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Abstract Detail


Reese, John [1], Williams, Joseph H. [1].

The effects of genome size and polyploidy on pollen tube growth rate evolution.

Genome duplication (polyploidy) is a widespread phenomenon in seed plants, but its effects on performance are not well known, and have rarely been studied in the gametophyte generation. In angiosperms, the haploid male gametophyte is highly reduced, functioning largely to develop a pollen tube that delivers sperm directly to the egg and endosperm precursor. Selection on male gametophyte performance is expected to be strong because of pollen competition, the need for accurate fertilization timing, and because of substantial overlap in gene expression between the male gametophyte and the sporophyte. Thus, an important measure of male gametophyte performance is pollen tube growth rate (PTGR), which is generally a function of metabolic rate and tube wall dimensions. Genome duplication might speed PTGR if gene dosage positively affects metabolic rate, whereas it might decrease PTGR if genome size positively affects cell size, causing a need for more wall material per unit of tube length. Here we use comparative analyses to understand the broadscale relationship between genome size and PTGR in seed plants. A phylogenetic tree was generated for 455 species of seed plants using sequences from 16 genes downloaded from GenBank and aligned using PHLAWD. Tree inference was performed in RAxML, and treePL was used for time calibration. The evolution of average maximum PTGRs (speed of first pollen tubes to reach ovules) and genome size were each modelled separately under Brownian Motion (BM) and various Ornstein-Uhlenbeck (OU) processes in OUWie. The evolution of pollen tube growth rate was also modelled between diploids and polyploids using OUwie. Lastly, a phylogenetic least squares regression was performed to test for correlated evolution of genome size (c-value) and PTGR. For PTGRs, nearly 100% of the averaged model weight consisted of OU models in which angiosperm and gymnosperm PTGRs evolved under different selective regimes. Results from genome size and polyploidy analyses will also be presented. Our results show that stabilizing selection tends to act on PTGR, reducing the variance in trait values relative to a Brownian Motion model. This suggests that PTGR is a phylogenetically conservative trait, at least until a shift in selective regime occurs. In contrast, genome size is relatively labile, which may help explain the lack of trend between c-value and PTGR.

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1 - University of Tennessee, Ecology and Evolutionary Biology, Knoxville, TN, 37996, USA

Character Evolution
Comparative Biology
Functional traits
Male Gametophyte
genome size

Presentation Type: Oral Paper
Session: 2, Macroevolution
Location: Fort Worth Ballroom 5/Omni Hotel
Date: Monday, June 26th, 2017
Time: 11:00 AM
Number: 2011
Abstract ID:490
Candidate for Awards:Katherine Esau Award

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