Geographical parthenogenesis and population genetic structure in the alpine species Ranunculus kuepferi (Ranunculaceae)

Abstract

Geographical parthenogenesis describes the enigmatic phenomenon that asexual organisms have larger distribution areas than their sexual relatives, especially in previously glaciated areas. Classical models suggest temporary advantages to asexuality in colonization scenarios because of uniparental reproduction and clonality. We analyzed population genetic structure and selffertility of the plant species Ranunculus kuepferi on 59 populations from the whole distribution area (European Alps, Apennines and Corsica). Amplified fragment length polymorphisms (AFLPs) and five microsatellite loci revealed individual genotypes for all populations and mostly insignificant differences between diploid sexuals and tetraploid apomicts in all measures of genetic diversity. Low frequencies of private AFLP fragments/simple sequence repeat alleles, and character incompatibility analyses suggest that facultative recombination explains best the unexpectedly high genotypic diversity of apomicts. STRUCTURE analyses using AFLPs revealed a higher number of partitions and a stronger geographical subdivision for diploids than for tetraploids, which contradicts expectations of standard gene flow models, but indicates a reduction of genetic structure in asexuals. Apomictic populations exhibited high admixture near the sexual area, but appeared rather uniform in remote areas. Bagging experiments and analyses of pollen tube growth confirmed self-fertility for pollen-dependent apomicts, but self-sterility for diploid sexuals. Facultative apomixis combines advantages of both modes of reproduction: uniparental reproduction allows for rapid colonization of remote areas, whereas facultative sexuality and polyploidy maintains genetic diversity within apomictic populations. The density dependence of outcrossing limits range expansions of sexual populations.

The population genetics of the fundamental cytotype-shift in invasive Centaurea stoebe s.l.: genetic diversity, genetic differentiation and small-scale genetic structure differ between cytotypes but not between ranges

“…Besides polyploidy, asexual propagation can help to avoid loss of genetic diversity during demographic bottlenecks (Cosendai et al 2013;Stein et al 2014). Moreover, there are species that became invasive despite exhibiting strong reductions of genetic diversity in the non-native range (reviewed in Uller and Leimu 2011).…”

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

“…Although Baker’s law explains well horizontal range expansions of apomictic plants (Baker, 1955, 1967; Mogie and Ford, 1988; Cosendai et al , 2013), it does not provide a theoretical background for the strong tendency of apomicts to colonize higher elevations and latitudes (Bierzychudek, 1985; Asker and Jerling, 1992). Alpine zones in high mountain systems represent extreme habitats for plant life, with lower temperatures including freezing, shorter vegetation periods and stronger wind exposure with increasing elevation (Nagy and Grabherr, 2009).…”

“…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).…”

Shading and litter mediate the effects of soil fertility on the performance of an understorey herb

“…We found distinct differences in the optimum conditions for abundance of clonal tubers, related to asexual reproduction, and flowering, indicative of plant investment in sexual reproduction. Trientalis tended to flower at higher rates in open environments, such as on low-fertility serpentine soils, which could increase the potential for gene flow between populations and formation of distinct genotypes in these conditions (Cosendai et al, 2013). Higher fruit set due to increased pollinator activity has been observed in open environments for a closely related species, Trientalis borealis (Anderson and Beare, 1983); a similar effect with T. latifolia would tend to further amplify the positive effect of open environments on sexual reproduction.…”