| Parashorea chinensis and Vatica guangxiensis, two endangered Dipterocarps narrowly ranged on the north edge of Tropical Asia, are now subjected to special protection in natural reserve and ex situ conservation programme. In the present study, the genetic diversity and population genetic structure of the natural populations and conserved populations of these two species were investigated using RAPD technique. The main results are highlighted in the following: 1. For three remaining natural populations and one ex situ cultivated population of V. guangxiensis, with 20 random primers, 231 loci were generated with 53.68% being polymorphic (PPB). The observed number of alleles (na) was 1.5368, the effective number of alleles (ne) was 1.2878, and Nei's gene diversity (h) was 0.1686. The level of genetic diversity within populations was low. The variation within populations was 55.09%, and 44.91% among populations (AMOVA); The GST was 0.3746 (POPGENE), indicating high level of genetic differentiation among populations. The result implies the conservation strategies of this endangered plant. Because of the low level of genetic diversity and high level of population differentiation, promoting gene flow (via seed and seedling) among populations would be a practical effort of conservation. 2. The amount of genetic diversity and RAPD bands were compared between natural populations (NS, NP, NX) and cultivated population (ML) to assess the efficiency of ex situ genetic conservation of V. guangxiensis. The population ML contained an intermediate genetic variation, with 30.74% bands being polymorphic. Of the total 231 bands generated in V. guangxiensis, 204 bands were also detected in population ML, indicating that 88.31% of the total genetic variations of this species were conserved in ex situ population. If only the alleles with moderate to high frequency (P>0.05) were considered, 204 out of 209 bands (97.61%) occurred in ex situ population ML. RAPD analysis also detected some exclusive bands in natural population NS(1) and population NP(5), while none of these exclusive bands were detected in ex situ conserved population ML. Our conclusions are that the ex situ conserved population ML contains representative genetic variation to maintain long-term survival and evolutionary process of V. guangxiensis, and that more extensive ex situ sampling in natural population NS and NP is needed to conserve more exclusive alleles in ex situ population. 3. 194 individuals in seven natural populations of P. chinensis were amplified with 20 random primers. 48.22% of RAPD loci were polymorphic across the whole species, while only 20.84% on average on population levels. Mean population gene diversity within populations (measured by Shannon's index of phenotypic diversity) was 0.7870, and total was 1.4100 for the whole species. 55.82% of the total gene diversity were distributed within populations, and 44.18% were among populations. Mean GST value arcoss loci was 0.4448. AMOVA analysis revealed 37.67% of the total genetic variation were attributed among regions, 11.40% among populations within regions, and 50.93% within populations. These results suggested low levels of genetic diversity in this species and strong regional population differentiation, which might be the results of population bottleneck resulting from the repeated extinction and recolonization in its evolutionary history. The implications of these results to conservation strategies of this endangered species were also discussed. 4. The spatial and temporal distribution patterns of population genetic structure of P. chinensis were investigated by using RAPD markers in three populations. Spatial distribution of individuals was also evaluated to obtain an insight into spatial relationships between individuals and genotypes. Morisita's index of dispersion (Iδ) revealed a random distribution of P. chinensis individuals in three studiedpopulations. Genetic diversity kept continuously decreasing from young group to old group in five groups rearranged from three studied populations according to individual age, and 64% low-frequency of RAPD bands (p≤0.05) occurring in young group were not detected in older group, and two possible explanations for this decreasing of genetic diversity were genetic drift in small population, or the effects of natural selection on the alleles which had closed linked with the RAPD markers. Moran's I spatial autocorrelation coefficient revealed weak genetic structure, 29.09% Moran's I-values were significantly greater than expected value, and 45.5% of I-correlograms were significantly deviated from randomness. The results indicated a low level of allele clustering. The random distribution of individuals may be the result of high mortality rate of seedlings, whereas the positive autocorrelation over short distance class may be the result from the limited seed dispersal, and the genetic structure may be weaken by overlapping seed shadow and high mortality rate of seedling. The results have important implications for the conservation and management of P. chinensis, especially for the sampling strategies of ex situ conservation. 5. The ex situ conserved population (ML) of P. chinensis contained an intermediate genetic variation, with 20.84% bands being polymorphic. Of the total 253 bands generated in P. chinensis, 195 bands were also detected in population ML, indicating that 77.08% of the total genetic variations of this species were conserved in ex situ population. If only the alleles with moderate to high frequency (P>0.05) were considered, 171 out of 187 bands (91.44%) occurred in ex situ population ML. RAPD analysis also detected some exclusive bands in natural populations, while none of those bands were detected in ex situ conserved population ML. The populations conserved in the National Nature Reserve contained a large part of genetic variation of the whole species. Of the total 253 RAPD bands detected in P. chinensis, 221 bands occurred in in situ populations, which indicated that 87.35% of the total genetic variations of this species were conserved in natural reserve. If only the alleles with moderate to high frequency (P>0.05) were considered, 179 out of 187 bands (95.72%) occurred in in situ conserved populations. Our conclusions are that the ex situ conserved populationML doesn't contain enough genetic variation to meet the need of release in future, and that more extensive ex situ sampling in natural population TY, NP, HK, and MG is needed to conserve more exclusive alleles in ex situ population, while the in situ conserved population contains representative genetic variation to maintain long-term survival and evolutionary process of P. chinensis. Furthermore, the systematic position of P. chinensis of Dipterocarpaceae was investigated by using nucleotide sequences of matK, trnL intron and trnL-trnF intergenic spacer region in Chloroplast DNA. Phylogenetic analysis was performed by the maximum parsimony method. The analysis indicates high support (bootstrap probabilities 80%) for placing P. chinensis within genus Parashorea, rather than within genus Shorea. Moreover, P. chinensis Wang Hsie and P. chinensis Wang Hsie var. kwangsiensis Lin Chi were evaluated the same species, which consisted with their morphological data.
|
PDF Full Text Request