Global-scale drivers of ploidy state in aquatic macrophytes
To determine potential drivers of the global distribution of ploidy in aquatic macrophyte species we allocated ploidy state to 1572 species occurring in 238 10 × 10° gridcells worldwide. Analysis of the relationship of 16 global-scale spatial, landscape, environmental, and biotic variables with ploidy state using Boosted Regression Trees revealed temperature variables and evapotranspiration as the strongest predictors. There were contrasting latitudinal patterns between haploid/diploid and polyploid species, while species richness measures also influenced ploidy state. Polyploid species occupied larger geographical ranges than haploid/diploid species. Mixed ploidy species showed the highest latitudinal range size and maximum latitude of species occurrence. Our findings suggest that increased chromosome number is associated with tolerance of a wider range of environmental conditions in macrophyte species. Mixed ploidy could reflect adaptability to expand geographical occurrence via chromosome number change, with such species predominantly occupying a latitude range intermediate between haploid/diploid and polyploid macrophyte dominance.