2023 年 74 巻 2 号 p. 55-70
To understand the diversity of Machilus (Lauraceae) in the Bonin Islands, we investigated genetic structure and several eco-geographical traits of 17 local populations, with using six nuclear microsatellite markers and observation of habitat differences and flowering phenology. As a results, we defined three groups in M. boninensis, two groups in M. kobu, and one group in M. pseudokobu. Populations of each species were genetically differentiated between Chichijima and Hahajima in the Bonin Islands. On Chichijima, populations of M. boninensis were further genetically differentiated between habitats, i.e., dry scrub and mesic forest. Within Chichijima and Hahajima populations, differences in sharp flowering peaks were observed among the groups; but populations of M. boninensis in mesic forests had a longer flowering period with multiple peaks. According to our observations, not only isolation by distance between the islands, but also ecological selection in response to dry scrub often formed on boninite soils, which result in similar physiological traits as in plants on serpentinite soils. This appears to drive diversification in Machilus in the Bonin Islands. The long flowering periods may have evolved as a successful adaptative to growing in the subcanopy layer or interior of the mesic forests.
