Aquatic eutrophication promotes pathogenic infection in amphibians

TLDR

Eutrophication of aquatic ecosystems, driven by nitrogen and phosphorus enrichment, is a widespread environmental change linked to disease emergence, including the trematode *Ribeiroia ondatrae* that infects birds, snails, and amphibian larvae, causing severe deformities and mortality, yet definitive evidence and mechanistic understanding have been lacking. The study experimentally links eutrophication to disease in a multihost parasite system. Eutrophication promotes amphibian disease by increasing infected snail host density and boosting per‑snail production of infectious parasites. Eutrophication increases algal production, snail host density, and infection intensity in amphibians, reduces amphibian survival, and has broad ecological significance given projected eutrophication and parallels to other pathogens.

Abstract

The widespread emergence of human and wildlife diseases has challenged ecologists to understand how large-scale agents of environmental change affect host-pathogen interactions. Accelerated eutrophication of aquatic ecosystems owing to nitrogen and phosphorus enrichment is a pervasive form of environmental change that has been implicated in the emergence of diseases through direct and indirect pathways. We provide experimental evidence linking eutrophication and disease in a multihost parasite system. The trematode parasite Ribeiroia ondatrae sequentially infects birds, snails, and amphibian larvae, frequently causing severe limb deformities and mortality. Eutrophication has been implicated in the emergence of this parasite, but definitive evidence, as well as a mechanistic understanding, have been lacking until now. We show that the effects of eutrophication cascade through the parasite life cycle to promote algal production, the density of snail hosts, and, ultimately, the intensity of infection in amphibians. Infection also negatively affected the survival of developing amphibians. Mechanistically, eutrophication promoted amphibian disease through two distinctive pathways: by increasing the density of infected snail hosts and by enhancing per-snail production of infectious parasites. Given forecasted increases in global eutrophication, amphibian extinctions, and similarities between Ribeiroia and important human and wildlife pathogens, our results have broad epidemiological and ecological significance.