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Abstract Detail

Developmental and Structural Section

Williams, Joseph [1], Taylor, Mackenzie L. [2], O'Meara, Brian C. [1].

Repeated Evolution of Tricellular (and Bicellular) Pollen.

In most seed plants, pollen is dispersed in a sexually immature state, but approximately 30% of flowering plants have evolved pollen that contains two fully formed sperm at anthesis. A classic paper by J. L. Brewbaker (1967: American Journal of Botany 54: 1069-1083) found that such “tricellular pollen” had many parallel, but irreversible, origins from an ancestrally immature and bicellular dispersal state. We modeled the evolution of pollen cell number as a binary state for 2511 species on a time-calibrated angiosperm phylogeny. We used recently-developed comparative phylogenetic methods that accounted for the effect of species diversification rates on character transition rates (BiSSE method), or that allowed variation in transition rates across a phylogeny (HRM method). Seventy-percent of species had bicellular pollen, including 21 early-divergent angiosperms that we studied. BiSSE found a 1.9-fold higher bicellular to tricellular transition rate than in the tricellular to bicellular direction, and bicellular lineages had a 1.8-fold higher diversification rate than tricellular lineages. HRM found heterogeneity in evolutionary rates, with bidirectional transition rates in three of four rate classes. These results show that the tricellular condition is not irreversible, although there was a strong transition bias in the predicted bicellular to tricellular direction. Tricellular lineages have slower rates of evolution than bicellular lineages, since they both diversified slowly and gave rise to bicellular lineages slowly. The slow evolutionary rates of tricellular lineages reflect a linkage between the evolution of sporophyte lifestyles and the developmental lability of male gametophytes.

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Related Links:
Paper in April issue of American Journal of Botany

1 - University Of Tennessee, Department Of Ecology & Evolutionary Biology, 341 HESLER BUILDING, 1406 Circle Drive, KNOXVILLE, TN, 37996-1100, USA, 865/974-6202
2 - Creighton University, Department of Biology, Omaha, NE, 68178, USA

cell cycle
Dollo’s law
Gametophyte evolution
Character evolution
parallel evolution
evolution of development
Pollen development
pollen dispersal
pollen germination
Pollen competition.

Presentation Type: Oral Paper:Papers for Sections
Session: 25
Location: Pines North/Boise Centre
Date: Tuesday, July 29th, 2014
Time: 10:45 AM
Number: 25003
Abstract ID:131
Candidate for Awards:None

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