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

Abstract

The 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.

Complex Geographical Distribution of Ploidy Levels inPolylepis australis(Rosaceae), an Endemic Tree Line Species in Argentina

“…Second, the extremely low frequencies of private AFLP bands found in the diploid northern Andean range (0.5%), the southern part of the Andean range (0%), and the southern populations of the Sierras de Cordoba (0.5%) in the study of Hensen et al (2011) indicate that there was no additional parental gene pool involved in the evolution of the tetraploids. Similarly low frequencies of private AFLP fragments have been reported for the autotetraploid Ranunculus kuepferi by Cosendai et al (2011). Thus, while other scenarios such as allopolyploid formation followed by long-distance dispersal or extinction of some parent populations are also conceivable, on current evidence we consider an autopolyploid origin to be more likely.…”

Correlations of polyploidy and apomixis with elevation and associated environmental gradients in an alpine plant

“…In sexual autopolyploids, profound difficulties may arise during chromosome segregation at meiosis due to the increased complexity of pairings among doubled and therefore identical chromosome sets, which mostly pair as multivalents. An efficient segregation of such multivalents in case of autotetraploid R. kuepferi remains difficult (Cosendai et al , 2011). Common segregation issues within enlarged chromosome sets can lead to disadvantageous irregularities such as aneuploidy (Birchler et al , 2007; Ozias-Akins and Van Dijk, 2007).…”

“…However, these studies did not quantify pathways of seed formation, and hence could not test for statistical correlations to geographical distances, elevation and related environmental parameters. Population genetic studies suggested autopolyploid origin (Cosendai et al , 2011), a high genotypic diversity and lack of geographical structure among tetraploids (Cosendai et al , 2013). Self-fertility of tetraploids supported the assumption of Baker’s law that rapid colonization could have played a role in distributions (Cosendai et al , 2013).…”

On the origin and evolution of apomixis in Boechera

“…Cosendai et al 2011). The diploids analyzed here contradict these findings: apomictic diploids are not purely the result of recurrent interspecific hybridization; however, triploid apomictic lineages may be recurrently derived from 2xApo-2xSex hybridization.…”