Fine-scale patterns and drivers of ploidy state in lentic and lotic macrophyte assemblages across the world

To investigate whether patterns of ploidy state variation known to occur in macrophytes at broad global scales can be detected at finer site scale, we examined macrophyte assemblages present in 1239 individual inland lentic and lotic waterbodies sampled from 2000 onwards. The sites include lakes and reservoirs, rivers and streams, slow-flowing or static water bodies associated with rivers (such as oxbows), man-made channels, and temporary or ephemeral lentic waterbodies in 22 countries worldwide. The latitude range for these sites was 10.58–68.40° N and from 0.01 to 54.88° S, covering climatic conditions ranging from tropical to temperate/Arctic. We examined the influence of geospatial variables, current or historic climate variables, and additional local water physical and chemical variables measured for each site, as potential predictors of the incidence of ploidy state (diploidy, polyploidy, and mixed-cytotype) in the macrophyte species assemblage. At fine scales (individual sites), we observed the same latitudinal and climatic patterns influencing all macrophyte ploidy states, especially diploid species, compared to findings at a broad spatial resolution of 10° × 10° latitude-longitude. Ploidy state of macrophyte assemblages slightly, but significantly, differs between lentic and lotic environments. Along with geospatial and climate variables, local physical and chemical variables also helped predict the occurrence of polyploid and mixed-ploidy species. Our results support previous findings on ploidy state distribution and drivers at broader scales but also unravel new information on key drivers for the distribution of polyploid and mixed-ploidy species, relevant to understanding macrophyte adaptation mechanisms and evolutionary processes worldwide.