Résumé
Assessing the impact of natural enemies of plant and animal pathogens on
their host's population dynamics is needed to determine the role of
hyperparasites in affecting disease dynamics, and their potential for use
in efficient control strategies of pathogens. Here we focus on the
long-term study describing metapopulation dynamics of an obligate
pathogen, the powdery mildew (Podosphaera plantaginis) naturally infecting
its wild host plant (Plantago lanceolata) in the fragmented landscape of
the Åland archipelago (southwest Finland). Regionally, the pathogen
persists through a balance of extinctions and colonizations, yet factors
affecting extinction rates remain poorly understood. Mycoparasites of the
genus Ampelomyces appear as good candidates for testing the role of a
hyperparasite, i.e. a parasite of other parasites, in the regulation of
their fungal hosts’ population dynamics. For this purpose, we first
designed a quantitative PCR assay for detection of Ampelomyces spp. in
field-collected samples. This newly developed molecular test was then
applied to a large-scale sampling within the Åland archipelago, revealing
that Ampelomyces is a widespread hyperparasite in this system, with high
variability in prevalence among populations. We found that the
hyperparasite was more common on leaves where multiple powdery mildew
strains coexist, a pattern that may be attributed to differential
exposure. Moreover, the prevalence of Ampelomyces at the plant level
negatively affected the overwinter survival of its fungal host. We
conclude that this hyperparasite may likely impact on its host population
dynamics and argue for increased focus on the role of hyperparasites in
disease dynamics.