HOST PARASITE INTERACTIONS BETWEEN FRESHWATER PHYTOPLANKTON AND CHYTRID FUNGI (CHYTRIDIOMYCOTA)¹

Abstract

Some chytrids are host‐specific parasiticfungithat may have a considerable impact on phytoplankton dynamics. The phylum Chytridiomycota contains one class, the Chytridiomycetes, and is composed of five different orders. Molecular studies now firmly place the Chytridiomycota within the fungal kingdom. Chytrids are characterized by having zoospores, a motile stage in their life cycle. Zoospores are attracted to the host cell by specific signals. No single physical–chemical factor has been found that fully explains the dynamics of chytrid epidemics in the field. Fungal periodicity was primarily related to host cell density. The absence of aggregated distributions of chytrids on their hosts suggested that their hosts did not vary in their susceptibility to infection. A parasite can only become epidemic when it grows faster than the host. Therefore, it has been suggested that epidemics in phytoplankton populations arise when growth conditions for the host are unfavorable. No support for such a generalization was found, however. Growth of the parasitic fungus Rhizophydium planktonicum Canter emend, parasitic on the diatom Asterionella formosa Hassal, was reduced under stringent nutrient limitation,because production and infectivity of zoospores were affected negatively. A moderate phosphorous or light limitation favored epidemic development, however. Chytrid infections have been shown to affect competition between their algal hosts and in this way altered phytoplankton succession. There is potential for coevolution between Asterionella and the chytrid Zygorhizidium planktonicum Canter based on clear reciprocal fitness costs, absence of overall infective parasite strains, and possibly a genetic basis for host susceptibility and parasite infectivity.

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

“…Zoospores of Z. planktonicum, a parasite of three Synedra species, sometimes loosely adhered to A. formosa, but germ tube intrusion was never observed (Doggett & Porter, 1995). Since Z. planktonicum is a well-known parasite of A. formosa (see Ibelings et al, 2004), the findings of Doggett & Porter (1995) also indicated that host selection in Z. planktonicum was confined to either Synedra or Asterionella, as reported by Canter & Jaworski (1986) and Canter et al (1992).…”

“…This paper complements and builds on information summarized in an earlier review . We refer the taxonomy and life cycle of chytrids to Ibelings et al (2004), and to Chytrid Fungi Online: (http://www.bama.ua.edu/~nsfpeet) where recent updates of chytrids taxonomy can be found.…”

High habitat-specificity in fungal communities in oligo-mesotrophic, temperate Lake Stechlin (North-East Germany)

“…Like Monchy et al (2011), we observed similar communities in all of the water samples (Littoral, Pelagic, and Above Sediment). The greater number of OTUs per read abundance may originate from a rare fungal parasite community , whereby parasitic chytrids can recruit for temporally variable infection opportunities such as may occur over time scales of a few weeks (e.g., Ibelings et al 2004;Alster and Zohary 2007).…”

Parasitic chytrids could promote copepod survival by mediating material transfer from inedible diatoms

“…In lakes, diatoms are often infected by parasitic chytrids (Van Donk & Ringelberg, 1983;Ibelings et al, 2004;Kagami et al, 2007a). Chytrids infections seem to be most common in large phytoplankton species that are fairly resistant to grazing by zooplankton (Sommer, 1987;Kagami et al, 2007a).…”