Potassium stimulates fungal epidemics in Daphnia by increasing host and parasite reproduction

Abstract

As natural enemies, parasites can dramatically harm host populations, and even catalyze their decline. Thus, identifying factors that promote disease spread is paramount. Environmental factors can drive epidemics by altering traits involved in disease spread. For example, nutrients (such as nitrogen and phosphorus) can stimulate reproduction of both hosts and parasites or alter rates of disease transmission by stimulating productivity and nutrition of food resources of hosts. Here, we demonstrate nutrient-trait-epidemic connections between the greatly understudied macronutrient potassium (K) and fungal disease (Metschnikowia bicuspidata) in a zooplankton host (Daphnia dentifera). In a three-year survey, epidemics grew larger in lakes with more potassium. In laboratory assays, potassium enrichment of low-K lake water enhanced both host and parasite reproduction. Parameterized with these data, a model predicted that potassium addition catalyzes disease spread. We confirmed this prediction with an experiment in large mesocosms (6000 L) in a low K-lake: potassium enrichment caused larger epidemics in replicated Daphnia populations. Consequently, the model--data combination mechanistically explained the field pattern and revealed a novel ecological role for the nutrient potassium. Furthermore, our findings highlight the need for further development of theory for nutrient limitation of epidemics. Such theory could help to explain heterogeneous eruptions of disease in space, connect these outbreaks to natural or anthropogenic enrichment of ecosystems, predict the ecological consequences of these outbreaks, and reveal novel strategies for disease management.

Predators and Patterns of Within-Host Growth Can Mediate Both Among-Host Competition and Evolution of Transmission Potential of Parasites

“…In Indiana, we sampled host populations in 17 lakes in Greene, Sullivan, and Monroe Counties every week from August to December during the years 2009-2011 (see Civitello et al 2013 for a list of lakes with geographic coordinates). In Michigan, we sampled 15 lakes every other week in Barry and Kalamazoo Counties from 2003 to 2006 (see Cáceres et al 2006 for more details on the lakes).…”

Poor resource quality lowers transmission potential by changing foraging behaviour

“…), nutrient availability (Civitello et al . ), chemical contaminants (Civitello et al . ), or predator cues (Duffy et al .…”

A Source of Terrestrial Organic Carbon to Investigate the Browning of Aquatic Ecosystems

“…Because it is major constituent of the cytosol and is involved in ion regulation, elevated potassium could affect aquatic biota in different ways. It is generally assumed that potassium limitation is rare [83], but there are instances where enrichment can stimulate the growth of aquatic taxa, including algae [84] and fungal pathogens [85]. In contrast, some studies have suggested the possibility of potassium toxicity.…”