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Transmission and temporal dynamics of anther‐smut disease (Microbotryum) on alpine carnation (Dianthus pavonius)

Bruns, Emily L., Antonovics, Janis, Carasso, Valentina, Hood, Michael
The journal of ecology 2017 v.105 no.5 pp. 1413-1424
Dianthus, Microbotryum, adults, disease prevalence, extinction, field experimentation, greenhouse experimentation, hosts, juveniles, models, plant pathogens, pollen, pollinating insects, population dynamics, sexually transmitted diseases, smut diseases, spores, sterilizing, temporal variation
Theory has shown that sterilizing diseases with frequency‐dependent transmission (characteristics shared by many sexually transmitted diseases) can drive host populations to extinction. Anther‐smut disease (caused by Microbotryum sp.) has become a model plant pathogen system for studying the dynamics of vector‐ and sexually transmitted diseases: infected individuals are sterilized, producing spores instead of pollen, and the disease is spread between reproductive individuals by insect pollinators. We investigated anther‐smut disease in a heavily infected population of Dianthus pavonius (alpine carnation) over an 8‐year period to determine disease impacts on host population dynamics. Over the 8 years, disease prevalence remained consistently high (>40%), while the host population numbers declined by over 50%. The observed rate of vector transmission to reproductive, adult hosts was inadequate to explain the high disease prevalence. Additional density‐dependent aerial transmission to highly susceptible juveniles, indicated from experimental field and greenhouse studies, is likely to play a key role in maintaining the high disease prevalence. Epidemiological models that accounted for the mixed transmission mode predicted an eventual decline in disease. Synthesis. Our results demonstrate that high prevalence of a sterilizing disease does not necessarily drive host populations towards extinction and also highlights the importance of demographic studies for establishing the presence of alternative transmission modes.