Fungal secondary metabolite biosynthesis – a chemical defence strategy against antagonistic animals?

Analogous to their hypothesized benefits in plants, many fungal secondary metabolites may serve as a chemical shield that fends off fungal feeders or competing saprophagous animals. We review different approaches providing increasing evidence that some secondary metabolites may mediate resistance to antagonistic animals, reducing their negative effects on fungal fitness. Because secondary metabolism is under tight regulatory control, that allows adjustment of secondary metabolite formation to diverse ecological challenges, we argue that natural selection has favoured at least some fungal secondary metabolites and the underlying regulatory machinery through antagonistic animals. Yet, whether animals indeed operate as selective agents contributing to the evolution of secondary metabolites as part of a fungal defence strategy remains elusive. We suggest combining eco-evolutionary concepts and methods with genomic and transgenic tools to close this knowledge gap. We predict an increase in fungal species discovered to be amenable to this functional ecological genomic approach.