A shift in species niche through autopolyploidy: From sexual to vegetative reproduction in Saxifraga oppositifolia.

BACKGROUND AND AIMS: Polyploidy has been essential in the evolution of angiosperms, facilitating novel adaptations, enhancing speciation, and contributing to the establishment of larger evolutionary lineages. However, newly formed polyploids require sufficient niche differentiation to survive and coexist with the diploid ancestor. Polyploids are commonly reproductively challenged, which may lead to rapid development of asexual reproduction, which may, in turn, lead to reproductive barriers or ecological niche divergence. Through this study, we investigate whether autopolyploidization has induced a shift from sexual reproduction to vegetative propagation in the arctic-alpine Saxifraga oppositifolia (Saxifragaceae) and thus facilitated the establishment of polyploids in mixed-cytotype populations. METHODS: We sampled data on capsule- and seed production, seed germination, rooting ability, and leaf production among cytotypes through a combination of growth chamber experiments and in-situ observations in a field setup across different habitats (ridges, slopes, and riverbeds) in Svalbard including > 700 georeferenced S. oppositifolia plants with known cytotype (diploid, triploid, or tetraploid). Through hypothesis testing and an explorative model search for relevant covariates (e.g., growth form, habitat, soil type), we tested the effect of cytotype on sexual and vegetative reproductive outcomes. KEY RESULTS: Polyploids had lower sexual reproductive investment (i.e., capsule production and seed production) and higher vegetative investment (i.e., leaf production and rooting ability), showing that polyploidy significantly has affected both sexual reproduction and vegetative propagation. CONCLUSIONS: Our findings confirm a shift in reproductive strategy towards less sexual investment and enhanced vegetative investment in triploid and tetraploid individuals. This shift may enhance polyploid survival in habitats with shorter growing season and limited pollinator availability, and thus explains their higher frequency in such habitats. These results support autopolyploidy as an evolutionary mechanism that may allow Arctic species to adapt to ongoing, rapid changes.