Biogeography of Coptis Salisb. (Ranunculales, Ranunculaceae, Coptidoideae), an Eastern Asian and North American genus

Abstract

Background: Numerous studies have favored dispersal (colonization) over vicariance (past fragmentation) events to explain eastern Asian-North American distribution patterns. In plants, however the disjunction between eastern Asia and western North America has been rarely examined using the integration of phylogenetic, molecular dating, and biogeographical methods. Meanwhile, the biogeographic patterns within eastern Asia remain poorly understood. The goldthread genus Coptis Salisb. includes 15 species disjunctly distributed in North America, Japan, mainland China, and Taiwan. We present a dated phylogeny for Coptis under the optimal clock model and infer its historical biogeography by comparing different biogeographic models.

Results: The split of Coptis and Xanthorhiza Marshall occurred in the middle Miocene (ca. 15.47 Ma). Coptis started their diversification in the early late Miocene (ca. 9.55 Ma). A late Miocene vicariance event resulted in the eastern Asian and western North American disjunction in the genus. Within eastern Asia, dispersals from mainland Asia to Japan and from Japan to Taiwan occurred at ca. 4.85 Ma and at ca. 1.34 Ma, respectively.

Conclusions: Our analyses provide evidence that both vicariance and dispersal events have played important roles in shaping the current distribution and endemism of Coptis, likely resulting from eustatic sea-level changes, mountain formation processes and an increasing drier and cooler climate from the middle Miocene onwards.

Keywords: Ancestral range evolution; Climate change; Coptis; Eastern Asian; Taiwan; Western North America.

Fig. 1

Geographic range of Coptis species. Doted lines in bold demarcate boundaries of the Holarctic and Paleotropical kingdoms according to Takhtajan [16]

Fig. 2

Dated phylogeny of Coptis inferred from the combined plastid and nuclear data using BEAST under the random clock model and birth-death tree prior. Gray bars represent 95% highest posterior density intervals. Nodes of interests were marked as 1–5 in bold. All nodes are strongly supported (PP > 0.95) except for one node (in dashed line). Plio., Pliocene; Plt., Pleistocene

Fig. 3

Ancestral range estimation (ARE) for Copits BEAST using BioGeoBEARS under the DIVALIKE model. Labeled nodes (1 to 5, as referred to Fig. 2), with 95% highest posterior densities (grey bars), are discussed in the text. The estimated ancestral ranges with the highest ML probability are shown by boxes on each node. Additional file 2: Figure S1 provides all ARE per node with pies. A pie is placed in this figure at the root with the highest probability less than 50%. The depictions of temperature (in red) and sea level (in black) changes are modified from Zachos et al. [45] and Haq et al. [57], respectively. Plio., Pliocene; Plt., Pleistocene