Most animal species are infected with multiple parasite species; however, the role of interspecific parasite interactions in influencing parasite dynamics and shaping parasite communities has been unclear. Although laboratory studies have found evidence of cross-immunity, immunosuppression and competition, analyses of hosts in the field have generally concluded that parasite communities are little more than random assemblages. Here we present evidence of consistent interspecific interactions in a natural mammalian system, revealed through the analysis of parasite intensity data collected from a free-ranging rabbit (Oryctolagus cuniculus) population, sampled monthly for a period of 23 yr. The wild rabbit plays host to a diverse gut helminth community that reflects the communities seen in other economically important domestic herbivores. These findings suggest that parasite interactions could have profound implications for the dynamics of parasite communities. The efficacy of parasite control programmes could be jeopardized if such interactions are not taken into account. In contrast, a clear understanding of such interactions may provide the basis for the development of more environmentally acceptable methods of parasite control.

Insight into the dynamics of parasite-host relationships of higher vertebrates requires an understanding of two important features: the nature of transmission and the development of acquired immunity in the host. A dominant hypothesis proposes that acquired immunity develops with the cumulative exposure to infection, and consequently predicts a negative relationship between peak intensity of infection and host age at this peak. Although previous studies have found evidence to support this hypothesis through between-population comparisons, these results are confounded by spatial effects. In this study, we examined the dynamics of infection of the nematode Trichostrongylus retortaeformis within a natural population of rabbits sampled monthly for 26 years. The rabbit age structure was reconstructed using body mass as a proxy for age, and the host age-parasite intensity relationship was examined for each rabbit cohort born from February to August. The age-intensity curves exhibited a typical concave shape, and a significant negative relationship was found between peak intensity of infection and host age at this peak. Adult females showed a distinct periparturient rise in T. retortaeformis infection, with higher intensities in breeding adult females than adult males and non-breeding females. These findings are consistent with the hypothesis of an acquired immune response of the host to a parasite infection, supporting the principle that acquired immunity can be modelled using the cumulative exposure to infection. These findings also show that seasonality can be an important driver of host-parasite interactions.

Human impacts, including global change, may alter the composition of soil faunal communities, but consequences for ecosystem functioning are poorly understood. We constructed model grassland systems in the Ecotron controlled environment facility and manipulated soil community composition through assemblages of different animal body sizes. Plant community composition, microbial and root biomass, decomposition rate, and mycorrhizal colonization were all markedly affected. However, two key ecosystem processes, aboveground net primary productivity and net ecosystem productivity, were surprisingly resistant to these changes. We hypothesize that positive and negative faunal-mediated effects in soil communities cancel each other out, causing no net ecosystem effects.

No abstract

Parasitic infections are ubiquitous in wildlife, livestock and human populations, and healthy ecosystems are often parasite rich. Yet, their negative impacts can be extreme. Understanding how both anticipated and cryptic changes in a system might affect parasite transmission at an individual, local and global level is critical for sustainable control in humans and livestock. Here we highlight and synthesize evidence regarding potential effects of ‘system changes’ (both climatic and anthropogenic) on parasite transmission from wild host–parasite systems. Such information could inform more efficient and sustainable parasite control programmes in domestic animals or humans. Many examples from diverse terrestrial and aquatic natural systems show how abiotic and biotic factors affected by system changes can interact additively, multiplicatively or antagonistically to influence parasite transmission, including through altered habitat structure, biodiversity, host demographics and evolution. Despite this, few studies of managed systems explicitly consider these higher-order interactions, or the subsequent effects of parasite evolution, which can conceal or exaggerate measured impacts of control actions. We call for a more integrated approach to investigating transmission dynamics, which recognizes these complexities and makes use of new technologies for data capture and monitoring, and to support robust predictions of altered parasite dynamics in a rapidly changing world.This article is part of the themed issue ‘Opening the black box: re-examining the ecology and evolution of parasite transmission’.