Abstract
Changes in growth forms frequently accompany plant adaptive radiations, including páramo–a high‐elevation treeless habitat type of the northern Andes. We tested whether diverse group of Senecio inhabiting montane forests and páramo represented such growth form changes. We also investigated the role of Andean geography and environment in structuring genetic variation of this group. We sampled 108 populations and 28 species of Senecio (focusing on species from former genera Lasiocephalus and Culcitium) and analyzed their genetic relationships and patterns of intraspecific variation using DNA fingerprinting (AFLPs) and nuclear DNA sequences (ITS). We partitioned genetic variation into environmental and geographical components. ITS‐based phylogeny supported monophyly of a Lasiocephalus‐Culcitium clade. A grade of herbaceous alpine Senecio species subtended the Lasiocephalus‐Culcitium clade suggesting a change from the herbaceous to the woody growth form. Both ITS sequences and the AFLPs separated a group composed of the majority of páramo subshrubs from other group(s) comprising both forest and páramo species of various growth forms. These morphologically variable group(s) further split into clades encompassing both the páramo subshrubs and forest lianas, indicating independent switches among the growth forms and habitats. The finest AFLP genetic structure corresponded to morphologically delimited species except in two independent cases in which patterns of genetic variation instead reflected geography. Several morphologically variable species were genetically admixed, which suggests possible hybrid origins. Latitude and longitude accounted for 5%–8% of genetic variation in each of three AFLP groups, while the proportion of variation attributed to environment varied between 8% and 31% among them. A change from the herbaceous to the woody growth form is suggested for species of high‐elevation Andean Senecio. Independent switches between habitats and growth forms likely occurred within the group. Hybridization likely played an important role in species diversification.
Highlights
The uplift of Andean cordilleras played a major role in promoting diversification of the Neotropical flora (Antonelli, Nylander, Persson, & Sanmartin, 2009; Hoorn et al, 2010; Hughes, Pennington, & Antonelli, 2013)
In Aragoa Kunth (Plantaginaceae), another genus endemic to the northern Andes, arborescent plants of the montane forest evolved into páramo shrubs (Bello, Chase, Olmstead, Rønsted, & Albach, 2002; Fernández-Alonso, 1995), and growth form changes have been found in other Andean genera such as Lupinus L., Hinterhubera Sch
The results suggested that Senecio (Culcitium) nivalis (Kunth) Cuatrec. (Figure 1f) was closer to species of former Lasiocephalus than to other taxa of former Culcitium
Summary
The uplift of Andean cordilleras played a major role in promoting diversification of the Neotropical flora (Antonelli, Nylander, Persson, & Sanmartin, 2009; Hoorn et al, 2010; Hughes, Pennington, & Antonelli, 2013). In Aragoa Kunth (Plantaginaceae), another genus endemic to the northern Andes, arborescent plants of the montane forest evolved into páramo shrubs (Bello, Chase, Olmstead, Rønsted, & Albach, 2002; Fernández-Alonso, 1995), and growth form changes have been found in other Andean genera such as Lupinus L., Hinterhubera Sch. Bip. Our previous study of 13 Senecio species from the former Lasiocephalus, which all were diploid, based on nuclear DNA sequences (ITS region) and nuclear genome size data (Dušková et al, 2010), identified two major clades that largely correspond to the two habitat types, that is, montane forest and páramo. Based on extensive population sampling throughout the northern Andes and using an extended sample of ITS sequences complemented with highly variable AFLP (amplified fragment length polymorphism) markers, here we present deeper insights into the relationships among the Andean species of Senecio formerly classified in Lasiocephalus. We further examine patterns of genetic diversity within the group, and their correlation with environmental factors and Andean geography
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