Project A09

Responses of metazoan parasite communities to stressor increase and release

Hypothesis 1 Hypothesis 1 ARC 2 ARC 3 ARC 4 ExStream Field studies Invertebrates Fish Parasites Food webs

Project leader

Prof. Dr. Bernd Sures

Project Summary

A multitude of studies underline the pivotal role of parasites for ecological processes supporting the theory that parasite diversity is closely linked to ecosystem functions and integrity. However, it has been poorly studied how parasite diversity is directly or indirectly altered by the increase and release of multiple stressors and how this translates into overall community composition and ecological functioning. Therefore, we will study the effects of stream degradation and restoration on parasite communities and subsequent effects on free-living organisms.

We expect that stressors predominantly affect parasites with complex life cycles, i.e. specialists and heteroxenous parasites, while parasites with simple life cycles (generalists and monoxenous parasites) may increase in abundance. We further expect generalists to colonise restored stream sections first and that communities of free-living species greatly impact the colonization success of parasites. Finally, as parasites will also affect stressor susceptibility of their hosts, we hypothesise that parasitised individuals show a parasite-modulated drift and dispersal behaviour.

To test the above listed hypotheses, samples of macroinvertebrates (snails and arthropods) for the analysis of parasite communities will be obtained from non-degraded, degraded and restored sites (A17, Z02). In cooperation with A11, parasites will be determined in fish (sculpins) and infection data will be correlated to the overall genetic diversity and immune competence of the fish. In cooperation with A12 and A13, we will determine if the trophic position of parasites in a food web will change during phases of stream degradation and recovery. Joint experiments with A08 in the ExStream system will allow for comparing the response of parasitised and unparasitised hosts to experimentally induced stressors. In collaboration with project A16, we will analyse parasitism as a factor driving host dispersal processes. A09 will thus link various experimental and field projects by analysing the response of metazoan parasite communities as well as the role of metazoan parasites as modulators of free-living species’ dispersal during degradation and recovery processes.