Polyploidy impacts population growth and competition with diploids: multigenerational experiments reveal key life history tradeoffs

Abstract

O_LIEcological theory predicts that early generation polyploids ("neopolyploids") should quickly go extinct owing to the disadvantages of rarity and competition with their diploid progenitors. However, polyploids persist in natural habitats globally. This paradox has been addressed theoretically by recognizing that reproductive assurance of neopolyploids and niche differentiation can promote establishment. Despite this, the direct effects of polyploidy at the population level remain largely untested even though establishment is an intrinsically population-level process. C_LIO_LIWe conducted population-level experiments where investment in current and future growth was tracked in four lineage pairs of diploids and synthetic neopolyploids of the aquatic plant Spirodela polyrhiza. Population growth was evaluated with and without competition between diploids and neopolyploids across a range of nutrient treatments. C_LIO_LIAlthough neopolyploid populations produce more biomass, they reach lower population sizes, and have reduced carrying capacities when growing alone or in competition across all nutrient treatments. Thus, contrary to individual-level studies, our population-level data suggest that neopolyploids are competitively inferior to diploids. Conversely, neopolyploid populations have greater investment in dormant propagule production than diploids. C_LIO_LIOur results show that neopolyploid populations should not persist based on current growth dynamics, but high potential future growth may allow polyploids to establish in subsequent growing seasons. C_LI