Aquatic eutrophication promotes pathogenic infection in amphibians

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.amphibian decline ͉ emerging disease ͉ environmental change

Intensive aquaculture selects for increased virulence and interference competition in bacteria

“…Eutrophication of the aquatic environment increases parasitic and bacterial diseases via direct and indirect effects in the food web [41,42]. While the role of eutrophication on F. columnare epidemics is still unclear, the increased nutrient concentrations may support the outside-host growth of this pathogen, giving the more virulent strains a greater advantage (electronic supplementary material, figure S2; see also [43]).…”

Pesticide concentrations in frog tissue and wetland habitats in a landscape dominated by agriculture

“…Pesticides have the potential to increase susceptibility (Mann et al, 2009) while elevated nutrient concentrations have the potential to increase the incidence of disease in amphibian populations (Johnson et al, 2007). On the other hand, studies have documented the relationship between pesticides and susceptibility to infections by trematodes (Rohr et al, 2008).…”

“…Contaminants have the potential to cause lethal effects in amphibians, such as reduced survival or sub-lethal effects such as immunosuppression, malformations, compromised reproduction and reduction in growth and development (Hecnar, 1995;Taylor et al, 2005;Johnson et al, 2007;Gahl et al, 2011;Groner and Relyea, 2011). For example, the herbicide atrazine has the potential to cause immunosuppression in adult northern leopard frogs (Brodkin et al, 2007) and impair sexual development of male frogs (Hayes et al, 2003).…”

“…However, Davidson et al (2007) found no correlation between a common insecticide, carbaryl, and amphibians' susceptibility to the amphibian chytrid fungus (Batrachochytrium dendrobatidis, Bd). Increased eutrophication due to nitrogen based fertilizers, coupled with pesticide application, may cause trophic cascades resulting in increased rates of parasitism in wetlands and has been linked to immunosuppression in amphibians (Brodkin et al, 2007;Johnson et al, 2007). Although a direct link has been made between pesticide exposure and infection by trematodes (Rohr et al, 2008;Kiesecker, 2002), a general understanding of these interactions in the field is lacking because results vary by species and land-use (King et al, 2007).…”

Record of morphological deformities in Corydoras aff. longipinnis in two reservoirs under urban influence in Upper Iguaçu and Southern Coastal basins in Paraná State, Brazil

“…In addition, environmental changes can make populations susceptible to parasites, cause parasite populations to increase, or cause intermediate host populations to increase. The resulting increase in parasitic infestation can cause diseases which in turn result in morphological deformities (Cunningham et al 2005, Johnson et al 2007.…”