Systematic study on the process of speciation, infra-specific differentiation and genomic differentiation of higher plants on the island system with special reference to the Ryukyu Archipelago

琉球群岛是上新世至第四纪陆桥多次海进海退形成和分割的产物。为了揭示分布格局和专业化程度，我们研究了种内的细胞器DNA的核苷酸序列的多样性，在珍珠菜mauritiana（报春花科）。两个间隔区的序列区分了琉球群岛、九州和日本本州的四种主要单倍型。4种单倍型的分布范围与地理分界线、琉球群岛的庆良间缺口和吐噶喇缺口、太平洋一侧和日本海一侧相吻合。这两个构造空区被认为是更新世期间连接中国大陆、台湾和九州的陆桥的主要地理空区。我们还检查了体细胞染色体数目和形态。琉球南部和中部的染色体数目主要为2n=18，有6条大型中部着丝点染色体，而台湾和冲绳的染色体数目主要为2n=20，2n=17来自冲绳。2n=16。也被报道。另一方面，北方琉球群岛只包括2n=20与四个大的中部着丝点染色体。cpDNA单倍型和染色体数目之间没有任何相关性。

The Ryukyu Archipelago is the product of the repeated formation and division of a landbridge by means of transgression and regression during the Pliocene and Quaternary periods. To reveal the distribution pattern and the degree of specialization, we examined the intraspecific diversification of nucleotide sequences of organelle DNA in Lysimachia mauritiana (Primulaceae). The sequences of two spacer regions distinguish four major haplotypes on the Ryukyu Archipelago, Kyushu and Honshu of Japan. The distribution range of the four haplotypes is well concordant with the geographical boundaries, Kerama and Tokara Gaps on the Ryukyu Islands, the Pacific Ocean side and the Sea of Japan side. The two tectonic gaps have been recognized to be major geographic gaps of the landbridge through the mainland of China, and Taiwan and Kyushu during the Pleistocene. We also examined the somatic chromosome numbers and morphology. The chromosome number from the southern and middle Ryukyu was mainly 2n=18 with six large metacentric chromosomes while 2n=20 from Taiwan and Okinawa Isl., 2n=17 from Okinawa Isl. and 2n=16 from Amamioshima Isl. were also reported. On the other hand, islands of Northern Ryukyu exclusively comprise 2n=20 with four large metacentric chromosomes. Any correlation between cpDNA haplotypes and chromosome numbers was not recognized.