Whole-genome duplication enables rapid evolution of male-biased sex allocation

Sex allocation in hermaphrodites involves a balance between fitness gained through male and female functions. Whole-genome duplication (WGD) might disrupt such a gradually evolved balance, if the relatively instantaneous effects of WGD on cell and organ sizes affect sexual functions differently. We studied sex allocation patterns in intraspecific populations of neo-autotetraploids and their diploid progenitors within Galax urceolata. Floral organ sizes and numbers were measured using light microscopy and genome sizes verified with flow cytometry. Relative to diploids, autotetraploids had proportionally longer sepals and petals, but the same number of flowers, anthers, and ovules per inflorescence. Whole-plant allocation to anther volume increased by 176% but for ovules, only by 70%. Autotetraploids had 33% larger and 88% more pollen, and a 78% higher pollen-to-ovule ratio. In Galax, total allocation to volumes of primary sexual organs increased by a remarkable 213% in autotetraploids relative to diploids, but that surplus was preferentially invested in anthers over ovules. Anther enlargement by WGD supported the evolution of higher pollen production after WGD, as also found in many wild tetraploid species. Floral enlargement by polyploidy can enable both greater pollinator attraction and increased pollen production, traits that may enhance fitness through male function during early polyploid evolution.