Article

Parasitic chytrids: their effects on phytoplankton communities and food-web dynamics

Toho University Department of Environmental Science, Faculty of Science Miyama 2-2-1 Funabashi 274-8510 Japan
Hydrobiologia (impact factor: 1.78). 04/2012; 578(1):113-129. DOI:10.1007/s10750-006-0438-z pp.113-129

ABSTRACT Many phytoplankton species are susceptible to fungal parasitism. Parasitic fungi of phytoplankton mainly belong to the Chytridiomycetes (chytrids). Here, we discuss the progression made in the study of chytrids that parasitize phytoplankton species. Specific
fluorescent stains aid in the identification of chytrids in the field. The established culturing methods and the advances
in molecular science offer good potential to gain a better insight into the mechanisms of epidemic development of chytrids
and coevolution between chytrids and their algal hosts. Chytrids are often considered to be highly host-specific parasites,
but the extent of host specificity has not been fully investigated. Chytrids may prefer larger host cells, since they would
gain more resources, but whether hosts are really selected on the basis of size is not clear. The dynamics of chytrids epidemics
in a number of studies were partly explained by environmental factors such as light, temperature, nutrients, pH, turbulence
and zooplankton grazing. No generalization was made about the epidemic conditions; some state unfavorable conditions for the
host growth support epidemic development, while others report epidemics even under optimal growth conditions for the host.
Phytoplankton is not defenseless, and several mechanisms have been suggested, such as a hypersensitivity response, chemical
defense, maintaining a high genetic diversity and multitrophic indirect defenses. Chytrids may also play an important role
in food webs, because zoospores of chytrids have been found to be a good food source for zooplankton.

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Keywords

algal hosts
 
chytrids
 
chytrids epidemics
 
coevolution
 
environmental factors
 
established culturing methods
 
fungal parasitism
 
genetic diversity
 
host growth support epidemic development
 
host specificity
 
host-specific parasites
 
hypersensitivity response
 
larger host cells
 
molecular science offer good potential
 
multitrophic indirect defenses
 
others report epidemics
 
parasitize phytoplankton species
 
phytoplankton species
 
progression
 
zooplankton grazing