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• 收稿日期:2021-02-18 接受日期:2021-04-24

### Two species of the Rhodiola yunnanensis species complex distributed around the Sichuan Basin of China: Speciation in a ring?

Zi-Meng Wang, Shi-Yong Meng and Guang-Yuan Rao*

1. School of Life Sciences, Peking University, Beijing 100871, China
• Received:2021-02-18 Accepted:2021-04-24

Abstract: A ring species consists of two reproductively isolated forms connected by a chain of intergrading populations encircling a geographic barrier. The mountains encircling the Sichuan Basin in southwestern China harbor great species diversity and endemism, and they are candidate regions for ring species. Here, we examined a potential ring species complex with a ring distribution surrounding the Sichuan Basin and the reproductive barrier between sibling species Rhodiola yunnanensis and R. henryi of the R. yunnanensis complex. In this study, we test the hypothesis that R. yunnanensis and R. henryi diverged by the ring-species model using an amplicon sequencing strategy targeting the introns of 27 single-copy nuclear genes and 14 chloroplast DNA sequences. Our studies indicated that the R. yunnanensis complex is monophyletic, originates at the late Miocene, and forms its current ring distribution pattern after the LIG. In addition, clear genetic intergradation was not found among R. henryi populations within the distribution ring. All these findings suggest that the divergence of two sibling species was not driven by the geographic isolation, and they were not originated from the ring-species model; however, the basin-surrounding distribution pattern and reproductive barrier between them meet some criteria for being a ring species.