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Open Access Highly Accessed Research article

The explosive radiation of Cheirolophus (Asteraceae, Cardueae) in Macaronesia

Daniel Vitales1*, Teresa Garnatje2, Jaume Pellicer3, Joan Vallès1, Arnoldo Santos-Guerra4 and Isabel Sanmartín5*

Author Affiliations

1 Laboratori de Botànica – Unitat associada CSIC, Facultat de Farmàcia, Universitat de Barcelona, 08028 Barcelona, Catalonia, Spain

2 Institut Botànic de Barcelona (IBB-CSIC-ICUB), 08038 Barcelona, Catalonia, Spain

3 Jodrell Laboratory, Royal Botanic Gardens Kew, TW9 3DS Richmond, UK

4 Jardín de Aclimatación de la Orotava, 38400 Tenerife, Spain

5 Real Jardín Botánico (RJB-CSIC), 28014 Madrid, Spain

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BMC Evolutionary Biology 2014, 14:118  doi:10.1186/1471-2148-14-118

Published: 2 June 2014

Abstract

Background

Considered a biodiversity hotspot, the Canary Islands have been the key subjects of numerous evolutionary studies concerning a large variety of organisms. The genus Cheirolophus (Asteraceae) represents one of the largest plant radiations in the Canarian archipelago. In contrast, only a few species occur in the Mediterranean region, the putative ancestral area of the genus. Here, our main aim was to reconstruct the phylogenetic and biogeographic history of Cheirolophus with special focus on explaining the origin of the large Canarian radiation.

Results

We found significant incongruence in phylogenetic relationships between nuclear and plastid markers. Each dataset provided resolution at different levels in Cheirolophus: the nuclear markers resolved the backbone of the phylogeny while the plastid data provided better resolution within the Canarian clade. The origin of Cheirolophus was dated in the Mid-Late Miocene, followed by rapid diversification into the three main Mediterranean lineages and the Macaronesian clade. A decrease in diversification rates was inferred at the end of the Miocene, with a new increase in the Late Pliocene concurrent with the onset of the Mediterranean climate. Diversification within the Macaronesian clade started in the Early-Mid Pleistocene, with unusually high speciation rates giving rise to the extant insular diversity.

Conclusions

Climate-driven diversification likely explains the early evolutionary history of Cheirolophus in the Mediterranean region. It appears that the exceptionally high diversification rate in the Canarian clade was mainly driven by allopatric speciation (including intra- and interisland diversification). Several intrinsic (e.g. breeding system, polyploid origin, seed dispersal syndrome) and extrinsic (e.g. fragmented landscape, isolated habitats, climatic and geological changes) factors probably contributed to the progressive differentiation of populations resulting in numerous microendemisms. Finally, hybridization events and emerging ecological adaptation may have also reinforced the diversification process.

Keywords:
Allopatric speciation; Canary Islands; Diversification; Island radiation; Mediterranean Basin; Phylogeography