Population genetic analyses of two species of Distylium: D. racemosum growing in East Asian evergreen broad-leaved forests, and D. lepidotum endemic to the Ogasawara (Bonin) Islands

In this project, we analyzed the genetic variation of two related species of Hamamelidaceae, Distylium racemosum and D. lepidotum, living in different habitats and possessing distinctive morphological characteristics. Distylium racemosum is one of the dominant trees of broad-leaf evergreen forests in Japan, and D. lepidotum is a dominant shrub in dry scrub endemic to the Ogasawara Islands. We analyzed the nucleotide variation at 112 protein-coding loci in 95 samples for the two Distylium species, and inferred population structure and demographic history on the basis of these data. Our results showed that the samples from two Distylium species were genetically clustered into the following three groups: D. racemosum, D. lepidotum in the Chichijima Island, and D. lepidotum in the Hahajima Island. Furthermore, D. racemosum appears to have diverged first approximately 10 million years ago (MYA), and, then, the split of two populations of D. lepidotum occurred around 1MYA. Additionally, we detected a few candidate loci that may contribute to adaptation of the species or local populations by exploring the pattern of the variation within and between species using the FST-outlier approach.