Ploidy state of aquatic macrophytes: Global distribution and drivers

Despite the increasing evidence that ploidy is a factor of importance for environmental adaptation, little work has hitherto been done about cytotype patterns in aquatic plants. We tested a set of hypotheses concerning the drivers of ploidy in macrophyte communities at worldwide scale, and also how ploidy state may be related to other attributes of aquatic plants such as community diversity, species range size and invasiveness. We built a global ploidy database with 1574 species (representing 45.0 % of the known total global pool) and allocated ploidy state to species occurring in 238 10 × 10° gridcells worldwide. We used Boosted Regression Trees Analysis to analyse the relationship of 16 global-scale spatial, landscape, environmental and biotic variables with ploidy state. Our results demonstrate that (1) Polyploid and mixed ploidy species occupied larger geographical ranges than haploid/diploid species. (2) There were contrasting latitudinal patterns between haploid/diploid and polyploid species with polyploidy increasing in importance with distance from the equator, while species richness measures also influenced ploidy state. (3) Climatic factors, especially temperature and evapotranspiration, are congruent with macrophyte species ploidy state, across the planet. Our data support the assertion that increased chromosome number is an adaptation associated with plant survival of harsh environmental conditions, especially in environmentally-stressed high latitudes. Our findings increase the generality of knowledge of the large-scale factors that drive cytotype patterns in vascular plant species at global scale. The ploidy database provides a resource to support further studies about the effects of varying environmental conditions on ploidy state in aquatic plants, at differing scales.