Early colonization of Protea flowers enable dominance of competitively weak saprobic fungi in seed cones, benefitting their hosts

Persistence of ecologically similar fungi in a restricted floral niche

Fungi in the genera Knoxdaviesia and Sporothrix dominate fungal communities within Protea flowerheads and seed cones (infructescences). Despite apparently similar ecologies, they show strong host recurrence and often occupy the same individual infructescence. Differences in host chemistry explain their host consistency, but the factors that allow co-occupancy of multiple species within individual infructescences are unknown. Sporothrix splendens and K. proteae often grow on different senescent tissue types within infructescences of their P. repens host, indicating that substrate-related differences aid their co-occupancy. Sporothrix phasma and K. capensis grow on the same tissues of P. neriifolia suggesting neutral competitive abilities. Here we test the hypothesis that differences in host-tissues dictate competitive abilities of these fungi and explain their co-occupancy of this spatially restricted niche. Media were prepared from infructescence bases, bracts, seeds, or pollen presenters of P. neriifolia and P. repens. As expected, K. capensis was unable to grow on seeds whilst S. phasma could. As hypothesised, K. capensis and S. phasma had equal competitive abilities on pollen presenters, appearing to explain their co-occupancy of this resource. Growth of K. proteae was significantly enhanced on pollen presenters while that of S. splendens was the same as the control. Knoxdavesia proteae grew significantly faster than S. splendens on all tissue types. Despite this, S. splendens was a superior competitor on all tissue types. For K. proteae to co-occupy infructescences with S. splendens for extended periods, it likely needs to colonize pollen presenters before the arrival of S. splendens.