Abstract
BACKGROUND: In East Asia, the evolutionary histories of Tertiary relicts are complex, involving not only southward retreats during the middle and late Tertiary but also repeated migrations northward or southward during the Quaternary. Three possible scenarios are hypothesized: High-Latitude Origin, Low-Latitude Origin, and Vicariance Origin. The phylogeography of Lindera obtusiloba is investigated using 27 independent nuclear low-copy genes to test these scenarios and explore key diversification processes. RESULTS: The genetic diversity and effective population size at low latitudes were approximately two/three times greater than those at high latitudes. A sharp genetic discontinuity with reciprocal monophyletic lineages and limited gene flow that diverged during the middle Pleistocene was revealed between high and low latitudes. The ancestral population was small, and demographic expansions occurred in both regions during the last interglacial period. Both High- and Low-Latitude Origin scenarios were supported by approximate Bayesian computation (ABC) modeling. Ancestral area reconstruction supported the Vicariance Origin scenario. Climate analysis revealed that populations in different regions had different climatic niches and isolation by environment existed, indicating potential ecological adaptation. Ecological niche modeling indicated bidirectional expansion at present, whereas only expansion to low latitudes from high latitudes was observed in the past. Two subclusters were further revealed in both regions. Eastward and postglacial westward migrations were detected at high and low latitudes, respectively. CONCLUSIONS: The evolution of East Asian Tertiary relict species is complex, as none of the three proposed scenarios are fully supported, and the diversification within each region differs for L. obtusiloba. Dual refugia in high and low latitudes offer long-term survival, and populations at high latitudes may develop ecological adaptations. Genomic data with richer genetic information and adaptation loci are likely to help elucidate the origin and adaptation history of East Asian Tertiary relicts in the future.