Parasitic chytrids could promote copepod survival by mediating material transfer from inedible diatoms |
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Authors: | Maiko Kagami Nico R Helmsing Ellen van Donk |
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Institution: | (1) Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Rijksstraatweg 6, 3631 AC Nieuwersluis, The Netherlands;(2) Department of Environmental Science, Faculty of Science, Toho University, Miyama 2-2-1, Funabashi 274-8510, Japan;(3) Department of Palaeoecology, Institute of Environmental Biology, University of Utrecht, Utrecht, The Netherlands |
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Abstract: | Diatoms form large spring blooms in lakes and oceans, providing fuel for higher trophic levels at the start of the growing
season. Some of the diatom blooms, however, are not grazed by filter-feeding zooplankton like Daphnia due to their large size. Several of these large diatoms are susceptible to chytrid infections. Zoospores of chytrids appeared
to be excellent food for Daphnia, both in terms of size, shape, and quality (PUFAs and cholesterol). Thus, zoospores of chytrids can bridge the gap between
inedible diatoms and Daphnia. In order to examine the effects of diatoms and chytrids on the survival of copepods, we performed one grazing and one survival
experiment. The grazing experiment revealed that the diatom, Asterionella formosa, was not grazed by the copepod, Eudiaptomus gracilis, even after being infected by the chytrid Zygorhizidium
planktonicum. However, carbon and nitrogen concentrations were significantly reduced by E. gracilis only when A. formosa was infected by Z.
planktonicum, indicating that the chytrids might facilitate material transfer from inedible diatoms to the copepods. The survival experiment
revealed that E. gracilis lived shorter with A. formosa than with the cryptophyta Cryptomonas pyrenoidifera. However, the survival of E. gracilis increased significantly in the treatment where A. formosa cells were infected by Z.
planktonicum. Since E. gracilis could not graze A. formosa cells due to their large colonial forms, E. gracilis may acquire nutrients by grazing on the zoospores, and were so able to survive in the presence of the A. formosa. This provides new insights into the role of parasitic fungi in aquatic food webs, where chytrids may improve copepod survival
during diatom blooms. |
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