How does genome size affect the evolution of pollen tube growth rate, a haploid performance trait?

Premise Male gametophytes of most seed plants deliver sperm to eggs via a pollen tube. Pollen tube growth rates ( PTGR s) of angiosperms are exceptionally rapid, a pattern attributed to more effective haploid selection under stronger pollen competition. Paradoxically, whole genome duplication ( WGD ) has been common in angiosperms but rare in gymnosperms. Pollen tube polyploidy should initially accelerate PTGR because increased heterozygosity and gene dosage should increase metabolic rates. However, polyploidy should also independently increase tube cell size, causing more work which should decelerate growth. We asked how genome size changes have affected the evolution of seed plant PTGR s. Methods We assembled a phylogenetic tree of 451 species with known PTGR s. We then used comparative phylogenetic methods to detect effects of neo‐polyploidy (within‐genus origins), DNA content, and WGD history on PTGR , and correlated evolution of PTGR and DNA content. Results Gymnosperms had significantly higher DNA content and slower PTGR optima than angiosperms, and their PTGR and DNA content were negatively correlated. For angiosperms, 89% of model weight favored Ornstein‐Uhlenbeck models with a faster PTGR optimum for neo‐polyploids, whereas PTGR and DNA content were not correlated. For within‐genus and intraspecific‐cytotype pairs, PTGR s of neo‐polyploids < paleo‐polyploids. Conclusions Genome size increases should negatively affect PTGR when genetic consequences of WGD s are minimized, as found in intra‐specific autopolyploids (low heterosis) and gymnosperms (few WGD s). But in angiosperms, the higher PTGR optimum of neo‐polyploids and non‐negative PTGR ‐ DNA content correlation suggest that recurrent WGD s have caused substantial PTGR evolution in a non‐haploid state.