A host immune hormone modifies parasite species interactions and epidemics: insights from a field manipulation

• Published in: Proceedings of the Royal Society. B, Biological sciences Vol. 285; no. 1890; p. 20182075
• Main Authors: Halliday, Fletcher W, Umbanhowar, James, Mitchell, Charles E
• Format: Journal Article
• Language: English
• Published: England The Royal Society 07.11.2018
• Subjects: Colletotrichum - physiology; Cyclopentanes - metabolism; Ecology; Festuca - immunology; Festuca - microbiology; Host-Parasite Interactions; Host-Pathogen Interactions; North Carolina; Oxylipins - metabolism; Plant Diseases - immunology; Plant Diseases - microbiology; Plant Immunity; Rhizoctonia - physiology; Salicylic Acid - metabolism; North Carolina; biotic interactions; competition; priority effects; immunity; co-infection; disease ecology
• ISSN: 0962-8452; 1471-2954
• DOI: 10.1098/rspb.2018.2075

Parasite epidemics can depend on priority effects, and parasite priority effects can result from the host immune response to prior infection. Yet we lack experimental evidence that such immune-mediated priority effects influence epidemics. To address this research gap, we manipulated key host immune hormones, then measured the consequences for within-host parasite interactions, and ultimately parasite epidemics in the field. Specifically, we applied plant immune-signalling hormones to sentinel plants, embedded into a wild host population, and tracked foliar infections caused by two common fungal parasites. Within-host individuals, priority effects were altered by the immune-signalling hormone, salicylic acid (SA). Scaling up from within-host interactions, hosts treated with SA experienced a lower prevalence of a less aggressive parasite, increased burden of infection by a more aggressive parasite, and experienced fewer co-infections. Together, these results indicate that by altering within-host priority effects, host immune hormones can drive parasite epidemics. This study therefore experimentally links host immune hormones to within-host priority effects and parasite epidemics, advancing a more mechanistic understanding of how interactions among parasites alter their epidemics.