Parasitism without frontiers: Infection variability of an intermediate host across multiple spatial scales

Background. Parasites are heterogeneously distributed in intermediate host populations, but how this variability changes between multiple geographic scales remain unclear. Here, we test whether in a complex host-parasite system developing in sandy shores, the high spatiotemporal variability in the physical structure of these habitats will lead to comparatively high variability in parasitosis observed at the local- (i.e. few metres) and meso-scale (i.e. tens of km), relative to the regional scale (several 100s of km).

Methods. Here, we analyse the spatial variability of acanthocephalan parasites infecting decapod molecrabs according to a hierarchical design spanning more than 500 km of the southern-central shore of Chile. We predicted that the local effects could potentially influence the host-parasite interaction by generating a large amount of between-site heterogeneity in parasitosis and thus, to improve our understanding of the development of epidemic and infectious processes.

Results. The analysis of generalized mixed-effect models showed that the spatial variability in parasitosis (i.e. probability of infection, parasite burden, prevalence, mean intensity, and mean abundance) was smallest at the regional scale. On the other hand, the largest amount of spatial variability of most measures of parasitosis was observed at the meso-scale. Prevalence, however, displayed similar (and high) levels of variation at meso- and local-scales.

Conclusions. We suggest that parasite infection could be related with abiotic factors that determine habitat physical stability, such as seasonal morphodynamic of sandy shores. Thus, local environmental filters can have strong and deterministic effects on the regulation of this complex host-parasite system across spatial scales.