Mutualism or parasitism? Nursery pollination of Silene stellata by the noctuid moth Hadena ectypa.
Reynolds, Richard*,1, Fenster, Charles1, Dudash, Michele1, 1 University of Maryland, College Park, MD
ABSTRACT- Nursery pollination of Silene (Caryophyllaceae) by moths of the genus Hadena (Noctuidae) is generally considered to be a negative interaction. However, the sign of the interaction is likely to be context dependent on nursery and co-pollinator community composition, their relative effectiveness, and their relative densities, which vary among populations and/or years. Here we present results from studies of the relative density, efficiency, and effectiveness of the nursery pollinator, Hadena ectypa, and other nocturnal moth and diurnal bee pollinators of its host, Silene stellata. Floral traits (e.g., white flowers, fringed petals, fragrance) and breeding system characters (nocturnal anthesis and stigma receptivity) are consistent with a nocturnal moth pollination syndrome. The nocturnal moths deposit more pollen grains and remove fewer than diurnal bees resulting in higher pollinator efficiency (pollen grains deposited/ pollen grains removed) for moths (0.74%) than bees (0.24%). The frequency of pollen export and the accuracy of pollen delivery to the stigmatic surface is greater for nocturnal than diurnal visitors. Pollinator effectiveness is equivalent between H. ectypa and other nocturnal co-pollinating moths, and co-pollinator density exceeded nursery pollinator density in 2005. The relative effectiveness and abundance data coupled with high levels of seed predation suggests that the interaction between S. stellata and H. ectypa is negative. Quantifying spatio-temporal variation in nursery pollinator density, seed predation, and S. stellata fruit and seed production will allow us to further explore the role of ecological context in causing changes in the sign of the interaction between H. ectypa and its host Silene.
Key words: pollination, Silene, mutualism biology
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