1. Hyperparasitism
All living organisms can take part in parasitic relationships, either as
parasites or as hosts (Combes, 2001; Krasylenko et al ., 2021).
Interactions between parasites and their hosts are typically regarded as
closed one-to-one systems. In reality, however, these relationships
involve complex multitrophic interactions (Kiss, 2001). The term
“hyperparasite” refers to an organism that parasitizes another
parasitic organism (Fig. 1). Hyperparasitism has been well documented
for many groups of organisms, mainly insect parasitoids associated with
parasitoid hosts, viruses that parasitize disease-causing protozoans,
and parasitic flowering plants (Grybchuk et al ., 2018; Krasylenkoet al ., 2021; Sullivan, 1987). Hyperparasitism by fungi is poorly
studied, even though it is thought to be rather widespread in nature
(Haelewaters et al ., 2018a, 2021a; Parratt and Laine, 2016; Sunet al ., 2019). As fungi are able to parasitize organisms from
different kingdoms (Moore et al ., 2020), this chapter focuses on
fungal hyperparasites parasitic on both fungal and non-fungal hosts.