Allozyme variation of populations of Castanopsis carlesii (Fagaceae) revealing the diversity centres and areas of the greatest divergence in Taiwan

Abstract

Background and aims: The genetic variation and divergence estimated by allozyme analysis were used to reveal the evolutionary history of Castanopsis carlesii in Taiwan. Two major questions were discussed concerning evolutionary issues: where are the diversity centres, and where are the most genetically divergent sites in Taiwan?

Methods: Twenty-two populations of C. carlesii were sampled throughout Taiwan. Starch gel electrophoresis was used to assay allozyme variation. Genetic parameters and mean FST values of each population were analysed using the BIOSYS-2 program. Mean F(ST) values of each population against the remaining populations, considered as genetic divergence, were estimated using the FSTAT program.

Key results: Average values of genetic parameters describing the within-population variation, the average number of alleles per locus (A=2.5), the effective number of alleles per locus (Ae=1.38), the allelic richness (Ar=2.38), the percentage of polymorphic loci (P=69%), and the expected heterozygosity (He=0.270) were estimated. High levels of genetic diversity were found for C. carlesii compared with other local plant species. Genetic differentiation between populations was generally low.

Conclusions: From the data of expected heterozygosity, one major diversity centre was situated in central Taiwan corroborating previous reports for other plant species. According to the mean FST value of each population, the most divergent populations were situated in two places. One includes populations located in north central Taiwan between 24.80 degrees N and 24.20 degrees N. The other is located in south-eastern Taiwan between 22.40 degrees N and 23.10 degrees N. These two regions are approximately convergent with the most divergent locations determined for several other plant species using chloroplast DNA markers published previously. An important finding obtained from this study is that unordered markers like allozymes can be used to infer past population histories as well as chloroplast DNA markers do.

Fig. 1.

Map of Taiwan and sampling sites of Castanopsis carlesii in this study. Stars indicate areas with higher genetic diversity (LH, 0·398; KL, 0·361). Dotted lines indicate the regions with high genetic divergence. Open circles indicate populations with higher values of genetic divergence (HK, 0·108; TW, 0·093; TN, 0·077; FS, 0·102; TA, 0·089; AM, 0·086; KW, 0·067), closed circles indicate the remaining populations. CMR, Central Mountain Range; HR, Hsuehshan Range.

Fig. 2.

Relationships of expected heterozygosity (H_e) and mean F_ST with latitude: (A) H_e of each population in this study; (B) mean F_ST of each population. Closed circles indicate western populations, and open circles indicate eastern populations.

Fig. 3.

Two-dimensional representation of the principal component analysis (PCA) of the genetic relationships among 22 populations (indicated as a two-letter code) of Castanopsis carlesii, inferred from the frequencies of 40 alleles. The symbols of filled circles and triangles indicated populations on the western and eastern sides of the CMR, respectively. The percentages of the total variability explained by the two first components were 28·5 % for axis 1 and 19·1 % for axis 2.