Some parasites have evolved to grow on closely related host taxa. These
parasites are known as “adelphoparasites” (Goff and Zuccarello, 1994).
Species of Pythium are often parasitized by species of the same
genus, such as P. acanthium, P. mycoparasiticum, P.
nunn, P. oligandrum, and P. periplocum (Berry et al.,
1993; Deacon, 1976; Deacon and Henry, 1978; Lutchmeah and Cooke, 1984;
Martin and Hancock, 1987; Vesely, 1977). It is also common among
chytrids to be parasitized by other chytrids. Species of the same genus
may be both parasite and host and, in some cases, individuals of the
same species parasitize each other (Frenken et al., 2017;
Karling, 1960). For example, Chytridium parasiticum is a
hyperparasite of Chytridium suburceolatum, which is itself a
parasite on Rhizidium richmondense (Gleason et al., 2014;
Willoughby, 1956). Adelphoparasitism is a common phenomenon among
zoosporic hyperparasites, but it is also known in other taxa, such as in Tyrannicordyceps and Claviceps species (Kepler et
al., 2012).
The most comprehensive taxonomic treatments on zoosporic hyperparasites
were done by Karling (1942a, 1942b) and Sparrow (1960). More studies,
however, are necessary to describe both the diversity of these organisms
and their interactions.