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Abstract Detail

The Evolution of Pollen Performance

Williams, Joseph [1].

Pollen performance from a deep historical perspective.

Pollen performance is ultimately a measure of how effectively the male gametophyte delivers sperm to the egg. Pollen performance traits are thought to evolve rapidly due to the pervasive effects of haploid selection, which can be intensified by pollen competition (i.e. relative pollen performance). Competition-strengthened haploid selection is also expected to increase rates of sporophyte evolution due to the overlap in gene expression between gametophyte and sporophyte generations. Such a scenario is said to be most apparent in flowering plants, which have much faster diversification rates than other seed plant lineages. Here I evaluate the pollen competition hypothesis using comparative analyses of extant early-divergent and derived flowering plant lineages. If pollen competition has been important in shaping angiosperm diversity, one prediction is that traits that speed pollen performance should track the appearance of traits that increase the potential for competition and vice versa. I considered two performance traits, pollen germination speed and pollen tube growth rate (PTGR). I show that structural traits of flowers that favor intense pollen competition have varied considerably through time. The arena for pollen competition among early angiosperms was mostly within stigmatic tissue or secretions, rather than within a transmitting tract of a style. Floral traits favoring stronger competition at the level of pollen tube growth within a style were not common until after the origin of modern monocots and eudicots. Pollen germination speeds of early-divergent angiosperms are much faster than in other seed plants, and are near their maximal speed relative to angiosperms as a whole. Pollen tube growth rates of early-divergent angiosperms, however, are very slow relative to other angiosperms. An ancestral reconstruction based on over 400 species indicates that PTGR was ancestrally very slow, followed by a gradual expansion in rates over time away from the left wall of slow PTGR. Rate slowdowns also occurred. “Superfast PTGRs” (> 10 times faster than the angiosperm median), have originated independently at least 13 times in highly nested groups of both monocots and eudicots. The broad-scale historical pattern of sequential accumulation of traits favoring stronger pollen competition matched by gradual increases in pollen performance (and vice versa) is consistent with the pollen competition hypothesis.

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1 - University Of Tennessee, Department Of Ecology & Evolutionary Biology, 341 HESLER BUILDING, 1406 Circle Drive, KNOXVILLE, TN, 37996-1100, USA, 865/974-6202

none specified

Presentation Type: Symposium or Colloquium Presentation
Session: SY03
Location: Snake/Boise Centre
Date: Monday, July 28th, 2014
Time: 1:30 PM
Number: SY03001
Abstract ID:563
Candidate for Awards:None

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