Extremely low genetic diversity of the northern limit populations of Nypa fruticans (Arecaceae) on Iriomote Island, Japan

The population genetic patterns of a species at its range limits have important implications for species conservation. Geographically marginal populations are expected to have lower genetic diversity and higher genetic differentiation than geographically central populations. Nypa fruticans is a mangrove palm which is widely distributed from tropical to subtropical zone of Southeast Asia and Oceania. For N. fruticans, Iriomote Island in Japan represents the most northern limit of the distribution of the species. We examined the genetic variation based on 11 microsatellite markers from all 137 known ramets of N. fruticans on Iriomote Island in comparison with the more central population. Adult ramets on Iriomote Island were composed entirely of one multilocus genotype in each population and had no genetic diversity within the populations. The formation of each population by vegetative propagation from only one immigrant individual was considered to be the method of reproduction. In addition, the new juvenile which were found on the opposite side of the island possessed different alleles from other ramets in the island. This indicates that the transfer of a new genotype from another location abroad can take place. The analyses provided useful information for the continued monitoring of the demography and genetic status of these populations.