Changes in parasite community structure may elucidate causes for ecosystem decline in Lake Victoria

Abstract

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). Lake Victoria, the youngest of the African Great Lakes, is a biodiversity hotspot that experienced drastic anthropogenic changes since the 1950s: multiple invasions (e.g. Nile perch), eutrophication, overfishing. Such ecosystem perturbations occurred simultaneously and led to a rapid decline of biodiversity (halving haplochromine species in few decades) and to an overall reduction in complexity, with consequences also on human health (e.g. emerging infectious diseases). Although parasites contribute to maintain ecosystem health, it is often overlooked how parasite community structure changes in response to ecosystem changes. We expect that low host specificity and host switches are favoured in disturbed ecosystems (we already found indications for this pattern in cichlid fish of Lake Victoria). We aim to understand if recent changes in host specificity of monogenean parasites in Lake Victoria resulted from a natural state of the lake or if it has been recently induced by human disturbances. We use historical collections to detect recent changes in the structure of fish parasites in Lake Victoria. To disentangle which perturbation (eutrophication, Nile perchpredator invasion) mainly caused such changes, we use a space-for-time approach in which we model parasite shifts across lakes that share parasite species as well as closely related cichlids but that differ in disturbance. Since perturbations that have occurred in Lake Victoria are also occurring in other ecosystems, we can use the changes in host ranges of parasites as sentinel, to better monitor and hence conserve ecosystem health elsewhere.