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Abstract
The genetic diversity of the mangrove tree species Kandelia candel and Bruguiera gymnorrhiza in the Southwest Islands of Japan was investigated. These islands are located at the periphery of the distribution area of the two species, and their populations are relatively small. Allozyme analyses of 17 loci in K. candel and 13 loci in B. gynmorrhiza revealed very little genetic variation in both species. At the species level, the proportion of polymorphic loci was 4.2%, the average effective number of alleles per locus was 1.02, and the average expected heterozygosity was 0.012 in K. candel. The corresponding figures for B. gymnorrhiza were 9.0%, 1.06 and 0.035, respectively. However, the coefficients of genetic differentiation among the populations were high (GST=0.165 for K. candel and 0.253 for B. gymnorrhiza). The genetic variation and habitat area of K. candel on Amami Island is greater than on the islands Okinawa and Iriomote. The genetic variation and habitat area of B. gymnorrhiza is greater on Iriomote Island than on the islands Okinawa and Amami. The level of genetic variation in both of the species might be related to their population sizes.