The potential of zooplankton in constraining chytrid epidemics in phytoplankton hosts

Thijs Frenken, Takeshi Miki, Maiko Kagami, Dedmer B. Van de Waal, Ellen Van Donk, Thomas Rohrlack, Alena S. Gsell (Corresponding author)

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Abstract

Abstract Fungal diseases threathen natural and man-made ecosystems. Chytridiomycota (chytrids) infect a wide host range, including phytoplankton species that form the basis of aquatic food webs and produce roughly half of Earth's oxygen. However, blooms of large or toxic phytoplankton form trophic bottlenecks as they are inedible to zooplankton. Chytrids infecting inedible phytoplankton provide a trophic link to zooplankton by producing edible zoospores of high nutritional quality. By grazing chytrid zoospores, zooplankton may induce a trophic cascade as a decreased zoospore density will reduce new infections. Conversely, fewer infections will not produce enough zoospores to sustain long-term zooplankton growth and reproduction. This intricate balance between zoospore density necessary for zooplankton energetic demands (growth/survival), and the loss in new infections (and thus new zoospores) due to grazing was tested empirically. To this end, we exposed a cyanobacterial host (Planktothrix rubescens) infected by a chytrid (Rizophydium megarrhizum) to a grazer density gradient (the rotifer Keratella cf. cochlearis). Rotifers survived and reproduced on a zoospore diet, but the Keratella population growth was limited by the amount of zoospores provided by chytrid infections, resulting in a situation where zooplankton survived but was restricted in their ability to control disease in the cyanobacterial host. We subesequently developed and parameterized a dynamical food-chain model using an allometric relationship for clearance rate to theoretically assess the potential of different-sized zooplankton groups to restrict disease in phytoplankton hosts. Our model suggests that smaller-sized zooplankton may have a high potential to reduce chytrid infections on inedible phytoplankton. Together, our results point out the complexity of tri-way interactions between hosts-parasites-grazers, and highlight that trophic cascades are not always sustainable and may depend on the grazer's energetic demand.
Original languageEnglish
Article numbere02900
JournalEcology
Volume101
Issue number1
Early online date23 Sep 2019
DOIs
Publication statusPublished - 2020

Keywords

  • international
  • rotifer
  • trophic cascade
  • density dependence
  • allometric relationship
  • food-chain model
  • Cyanobacteria
  • Plan_S-Compliant-TA

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