Host infection history modifies co-infection success of multiple parasite genotypes

1. Co-infections by multiple parasite genotypes are common and have important implications for host-parasite ecology and evolution through within-host interactions. Typically, these infections take place sequentially and therefore, the outcome of co-infection may be shaped by host immune responses triggered by previous infections. For example, in vertebrates specific immune responses play a central role in protection against disease over the course of life, but co-infection research has mostly focused on previously uninfected individuals. 2. Here, we investigated whether sequential exposure and activation of host resistance in rainbow trout Oncorhynchus mykiss affects infection success and interactions between co-infecting parasite genotypes of the trematode eye-fluke Diplostomum pseudospathaceum. 3. In accordance with earlier results, we show that a simultaneous attack of two parasite genotypes facilitates parasite establishment in previously uninfected hosts. However, we find for the ...