5. Ecological role of fungal hyperparasitism
Although a common phenomenon in nature, the real impacts of
hyperparasitism on the ecology and evolution of the organisms involved
and its cascading effects throughout food webs is understudied. In the
broad sense, hyperparasites are analogous to predators, where the
secondary hosts (primary parasites) act as herbivores and the primary
hosts replace primary producers. Therefore, as predators, hyperparasites
are able to shape ecosystem stability through top–down cascades
(Parratt and Laine, 2016). Hyperparasitic fungi also influence the
dynamics of the interactions between the primary hosts and the primary
parasites, increase the complexity of the food webs, and play a
significant role in regulating population sizes of either partner
(Gleason et al., 2014; Sandhu et al., 2021). By decreasing
the fitness of their host, hyperparasites may essentially exert a net
positive effect on the fitness of the primary host (Northrup et
al., 2021; Sandhu et al ., 2021). However, a convincing
conceptual framework is lacking, and tractable model systems to study
hyperparasitic interactions in natural populations are scarce (Péter et al., 2022; Parratt and Laine, 2016).
It is hypothesized that zoosporic parasites have a role in the structure
and function of aquatic food webs, by lengthening food chains and carbon
paths. As their life cycles are shorter, zoosporic hyperparasites also
increase and accelerate the energy flow among trophic levels, by
producing biomass in the form of zoospores and zoosporangia that enter
the food web contributing different types of energy for predators
(Gleason et al., 2014).
The range of interactions among hyperparasites, their hosts (i.e., the
secondary hosts), and the primary hosts is wide and complex, and
sometimes difficult to establish (Gleason et al., 2014; Kiss,
2001). Studies on host specificity in hyperparasitic fungal systems are
scarce (but see Barnett and Lilly, 1958; Jeffries and Young, 1978), and
those examining all three trophic levels in the same analysis are even
rarer. One recent study analyzed the ecological interactions among the
three levels of the multitrophic network among bats, bat flies, and
microfungi and found that bat flies are much more host specific at the
community-level compared to their Laboulbeniales hyperparasitic fungi
(de Groot et al., 2020).