Outcomes of infection are shaped by the host, the parasite, and their environment – but to what extent?
Epidemiological traits in helminth infections of sticklebacks: incorporating evolutionary and ecological perspectives in the study of helminth immune modulation in vertebrate hosts
Epidemiological traits are shaped through effects of the host, the parasite and by their interaction (Figure 1 shows a theoretical illustration of this assumption). The relative contribution of each of the interaction partners may differ along the infection process and depends on the coevolutionary history. Different environments may select for different defence strategies among host populations, which results in immunological heterogeneity (Lazzaro et al., 2009; Graham, 2013). Here, we assessed virulence patterns of a vertebrate host-parasite association on a large geographic scale to test to what extent heterogeneous environments may cause immunological heterogeneity.
We hypothesized that different co-evolutionary trajectories of three-spined sticklebacks (Gasterosteus aculeatus) and their specific cestode parasite Schistocephalus solidus could be seen by specific virulence patterns on a geographic scale. Our data indeed provide evidence that differences in parasite prevalence can cause immunological heterogeneity and that parasite size, a proxy for virulence and resistance, is, on a geographic scale, determined by main effects of the host and the parasite and less by an interaction of both genotypes.