Origin and distribution of autopolyploids via apomixis in the alpine species Ranunculus kuepferi (Ranunculaceae)

Abstract

AbstractThe evolution of polyploids is strongly influenced by their mode of origin. Autopolyploidy is often hampered by disturbances of chromosome pairing and segregation at meiosis, while allopolyploids exhibit fewer meiotic problems and potentially have selective advantages because of hybridity. Apomixis, the asexual reproduction via seed in flowering plants, can overcome problems of meiotic reduction, favouring range expansions of polyploids. We elucidate the origin and genetic structure of apomictic cytotypes of the alpine species Ranunculus kuepferi by analyzing five microsatellite loci (SSRs) and Amplified Fragment Length Polymorphisms (AFLPs) on eight diploid and twelve polyploid populations from across the range of the species. Multiple allelism appears in three SSR loci in all polyploid cytotypes and is likely a result of facultative unbalanced meiotic events, as it is typical for autopolyploids. Low frequencies of private AFLP fragments (3%) and SSR alleles (4%) in tetraploids suggest that they evolved from diploid populations without the contribution of another divergent parental gene pool. A Neighbor‐joining tree of AFLPs revealed a low genetic divergence of cytotypes and at least three independent origins of tetraploid populations. Autopolyploidy is in R. kuepferi likely evolutionarily young and still has signatures of a facultative unbalanced meiosis. The shift to apomixis avoided consequences of meiotic problems and therefore enhanced rapid establishment of autotetraploids. The lack of hybridity in polyploids suggests that apomixis is successful even without genomic novelty. The distributional success of polyploid cytotypes is probably more due to the benefits of apomictic reproduction than to genetic consequences of polyploidization.