Polyploid frequency decreases with elevation but increases with distance to glacial refugia in the Eastern European Alps

Polyploidy, the possession of more than two sets of chromosomes in somatic cells, is a major driver in the diversification of flowering plants. Whereas an association between the occurrence of polyploids and latitude suggests a major impact of temperature on their global distribution, it remains unknown how polyploid frequency varies at regional spatial scales, leaving unclear the overall robustness of such relationship and its major determinants. Here, we present a flora-wide dataset of newly sampled, georeferenced ploidy occurrence data for ca. 42,000 samples of angiosperms collected along 101 elevational transects across the Eastern European Alps. Based on these data, we find that on a regional level polyploid frequency decreases with elevation, in contrast to expectations derived from global latitudinal distribution patterns. Moreover, polyploid frequency increases with distance from glacial refugia for samples below the timberline, particularly for plants with limited dispersal abilities. These results suggest that range dynamics associated with Pleistocene climatic fluctuations rather than current temperature may have played a predominant role for the current distribution of polyploids in temperate mountain ranges. In sum, our systematic fine-scale survey identified a complex interplay between historical processes and current environments on polyploid distribution that have remained undetected at the global scale.