Center of origin and evolutionary history in the high Andean genus Oritrophium (Astereae, Asteraceae)

Abstract

Páramo, the most species-rich tropical mountain ecosystem, is relatively well-researched in terms of the diversity and evolutionary sources of its flora, yet we know very little about the diversification within this environment. This study aims to unravel the evolutionary history of Oritrophium, an endemic genus of alpine habitats in North and South America, with a disjunct and bi-modal distribution of its species diversity. We aim to disentangle the center of origin and radiation of the genus, and mechanisms structuring its genetic diversity at inter- and intra-specific level. We sampled 19 species (85% from the total) and extended the sampling at population level for the two widely distributed species, O. limnophilum and O. peruvianum, comprising 19 and 24 populations, respectively. Using nuclear ribosomal internal transcribed spacer (ITS) and trnL-trnF chloroplast DNA region, we reconstructed dated phylogenies to test the monophyly of the genus and unravel possible historical forces underlying its diversification. We also performed an ancestral area estimation to reconstruct the biogeographic history of the genus. At the population level, we constructed haplotype networks and run spatial analyses of molecular variance to explore possible mechanisms that operate on structuring the diversity at intraspecific level. Oritrophium resulted polyphyletic, with two species being closely related to Erigeron and three other species ambiguously related to Erigeron, Diplostephium, Linochilus, and/or Hinterhubera. The remaining 14 species formed a clade, Oritrophium s.s., that likely originated during the Early Pliocene in the Andes of northwestern Bolivia to southern Ecuador, the center of the genus' diversity. The group likely diversified with the emergence of the Páramo during the Late Pliocene and further dispersed mainly from South-to-North in the Pleistocene. This migration involved both, long-distance dispersal from the Central Andes to Mexico and gradual migration of the species along the Andes. Accordingly, Oritrophium s.s. appears as the first record of a long-distance dispersal from the Páramo of South America to North America. The dispersal pattern within South America was mirrored by the intraspecific population diversity and structure of the investigated species.