Do the helminth parasites of wood mice interact?

1. Two published data sets of helminths of the wood mouse Apodemus sylvaticus (L.) were analysed to test the hypothesis that the structure of these component communities is influenced by interactions between species. A range of tests, with differing null models, was applied to tease out the importance of controlling for subgroupings (e.g. sex, age, site, year, season) within the data when searching for significant associations based on prevalence (co-occurrence, presence/absence) or abundance (quantitative associations) data. 2. Significant differences from null models were detected for associations based on prevalence, but when subgroup constraints were taken into consideration, most lost significance. Among three and 15 pair-wise associations possible in data sets 1 and 2, respectively, only that between Trichuris muris and Heligmosomoides polygyrus was not dependent on context, and that between H. polygyrus and Catenotaenia pusilla, while always positive, varied in magnitude among sites of capture. 3. Pair-wise comparisons of abundance revealed three significant associations, only one of which (H. polygyrus with C. pusilla) still remained significant after controlling for quantified extrinsic and intrinsic factors. With increasing burdens of H. polygyrus, mice carried more of other helminth species and this relationship remained significant after controlling for confounding factors. 4. Overall, positive co-occurrences of pairs of helminths of A. sylvaticus were highly context dependent and quantitative associations were weak and not convincing. Therefore, interactions between parasites are unlikely to play a dominant role among the processes that structure the component community of helminths in wood mice, in selected study sites in the south of England.