Tani Naoki, Yoshimaru Hiroshi, Kawahara Takayuki, Hoshi Yoshio, Nobushima Fuyuo, Yasui Takaya
Department of Forest Genetics, Forestry and Forest Products Research Institute, Matsunosato, Tsukuba, Ibaraki 305-8687 Japan.
BMC Ecol. 2006 Oct 11;6:14. doi: 10.1186/1472-6785-6-14.
Morus boninensis, is an endemic plant of the Bonin (Ogasawara) Islands of Japan and is categorized as "critically endangered" in the Japanese red data book. However, little information is available about its ecological, evolutionary and genetic status, despite the urgent need for guidelines for the conservation of the species. Therefore, we adopted Moritz's MU concept, based on the species' current genetic structure, to define management units and to select mother tree candidates for seed orchards.
Nearly all individuals of the species were genotyped on the basis of seven microsatellite markers. Genetic diversity levels in putative natural populations were higher than in putative man-made populations with the exception of those on Otouto-jima Island. This is because a limited number of maternal trees are likely to have been used for seed collection to establish the man-made populations. A model-based clustering analysis clearly distinguished individuals into nine clusters, with a large difference in genetic composition between the population on Otouto-jima Island, the putative natural populations and the putative man-made populations. The Otouto-jima population appeared to be genetically differentiated from the others; a finding that was also supported by pairwise FST and RST analysis. Although multiple clusters were detected in the putative man-made populations, the pattern of genetic diversity was monotonous in comparison to the natural populations.
The genotyping by microsatellite markers revealed strong genetic structures. Typically, artificial propagation of this species has ignored the genetic structure, relying only on seeds from Otouto-jima for replanting on other islands, because of a problem with inter-specific hybridization on Chichi-jima and Haha-jima Islands. However, this study demonstrates that we should be taking into consideration the genetic structure of the species when designing a propagation program for the conservation of this species.
小笠原桑是日本小笠原（小笠原）群岛的特有植物，在日本《红色名录》中被列为“极度濒危”物种。然而，尽管迫切需要该物种的保护指南，但关于其生态、进化和遗传状况的信息却很少。因此，我们采用了基于该物种当前遗传结构的莫里茨的MU概念，来定义管理单元并为种子园选择母树候选者。
几乎所有该物种个体都基于7个微卫星标记进行了基因分型。除小御所岛的种群外，假定自然种群的遗传多样性水平高于假定人工种群。这是因为建立人工种群时可能仅使用了有限数量的母树来采集种子。基于模型的聚类分析清楚地将个体分为9个簇，小御所岛的种群、假定自然种群和假定人工种群之间的遗传组成差异很大。小御所岛的种群似乎在基因上与其他种群有所分化；成对FST和RST分析也支持了这一发现。尽管在假定人工种群中检测到多个簇，但与自然种群相比，遗传多样性模式较为单一。
微卫星标记基因分型揭示了强大的遗传结构。通常，由于父岛和母岛存在种间杂交问题，该物种的人工繁殖忽略了遗传结构，仅依靠小御所岛的种子在其他岛屿重新种植。然而，本研究表明，在设计该物种的保护繁殖计划时，我们应该考虑其遗传结构。
