Livshultz, Tatyana , Hochleitner, Sonja .
Pollen transfer efficiency in Apocynum cannabinum (Apocynaceae): an evolutionary perspective.
We report the first measurement of pollen transfer efficiency (PTE) in an Apocynaceae species without pollinia. Pollen transfer efficiency (the percentage of removed pollen deposited on conspecific stigmas) is an important component of male fitness and thus selection for PTE may shape the evolution of plant traits. Traits that confer high PTE may be key innovations that lead to elevated species diversity since high PTE may reduce extinction rates by preventing reproductive failure in small fragmented populations. Apocynaceae with pollinia, “milkweeds”, are known for extremely high PTEs (median=20.0%, IQR=21.6%, N=37 species) compared to animal-pollinated angiosperm species with solitary pollen grains (median=0.64%, IQR=1.61%, N=10 species). Aggregated pollen (pollinia and pollen tetrads) and other floral novelties hypothesized to increase PTE have evolved multiple times in Apocynaceae, making them an attractive group for evolutionary studies of floral function. In Apocynum cannabinum, a species with pollen tetrads, we measured pollen removal and deposition from 90 post-anthesis flowers from 18 ramets in 3 populations. Species-level PTE is 7.5%, SD= 0.9%. This falls in the 25th percentile of PTEs measured for milkweed species and is more than twice as high as any reported for animal-pollinated angiosperm species with solitary pollen grains, consistent with predictions from floral morphology that the flowers of A. cannabinum function in much the same way as flowers of milkweeds, but with less precision and efficiency. Total pollen removal is significantly greater for flowers from which two bands of style-head adhesive are missing than for flowers with only one band of style-head adhesive missing, and almost all pollen clumps deposited on stigmas (19 of 20 examined) had all or part of a style-head adhesive band attached, evidence that style-head adhesive bands function as translators for attaching pollen to pollinators. Pollen deposition was bimodal: 47% of flowers received no pollen clumps and 26% received sufficient pollen to pollinate all ovules in an average flower (median=322 ovules, IQR=52, N=11).
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1 - Academy of Natural Sciences of Philadelphia, Botany Department, 1900 Benjamin Franklin Parkway, Philadelphia, PA, 19103-1101, USA
2 - Kohlstattweg 9, Seeon, D-83370, Germany
Presentation Type: Oral Paper:Papers for Topics
Location: 553A/Convention Center
Date: Monday, August 2nd, 2010
Time: 3:00 PM