Intraspecific Karyotype Polymorphism and Chromosomal Evolution of Lysimachia mauritiana (Primulaceae) in the Ryukyu Archipelago of Japan and Taiwan

Here we discuss the cytogeographical patterns of cytotypes and the chromosomal evolution of Lysimachia mauritiana in the Ryukyus and Taiwan based on fluorescence in situ hybridization (FISH) analyses of 18 cytotypes using probes consisting of 5S and 45S rDNAs and telomere sequences. In the Ryukyus, the expansion of cytotypes was likely to have been influenced by maritime dispersal via the Kuroshio Current. The representative three cytotypes in Taiwan were also found in Japan: 20 (4m) TS was in the Daito Group; 20 (4m) TN characteristic of the northern Tokara Group was found within the Japanese mainland and named 20 (4m) JM; 18 (6m) Taiwan of the Sakishima Group was distinguished as 18 (6m) Ryukyu by FISH. Decreasing chromosome number was postulated as the result of the centric fusion of two pairs of t-chromosomes to a pair of m-chromosomes; 18 (6m) TF was formed from 20 (4m) TN in Taiwan, 16 (8m) from 18 (6m) Taiwan, Ryukyu, Satsunan, and 16 (6m) Satsunan from 18 (4m) Satsunan, respectively. Increasing chromosome number also occurred, by the centric fission of a pair of m-chromosomes to two pairs of t-chromosomes. 20 (4m) HD was formed from 18 (6m) Ryukyu. By centric fission of a pair of m-chromosomes to two pairs of t-chromosomes, and subsequent pericentric inversion of a pair of them to a pair of st-chromosomes, 20 (4m) MR was formed from 18 (6m) Satsunan. Karyotypic polymorphism among cyotypes has occurred by centric fusion/fission, pericentric inversion, deletion and reciprocal translocation in the Ryukyus and Taiwan.