Abstract
The Andes are an important biogeographic region in South America extending for about 8000 km from Venezuela to Argentina. They are – along with the Patagonian steppes – the main distribution area of ca. 18 polyploid species of Silene sect. Physolychnis. Using nuclear ITS and plastid psbE-petG and matK sequences, flow cytometric ploidy level estimations and chromosome counts, and including 13 South American species, we explored the origin and diversification of this group. Our data suggest a single, late Pliocene or early Pleistocene migration of the North American S. verecunda lineage to South America, which was followed by dispersal and diversification of this tetraploid lineage in the Andes, other Argentinian mountain ranges and the Patagonian steppes. Later in the Pleistocene South American populations hybridized with the S. uralensis lineage, which led to allopolyploidisation and origin of decaploid S. chilensis and S. echegarayi occurring at high elevations. Additionally, we show that the morphological differentiation in leaf shape correlated with divergent habitats (high elevation Andes vs. lower elevation Patagonian steppes) is also supported phylogenetically, especially in the ITS tree. Lastly, the species boundaries among the narrow-leaved Patagonian steppe species are poorly resolved and need more thorough taxonomic revision.
Highlights
Polyploidy has significantly contributed to the diversification and radiation of flowering plants (Soltis et al, 2009, 2016; Wood et al, 2009; Husband et al, 2013; Madlung, 2013) and at least two polyploidisation rounds have occurred in all angiosperms (Jiao et al, 2011)
The karyotypes cannot be directly compared without additional markers, as it is impossible to define homo- or homeologous chromosome pairs based on chromosome morphology alone, especially given their very similar sizes and types
Many Northern American temperate plant lineages have colonized the South American Andes after overland connections were established between the two continents, but the timing of migrations differed among the groups (Bell and Donoghue, 2005; FIGURE 6 | Bayesian consensus chronograms (Maximum Clade Credibility trees) showing the temporal diversification of South American Silene sect
Summary
Polyploidy has significantly contributed to the diversification and radiation of flowering plants (Soltis et al, 2009, 2016; Wood et al, 2009; Husband et al, 2013; Madlung, 2013) and at least two polyploidisation rounds have occurred in all angiosperms (Jiao et al, 2011). Diversification of South American Silene polyploids have been suggested to have lower speciation and higher extinction rates than diploids (Mayrose et al, 2011). In North America most native species are tetraploids or octoploids (Popp and Oxelman, 2007), whereas little is known about the role of polyploidisation in the evolution of South American Silene sect. The section includes species with upright stems, irregular thyrsoid inflorescences and mostly small, often dissected petal limbs (Petri and Oxelman, 2011). It was most thoroughly studied by Bocquet (1969), but based on molecular studies (e.g., Popp et al, 2005; Popp and Oxelman, 2007; Jenkins and Keller, 2010; Rautenberg et al, 2010; Petri and Oxelman, 2011) additional species were included in the section, establishing a morphologically rather diverse but phylogenetically well-supported monophyletic group (Petri and Oxelman, 2011)
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