Abstract
Mountain uplifts have generated new ecologic opportunities for plants, and triggered evolutionary processes, favouring an increase on the speciation rate in all continents. Moreover, mountain ranges may act as corridors or barriers for plant lineages and populations. In South America a high rate of diversification has been linked to Andean orogeny during Pliocene/Miocene. More recently, Pleistocene glacial cycles have also shaped species distribution and demography. The endemic genus Escallonia is known to have diversified in the Andes. Species with similar morphology obscure species delimitation and plants with intermediate characters occur naturally. The aim of this study is to characterize genetic variation and structure of two widespread species of Escallonia: E. alpina and E. rubra We analyzed the genetic variation of populations of the entire distribution range of the species and we also included those with intermediate morphological characters; a total of 94 accessions from 14 populations were used for the Amplified Fragment Length Polymorphism (AFLP) analysis. Plastid DNA sequences (trnS-trnG, 3'trnV-ndhC intergenic spacers and the ndhF gene) from sixteen accessions of Escallonia species were used to construct a Statistical Parsimony network. Additionally, we performed a geometric morphometrics analysis on 88 leaves from 35 individuals of the two E. alpina varieties to further study their differences. Wright's Fst and analysis of molecular variance tests performed on AFLP data showed a significant level of genetic structure at the species and population levels. Intermediate morphology populations showed a mixed genetic contribution from E. alpina var. alpina and E. rubra both in the Principal Coordinates Analysis (PCoA) and STRUCTURE. On the other hand, E. rubra and the two varieties of E. alpina are well differentiated and assigned to different genetic clusters. Moreover, the Statistical Parsimony network showed a high degree of divergence between the varieties of E. alpina: var. alpina is more closely related to E. rubra and other species than to its own counterpart E. alpina var. carmelitana Geometric morphometrics analysis (Elliptic Fourier descriptors) revealed significant differences in leaf shape between varieties. We found that diversity in Escallonia species analyzed here is geographically structured and deep divergence between varieties of E. alpina could be associated to ancient evolutionary events like orogeny. Admixture in southern populations could be the result of hybridization at the margins of the parental species' distribution range.
Highlights
Mountain orogeny has been a major factor in plant evolution in all continents, and has been linked to recent diversification and speciation events (Hughes and Atchison 2015)
In the network (Fig. 3), one major group is composed of E. leucantha, E. illinita, E. rosea, E. revoluta, E. myrtoidea, E. alpina, E. rubra, and E. florida, which are separated by few mutational steps
New sequences of E. alpina var. alpina and var. carmelitana were included in the major group together with those downloaded from the GenBank database
Summary
Mountain orogeny has been a major factor in plant evolution in all continents, and has been linked to recent diversification and speciation events (Hughes and Atchison 2015). The Andes themselves could have played as a North-South corridor allowing the exchange of plant lineages; or as a barrier promoting vicariance. These evolutionary processes triggered by the Andean uplift promoted a high speciation rate conducting to great biological diversity in South America (Antonelli et al 2009; Hartley 2003; Kier et al 2009; Luebert et al 2011; Ortiz-Jaureguizar and Cladera 2006; Scherson et al 2008).
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