Whole genome duplication enables rapid evolution of male-biased sex allocation in Galax urceolata
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Sex allocation in hermaphrodites is thought to evolve to a balance between fitness gained through male and female function. Whole genome duplication (WGD) might disrupt such gradually evolved patterns, since it has relatively instantaneous effects on sizes, but not numbers, of cells and organs. Here we ask whether sex allocation patterns differ between young neo-autotetraploid populations and their diploid progenitors within Galax urceolata .
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Floral organ sizes and numbers were measured using light microscopy and genome sizes verified with flow cytometry.
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Both cytotypes had the same number of flowers, anthers, and ovules per inflorescence, but floral organ sizes were proportionally longer in autotetraploids relative to diploid progenitors. Whole-plant allocation to volume of anthers increased by 176%, but of ovules only 70%. Autotetraploids produced 33% larger and 88% more pollen.
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WGD is known to double pollen volume, but pollen is biased to size reduction in young natural autotetraploids. In WGD-enlarged anthers, pollen size reduction allows increased pollen number to evolve without changing anther size. A literature review shows that higher pollen production in autopolyploid species is common, but not inevitable. Thus, we conclude that polyploidy can provide a pathway to increased pollen production, which may enhance male fitness during their early evolution.
