Abstract
The Amami Island group of the Ryukyu Archipelago, Japan, harbors extensive species diversity of Asarum in a small landmass. The fine-scale population genetic structure and diversity of nine insular endemic Asarum species were examined using nuclear DNA microsatellite loci and ITS sequences. High population genetic diversity (HS = 0.45–0.79) was estimated based on the microsatellites, implying outcrossing of Asarum species within populations accompanied by inbreeding. Bayesian clustering analyses revealed that species were divided into three robust genetic clusters and that the species within each cluster had a homogeneous genetic structure, indicating incomplete lineage sorting. This conclusion was supported by an ITS phylogeny. The degree of genetic differentiation among species was very low both within and between clusters (FST = 0.096–0.193, and 0.096–0.266, respectively). Although species can be crossed artificially to produce fertile hybrids, our results indicate that there is very little evidence of hybridization or introgression occurring among species in the wild, even within stands composed of multiple sympatric species. The highly differentiated floral morphology of the studied species is likely to impose reproductive isolation between them and maintain their integrity in the wild. A lack of genetic differentiation between sympatric species suggests that speciation within this group occurred rapidly and recently.
Highlights
The species richness of islands makes them suitable experimental systems for elucidating speciation mechanisms
In this study we examined the population genetic structure of the nine Asarum species that occur on the Amami-Oshima and Tokunoshima Islands in the Ryukyu Archipelago using nuclear DNA microsatellite loci
The nine Amami Group endemics were placed in a large polytomous clade that comprised insular endemics of the Ryukyu Islands, Taiwan, and mainland Japan (Clade A: 0.93 Bayesian posterior probabilities (BPP) in Bayesian inference (BI))
Summary
The species richness of islands makes them suitable experimental systems for elucidating speciation mechanisms. Traditional island biogeography studies [1, 2] have suggested that this richness is due mostly to the speciation of migrants within and among islands, and recent island phylogeography studies have corroborated this conclusion [3,4,5,6]. Tight species cohesion among sympatric insular wild gingers on continental islands. Environment, Japan to H.S. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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