Niche Position Mediates the Effect of Polyploidy on Geographic Range Size in Clarkia

Aim Polyploidy has been proposed to result in greater geographic range size in plants because it increases the capacity for adaptation to novel environments; however, the proposed relationship is not found across clades. By contrast, the large genome constraint hypothesis predicts that larger genomes constrain the niche, leading to similar niches among related polyploids, while the habitat area hypothesis predicts range size is constrained by niche position (the geographic frequency of niche space). We mechanistically evaluated the links between these hypotheses to assess factors influencing polyploid range size and distribution. Location Western North America. Taxon Clarkia (Pursh). Methods Using comparisons between allopolyploids and their progenitors in the genus Clarkia , we tested if polyploids have larger geographic ranges and parallel climatic niche shifts. We also evaluated whether biogeographic patterns of polyploid frequency are predicted by climatic variables and climatic rarity. Lastly, we examined how polyploid niche shifts influenced niche position and breadth and tested whether these variables predicted range size. Results Polyploid range size was not significantly different from progenitors, and polyploids exhibited diverse niche shifts relative to progenitors. Across the entire genus, polyploids were slightly more common in cooler, wetter and more geographically common climates. Variation in polyploid range size was better explained by niche position than breadth. Main Conclusions The results are inconsistent with polyploids having increased adaptive capacity compared to diploids, or parallel niche shifts. However, polyploid ranges were predicted by niche position but diploids were not, perhaps reflecting greater colonization potential. The overall distribution of polyploids in Clarkia was also consistent with variation in factors that may influence formation and establishment.