Low Genetic Diversity of Cycas taitungensis (Cycadaceae), an Endemic Species in Taiwan, Revealed by Allozyme Analysis

Abstract

The purpose of this study was to investigate the population genetic structure of Cycas taitungensis C. F. Shen, K. D. Hill, C. H. Tsou & C. J. Chen using isozyme techniques. Only 2 isolated populations of C taitungensis were found in the southeastern part of Taiwan. Nineteen enzyme systems examined were encoded by 40 putative loci. All loci were monomorphic with the exception of Mdh-2, which was resolved into 3 alleles. The mean number of alleles per locus of these 2 populations, Luyei River and Coastal Range, was 1.08 vs. 1.05, with an average of 1.07. The mean effective number of alleles was considerably low, averaging 1.01 for both populations. The mean percentage of polymorphic loci and average value were both 2.5%. Mean heterozygosity was 0.014 for Luyei River and 0.011 for Coastal Range, with an average of 0.013. In conclusion, C taitungensis exhibits extremely low levels of genetic diversity. Wright's F-statistics showed negative values. The x^2 analyses revealed that the observed distribution of genotypes for Mdh-2 within population was in Hardy-Weinberg equilibrium. In terms of genetic differentiation among populations, the F1 value was 0.034; thus more than 96% of the genetic diversity resided within a population, and the genetic differentiation between populations was low.