Do floral and niche shifts favour the establishment and persistence of newly arisen polyploids? A case study in an Alpine primrose.

Background and Aims Polyploidization plays a key role in plant evolution. Despite the generally accepted ‘minority-cytotype exclusion’ theory, the specific mechanisms leading to successful establishment and persistence of new polyploids remain controversial. The majority of newly arisen polyploids are expected to quickly disappear, because they are less common, have fewer potential mates, or may not be able to successfully compete with co-occurring progenitors at lower ploidy levels. Changes in floral traits and ecological niches have been proposed as important mechanisms to overcome this initial frequency-dependent disadvantage. We aimed at determining whether dodecaploids of the heterostylous P. marginata differ from their hexaploid progenitors in P. marginata and P. allionii for selected floral traits and ecological preferences that might be involved in establishment and persistence, providing a possible explanation for the origin of polyploidized populations. Methods We quantified and compared floral morphological traits and ecological niche preferences among dodecaploids and their hexaploid progenitors in P. marginata and P. allionii, all restricted to the southwestern Alps. Key Results We detected differences in floral traits between dodecaploids and their closest relatives, but such differences seem too weak to counter the strength of minority cytotype disadvantage and are unlikely to enable the co-existence of different cytotypes. Furthermore, our results suggest no transition to selfing and preservation of full distyly in dodecaploids. Finally, dodecaploids occurred almost exclusively in environments that were predicted to be suitable also for their closest hexaploid relatives. Conclusions In light of our results, P. marginata dodecaploids have probably been able to establish and persist by occupying geographical areas not yet filled by their closest relatives without significant evolution in their climatic and pollination niches. Dispersal limitation and minority-cytotype exclusion probably maintain their current range disjunct from those of its close relatives.