Population invasiveness in an insect ectoparasite: The ecological aspects of host-parasite relationship

The ecological role of host-parasite interactions in determining population invasiveness of temperate parasites has remained unclear. We provide a novel attempt to explain differential invasion success of ectoparasite populations by their life-history traits that may arise from divergent co-evolution with local hosts. The model species, the deer ked (Lipoptena cervi), has bimodal distribution in Northern Europe; the eastern population has rapidly invaded to arctic areas by exploiting only one host species (the moose) whereas the western population with two host species (the moose and the roe deer) has remained stable at southern latitudes. According to the results, individual life histories in the invasive population were closely linked to cold adaptations; they were larger and had higher cold tolerance and shorter development compared to those in the stable population. Within the stable population, individuals produced on roe deer performed better in cold than those produced on moose, but lower roe deer densities seem to prevent further spread. The main finding was that exploring life-history variation with respect to different host species is important to determine population invasiveness in insect ectoparasites. The role of host densities, as well as host-related factors contributing to ectoparasites’ invasion success via off-host performance will be discussed.