Cytotype stability, facultative apomixis and geographical parthenogenesis in Ranunculus kuepferi (Ranunculaceae)

Abstract

Background and AimsAsexual organisms are more widespread in previously glaciated areas than their sexual relatives (‘geographical parthenogenesis’). In plants, this pattern is probably dependent on reproductive isolation and stability of cytotypes within their respective distribution areas. Both partial apomixis and introgressive hybridization potentially destabilize the spatial separation of sexual and apomictic populations. The wide distribution of apomicts may be further enhanced by uniparental reproduction which is advantageous for colonization. These factors are studied in the alpine species Ranunculus kuepferi.MethodsGeographical distribution, diversity and mode of reproduction of cytotypes were assessed using flow cytometry and flow cytometric seed screening on samples from 59 natural populations of Ranunculus kuepferi. Seed set of cytotypes was compared in the wild.Key ResultsDiploid sexuals are confined to the south-western parts of the Alps, while tetraploid apomicts dominate in previously glaciated and in geographically isolated areas despite a significantly lower fertility. Other cytotypes (3x, 5x and 6x) occur mainly in the sympatric zone, but without establishing populations. The tetraploids are predominantly apomictic, but also show a partial apomixis via an uncoupling of apomeiosis and parthenogenesis in the seed material. Both pseudogamy and autonomous endosperm formation are observed which may enhance uniparental reproduction.ConclusionsDiploids occupy a glacial relic area and resist introgression of apomixis, probably because of a significantly higher seed set. Among the polyploids, only apomictic tetraploids form stable populations; the other cytotypes arising from partial apomixis fail to establish, probably because of minority cytotype disadvantages. Tetraploid apomicts colonize previously devastated and also distant areas via long-distance dispersal, confirming Baker's law of an advantage of uniparental reproduction. It is concluded that stability of cytotypes and of modes of reproduction are important factors for establishing a pattern of geographical parthenogenesis.

Spontaneous hybrids between native and exotic Rubus in the Western United States produce offspring both by apomixis and by sexual recombination

“…However, the generation of F1 hybrids is expected to be a slow process in the case of R. ursinus  R. armeniacus, given that the flowering times of R. armeniacus and R. ursinus only overlap for a short period in California, and further north do not overlap at all (Susan Lambrecht, personal communication). Further, the possible occurrence of multiple hybrid cytotypes differing in ploidy level, which we could not assess but can result from the uncoupling of apomeiosis and parthenogenesis in facultative apomictic plants, may also be causing failed interploidal crosses and hybrid instability (Cosendai and Hörandl, 2010), impairing novel hybrids from spreading through sexual reproduction.…”

Distribution of bulbil‐ and seed‐producing plants of Poa alpina (Poaceae) and their growth and reproduction in common gardens suggest adaptation to different elevations

“…Four of eight analyzed mothers were able to perform meiosis, suggesting that the plants were facultative apomicts. In various taxa, populations of facultative apomicts have been found to consist of multiple genetically distinct clones ( Asker and Jerling, 1992 ), e.g., in Poa pratensis ( Matzk et al, 2005 ), Hypericum perforatum ( Barcaccia et al, 2006 ), Townsendia hookeri ( Thompson et al, 2008 ) and Ranunculus kuepferi ( Cosendai and Hörandl, 2010 ; see also Richards, 2003 ). Facultative apomixis could be an advantage because genotypes that are well adapted to current conditions could be exploited, while a certain level of genetic variation is still maintained for future adaptation ( Barcaccia et al, 2006 ).…”

Differential effects of polyploidy and diploidy on fitness of apomictic Boechera

“…In the Ranunculus auricomus complex, triploid apomictic plants produce fewer viable seeds and pollen than tetraploid and hexaploid apomicts (Izmaiłow 1996; although statistical error values for each measurement were not provided). Contrarily, Cosendai and Hörandl (2010) showed that pentaploid and hexaploid apomicts produce fewer viable seeds than tetraploids in Ranunculus kuepferi but found non-significant differences between triploids and tetraploids. These data point to ploidy as a source of fitness variation with direct influences on apomixis penetrance and stability in populations.…”