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

Abstract

BackgroundConsidered 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.ResultsWe 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.ConclusionsClimate-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.

Bayesian spatio‐temporal reconstruction reveals rapid diversification and Pleistocene range expansion in the widespread columnar cactus Pilosocereus

“…(Silva et al., ) and the Pilosocereus aurisetus species complex (Bonatelli et al., ) are probably upwardly biased due to the use of distant fossil calibrations and improper tree priors when there is ongoing gene flow (Ho et al., ). If our age estimates are right, species divergence was rapid with a net diversification rate resembling those exhibited by some island radiations (Vitales et al., ). This might explain the weak support for internal nodes recovered in our study (Figure ) and in other infrageneric studies of cacti (Bonatelli et al., ; Franco et al., ).…”

Pleistocene extinctions as drivers of biogeographical patterns on the easternmost Canary Islands

“…time constraints for recolonization) could explain why outstanding examples of island colonization and diversification, such as Cheirolophus (17 endemic species) or Pericallis (12), have no extant representatives on these islands, despite potential availability of suitable habitats (e.g. Vitales et al., ). In turn, recent episodes of ECI colonization (second pattern; Figure b; Table ) imply earlier extirpation, and would account for the limited ECI representation (one or two closely related species) of lineages with similar high colonization abilities (e.g.…”

Palaeo‐islands as refugia and sources of genetic diversity within volcanic archipelagos: the case of the widespread endemic Canarina canariensis (Campanulaceae)

“…; Vitales et al . ,b). Nevertheless, the complex topographies and long histories of avalanches and secondary eruptions of many of these islands are likely to have favoured within‐island diversification (Juan et al .…”