How flatworm parasite communities changed in response to human-induced ecosystem perturbations in Lake Victoria

Abstract

Global change is causing distribution shifts and population declines of countless plants and free-living animals. How parasites are affected by global change is largely unknown, despite their ubiquity and importance for ecosystem functioning (e.g. regulation of host populations, increase of food web connectivity). Human-induced environmental changes are expected to alter parasite abundance and host-parasite interactions (e.g. spillover to novel host species), but the direction of such changes is unclear. Lake Victoria, the youngest of the African Great Lakes, is a biodiversity hotspot that experienced simultaneous drastic anthropogenic changes: multiple invasions (e.g. Nile perch), eutrophication and overfishing. We use historical fish collections – harboring a hidden parasite collection – to test whether parasite abundance and host range changed in response to anthropogenic changes in Lake Victoria. We analysed ectoparasite infection in 13 cichlid fish species, representing 7 eco-morphological groups, sampled between 1973 and 2014. Overall parasite abundance, but not parasite diversity, declined after impacts on Lake Victoria. Most ectoparasite species are declining, while few others are increasing in abundance, indicating that parasite species respond differently to ecosystem disturbances. The host range of most ectoparasitic flatworms changed, as they disappeared from some host species and colonized few new host species that they did not infect before ecosystem changes in Lake Victoria. This may suggest that ecosystem disturbances favor host switching. Since changes that have occurred in Lake Victoria are also occurring in other ecosystems, our results suggest that we can use flatworm parasites as sentinel for ecosystem health, which might contribute to better strategies for linking conservation and ecosystem health.