of the two partners. We often do not know where particular host-parasite interactions fit on this continuum, making it difficult to interpret how evolution will proceed in 'new' host/parasite combinations that so often dominate our anthropogenic habitats. I use a combination of laboratory manipulations, phylogenetic analyses, field work, and modern molecular tools to study the interplay between hosts and parasites. In our main model system, we use common minnows and their brain-encysting flukes to evaluate host response strategies on the one hand, and parasite exploitation strategies on the other. These worms have an obligate feeding phase within brain tissue that reduce the hosts' physiological and behavioural performance. We are now combining phylogenetic comparisons and experimental exposures to track the evolution of the larval feeding stage and testing for life-history trade-offs with other stages in the life-cycle. Within this same system, we will combine laboratory and field experiments to assess the extent to which hosts can minimize the costs of infection by avoiding infective stages all-together. Here, we ask whether fish can detect 'fear factor' associated with infection and then learn to respond via anti-parasite behaviours that reduce risk. In addition to exploiting host resources, many parasites exploit host behaviours to meet their transmission needs. We have a poor understanding of underlying mechanisms. One spectacular example involves the larval stages of a fluke that infects the brains of ants, causing them to ascend vegetation and clamp-on during cold hours of the day. We will use modern proteomics tools involving both parasite and host tissue to uncover the mechanisms leading to the altered behaviours of the 'zombie ants'.