Recent origin and adaptive diversification of Ainsliaea (Asteraceae) in the Ryukyu Islands: molecular phylogenetic inference using nuclear microsatellite markers
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We investigated the phylogeny and phylogeography of four closely related Ainsliaea species (Asteraceae) on the continental Ryukyu Islands of eastern Asia, which consist of two flood-adapted “rheophyte” and two non-rheophyte (inland) species, based on 12 nuclear microsatellite loci. Phylogenetic analyses using 420 individuals from 26 populations showed that rheophytic A. linearis and A. oblonga are genetically distinct. Each species was clustered with the inland species that occur on the same islands, suggesting a different ancestry for the two rheophytes that evolved independently by local adaptation to flooded habitats. The results from the neighbor-joining clustering and principal coordinate analysis (PCoA) indicate that the southern populations of A. macroclinidioides are distinct lineages and ancestral to the northern populations as well as the other diverse species complex in the Ryukyus. These results suggest a pattern of colonization initially from the Asian mainland to the southern islands, followed by the northern islands via land bridges generated during the Quaternary glaciations. After isolation from southern populations, species radiation and regional differentiation within the northern clade occurred possibly via local adaptation and/or geographic isolation of the subdivided island bridge.