Abstract
Aim The genus Camellia is widely distributed, primarily
in East Asia. Camellia japonica is located at the northern limit
of this genus distribution, and elucidating its distribution changes is
crucial for understanding the evolution of plants in this region, as
well as their relationship with geological history and climate change.
Also, the classification of sect. Camellia in Japan has not been
clarified. Therefore, the aim of this study is to understand the
evolutionary history of Japanese sect. Camellia.
Location Japan, Korea, Taiwan, and the coastal area of China
Taxon Camella (Theaceae). Methods The genetic
population structure was analyzed by SNP data using MIG-seq. The
relationship between Japanese sect. Camellia including the
related species in China was further inferred from the phylogeny
generated by RA x ML, SplitsTree and PCA. Population genetic structure
was inferred using a Bayesian clustering method (ADMIXTURE). We then
employed approximate Bayesian computation to explore the changes in
population, asking which events best explain the phylogeographical
signature. Ecological niche modeling was combined with genetic analyses
to compare current and past distributions. Results The analyses
consistently showed that C. japonica and C. rusticana are
distinct, having diverged from each other between approximately 5.4 and
12 million years ago. Furthermore, C. japonica differentiated
into four major populations (North, South, Ryukyu-Taiwan, and
Continent). Main Conclusion Japanese sect. Camellia
underwent speciation during archipelago formation, reflecting its
ancient evolutionary history compared with other native Japanese plants.
The conventional hypothesis that C. rusticana diverged from
C. japonica in snow-rich environments under Quaternary period was
rejected. Our results suggest that both species have been independent
since ancient times, and that ancestral populations of C.
japonica have persisted in northern regions. Furthermore, it is
estimated that C. japonica population on the continent
experienced a back-dispersal event from southern Japan during the late
Pleistocene glaciation.