Genetic diversity, genetic differentiation and demographic history of Cryptomeria (Cupressaceae), a tertiary relict plant in East Asia based on RAD sequencing

Genetic structure and distribution patterns of modern floras are strongly affected by climatic change and geographical isolation. In the present study, we applied restriction site associated DNA sequencing (RAD-seq) to analyze the genetic structure and to simulate the demographic history of two extant Cryptomeria species in Japan (C. japonica) and Southeastern China (C. japonica var. sinensis). Thirteen natural populations representing the entire species distributed in East Asia were collected from Japan and China. At the species level, the genetic diversity of Cryptomeria was moderate (H-o = 0.217, H-e = 0.203) with a significant genetic differentiation among populations (85.30%, P < 0.001), especially between Japan and China lineages (F-ST = 0.147). Except for the Lushan (LS) population in China, all populations were clustered into two lineages (Japanese and Chinese), which was consistent with their geographical distribution. Approximate Bayesian computations (ABC) model indicated that the current two geographical lineages diverged from a common ancestral lineage, and that their divergence time was about 0.417 similar to 0.139 million years ago (Mya). Geographical isolation, climate change in the Quaternary, and human disturbance played important roles in genetic variation and distribution patterns of Cryptomeria in East Asia. Our results shed light on the speciation processes of Cryptomeria and provide a reference for the conservation of this species.