Phylogenetic relationships and arbuscular mycorrhizal diversity of Tolpis Adans. (Asteraceae), with special reference to island endemism and biogeography
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The plant genus Tolpis (Asteraceae) is a predominantly insular plant lineage. It inhabits four of the five archipelagoes that comprise the Atlantic region of Macaronesia and also occurs in Mediterranean Europe and North Africa. Twelve species are currently recognized in Tolpis, of which ten are insular and two continental. The majority of the insular species inhabit the five western Canarian islands, where they constitute endemics to specific ecological habitats. A comprehensive molecular phylogeny of Tolpis is generated via DNA sequences of one nuclear ribosomal and two low-copy nuclear DNA markers. Considerable phylogenetic uncertainty among inferred tree topologies is detected, and incongruence between these topologies is resolved via statistical hypotheses testing. The extant diversity of the genus is identified to be the result of two independent colonization pathways and adaptive radiations on several islands. Moreover, potential hybridization is detected between species that inhabit different islands and archipelagoes, indicating a more widespread historical distribution of the genus. Details of the biogeographic history of Tolpis are inferred via ancestral area reconstructions under parsimony and likelihood optimality criteria. The hypothesis that Tolpis may have undergone a back-dispersal from an island to a continental habitat is also tested. Uncertainty in taxon cladograms owing to the presence of hybrid or allopolyploid taxa is characterized and a potential adjustment strategy evaluated. Averaging reconstruction results over all optimal phylogenetic trees and the manual pruning of cloned DNA sequences are found potential adjustment strategies against the impact of topological uncertainty owning to hybrid or allopolyploid taxa. Adjusted ancestral area reconstructions in Tolpis do not support the scenario that the genus has undergone a reverse colonization of the continent. In addition to the phylogenetic and biogeographic history of the genus, the diversity of symbiotic mycorrhizal fungi associated with Tolpis is characterized. A molecular survey using two nuclear ribosomal DNA markers and 454 pyrosequencing is performed. Particular emphasis is placed on the quality filtering of resulting fungal DNA sequences, the generation of operational taxonomic units, and their taxonomic assignment via similarity searches against DNA sequence databases. Numerous potentially novel fungal genotypes are identified.