Temporal changes in the flatworm parasite communities of Lake Victoria cichlid fishes in response to ecosystem changes

Abstract

Species interactions are particularly crucial for ecosystem health and for conservation in face of global change. Human-induced environmental changes may influence the host-parasite interactions and may lead parasites to expand their host range (i.e. spillover to novel host species). Although parasites contribute to maintain ecosystem health, it is often overlooked how parasite community structure changes in response to ecosystem changes. We investigate this in flatworms parasitizing cichlid fish in Lake Victoria. 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 recent and historical fish collections to assess whether the communities of parasitic flatworms changed after such ecosystem perturbations in Lake Victoria. We analysed flatworm parasite infection in 12 cichlid fish species, representing 7 eco-morphological groups, sampled between 1973 and 2014. We identified 6 species of monogeneans (1 Gyrodactylus and 6 Cichlidogyrus, which 4 are new to science) and 2 species of copepods. An overall decrease in parasitic flatworm diversity was not observed. Instead, some flatworm parasite species are declining, while others are increasing in abundance, indicating that parasite species respond differently to ecosystem disturbances. Moreover, some flatworm species are becoming more generalists, infecting hosts 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, we can use flatworm parasites as sentinel for ecosystem health, which might contribute to better strategies for linking conservation and ecosystem health.