Lin, Chia-Hua , Klips, Robert .
Pollination ecology of Asclepias sullivantii, a Midwestern prairie endemic plant that depends on exotic honey bees for pollination.
The Sullivant's milkweed (Asclepias sullivantii, Family Apocynaceae) is a self-incompatible, clonal plant endemic to prairie remnants of the Great Lakes region in North America. We studied pollinator abundance and species assemblage and pollen limitation in the Killdeer Plains Wildlife Area in Wyandot County, Ohio. To determine if A. sullivantii was predominantly pollinated by diurnal or nocturnal visitors, we conducted pollinator exclusion experiments with umbels only exposed to natural visitors during daytime, during nighttime, or both for three consecutive days. We then examined these flowers for polliniarium removal and deposition as indicators of pollination activities. We marked 100 pairs of plants similar in size for supplemental pollination experiments. We hand-pollinated three flowers on one plant of each pair and marked three flowers of the same age on the same umbel and on the other plant respectively as controls. During the days when pollinator exclusions were performed, we recorded the number of insect visitors and flowers probed by each visitor on 2 - 3 fresh umbels for 8 minutes near each marked pair between 9am - 6pm. The number of flowering umbels within 2.5 m radius was also counted. Pollinators of A. sullivantii were predominantly diurnal. Over 65% of flowers exposed to daytime visitors had at least 1 pollinarium removed or deposited whereas 11% of flowers had polliniaria removed and near zero deposited by nocturnal visitors. We observed on average 4.1 visitors per umbel (SD 2.66, range 0 - 13) and 5.5 (SD 2.13) flowers probed per visitor during 8-minute observations. The number of pollinators increased with the number of flowering umbels nearby. Honey bees (Apis mellifera) made up 99% of pollinators observed. Other day-time pollinators (i.e., species carrying pollinia) included Bombus spp., Xylocopa virginica, Megachile sculpturalis, and lepidopterans. Supplemental pollination did not have a significant effect on the initiation of fruit development in A. sullivantii; approximately 60% of flowers in both supplemental and control treatments showed apparent ovary growth, compared to non-pollinated flowers, two weeks after petals had withered. However, most developing fruits were aborted and less than 10% of flowers had mature fruit in late summer. Sexual reproduction of A. sullivantii was not limited by pollinators. Factors such as abiotic resources, herbivory, or the availability of genetically compatible mates may impose stronger constraints to fruit production than pollen limitation alone.
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1 - The Ohio State University, Evolution, Ecology and Organismal Biology, 318 W 12th Avenue, Columbus, OH, 43202, USA
2 - Ohio State University, Evolution, Ecology And Organismal Biology, 1465 MT VERNON AVE, MARION, OH, 43302, USA
Presentation Type: Poster:Posters for Topics
Location: Battelle South/Convention Center
Date: Monday, July 9th, 2012
Time: 5:30 PM