Abstract Detail

Reproductive Processes

Ison, Jennifer [1], Jackson, Evan [2], Page, Maureen [3], Stevens, Mia [2], Zelman, Zeke [2], Wagenius, Stuart [4].

Measuring pollinator effectiveness in composites: A case study with Echinacea angustifolia and native bees.

Over 60% of flowering plant species have a genetic self-incompatibility mechanism that requires the transfer of unrelated pollen to fertilize ovules. In many plants, bees are the primary pollen vector, and bee-pollinated plants are often visited by more than one species. To determine how effectively a bee species pollinates a plant, biologists often measure a suite of traits, including per-visit seed set, pollen deposition, pollen removal, and overall visitation rate. However, some of these traits, such as pollen deposition, might not accurately quantify how a visit affects plant reproductive fitness, especially in a uniovulate species where each flower has one ovule. Most species in one of the largest plant families, Asteraceae, are both self-incompatible and uniovulate; therefore it is important to understand how differences in pollinator behavior affect plant fitness.
In this talk, we synthesize results from five pollinator effectiveness studies in Echinacea angustifolia (Asteraceae). We measured per-visit seed set (n=207), pollen removal (n=183), pollen deposition (n=183), and genetic diversity of donors of conspecific pollen carried (n=99) and deposited (n=43) by native bees in western Minnesota. We used microsatellite markers and paternity analysis to estimate diversity. We also present results where we hand-crossed Echinacea with varying sized pollen loads to quantify the relationship between pollen deposition and seed set (n= 60). We found that pollen deposition rates per visit did not differ among pollinator taxa. However, the coneflower specialist, Andrena rudbeckiae, set significantly more seeds per visit and removed significantly more pollen than the smaller generalist bee taxa (including Augochlorella sp., Agapostemon sp., Halictus spp. and Lasioglossum spp.) and a similarly sized specialist, Melissodes spp. Although Andrena bees do not deposit more pollen per visit, results indicate that they carry more diverse loads of conspecific pollen and distribute more pollen to receptive stigmas than the other bees. Interestingly, Andrena bees are found only in large populations of Echinacea, and their absence from smaller fragmented populations could contribute to observed pollen limitation in small patches. Our results illustrate that a pollinator’s behavior on composite flowerheads and the genetic diversity of its pollen load are likely more important for plant fitness than how much pollen it deposits per stigma.

1 - The College Of Wooster, Biology Department, 1189 Beall Ave., Wooster, OH, 44691, United States
2 - The College of Wooster, Biology Department, 1189 Beall Ave, Wooster, OH, 44691, United States
3 - University of California Davis, Ecology and Evolution, Davis, CA, 95616, USA
4 - Chicago Botanic Garden, Conservation Science, 1000 Lake Cook Road, Glencoe, IL, 60022, United States

Keywords:
Pollinator effectiveness
plant-animal interactions
Paternity analysis
pollen load size
Echinacea
Native bees
Seed set
Asteraceae.

Presentation Type: Oral Paper
Session: REP1, Reproductive Processes 1
Location: San Luis 2/Starr Pass
Date: Wednesday, July 31st, 2019
Time: 11:30 AM
Number: REP1014
Abstract ID:774
Candidate for Awards:None