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Transgressive phenotypes and generalist pollination in the floral evolution of Nicotiana polyploids

Abstract

Polyploidy is an important driving force in angiosperm evolution, and much research has focused on genetic, epigenetic and transcriptomic responses to allopolyploidy. Nicotiana is an excellent system in which to study allopolyploidy because half of the species are allotetraploids of different ages, allowing us to examine the trajectory of floral evolution over time. Here, we study the effects of allopolyploidy on floral morphology in Nicotiana, using corolla tube measurements and geometric morphometrics to quantify petal shape. We show that polyploid morphological divergence from the intermediate phenotype expected (based on progenitor morphology) increases with time for floral limb shape and tube length, and that most polyploids are distinct or transgressive in at least one trait. In addition, we show that polyploids tend to evolve shorter and wider corolla tubes, suggesting that allopolyploidy could provide an escape from specialist pollination via reversion to more generalist pollination strategies.

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Figure 1: Side and front floral morphology of N. tabacum and section Polydicliae polyploids and their diploid progenitors.
Figure 2: Distribution of Nicotiana accessions in the floral limb shape morphospace and in tube length and width.
Figure 3: Allotetraploid sections and their diploid progenitors in the floral limb morphospace and in tube length and width.
Figure 4: Directional distance of polyploid means from the progenitor midpoint in floral limb shape and corolla tube length and width.
Figure 5: Distance from the polyploid mean to the progenitor midpoint against estimated polyploid age for floral limb shape, corolla tube length and corolla tube width.

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Acknowledgements

We thank K. Yoong Lim, A. Kovařík, C. Mhiri and I. T. Baldwin for providing us with synthetic polyploids and homoploids. This work was supported by the Natural Environment Research Council (NE/C511964/1 to A.R.L. and M.C.) and the Overseas Research Students Awards Scheme to E.W.M.

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E.M., M.C., S.K., A.R.L. and S.L. designed the research. E.M. collected the data and performed most of the analyses. S.L. performed analyses in Mathematica. E.M., A.R.L. and S.L. wrote the manuscript with help from M.C., S.K. and A.L.

Corresponding author

Correspondence to Steven C. Le Comber.

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The authors declare no competing financial interests.

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Supplementary Figures 1-3 and Supplementary Table 1. (PDF 2193 kb)

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McCarthy, E., Chase, M., Knapp, S. et al. Transgressive phenotypes and generalist pollination in the floral evolution of Nicotiana polyploids. Nature Plants 2, 16119 (2016). https://doi.org/10.1038/nplants.2016.119

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