Invasive species are a major threat to biodiversity and human health because they often undergo unregulated population growth, putatively because they have escaped their predators; the enemy release hypothesis. However, parasites are also ‘enemies’ and recent work has shown that invasive species lack a full parasite community. So we ask, “does the reduced parasite community contribute to invasion success?” The first step is to undertake rigorous, replicated experiments that will empirically compare the parasite community of invaders versus their native counterparts. We will examine this with respect to the bank vole, a common woodland rodent in mainland UK that has recently become invasive in Ireland. We will experimentally manipulate specific parasites and simultaneously examine the vole population and parasite community interactions. We will describe the social network of the two populations and quantify the contact rates between bank voles and the native biota. Finally, we will investigate the co-evolutionary changes that occur as a function of changes in the parasite community. We predict that invasive species will adapt to the loss of parasites by investing less in immunity and that this has a genetic basis and so we will investigate “Are there genotypic differences between the native and invaded biota?” and secondly “do invasive species undergo evolutionary compensation of the immune system?” Finally, we draw comparisons between the expected changes in the invasive species immune system and that of the ‘Hygiene Hypothesis’ which states that, in humans, a lack of childhood exposure to infectious agents leads to increased susceptibility to allergic diseases. As such we will investigate “Can invasive rodents be used as a model system for the hygiene hypothesis?” This study comprises an in depth ecological investigation of the role of parasites in ‘enemy release’, using a combination of molecular techniques, field surveys, and ecological experiments.
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