|其他题名||Species Delimitation and Conservation Genetics of Taxus fuana Nan Li & R.R. Mill (Taxaceae) in Pakistan
|其他摘要||Taxus fuana Na Li & R. R. Mill, an endangered species, is endemic to the Western Himalayas. Recent deforestation and overexploitation have driven numerous wild populations of the species into the extinction, and surviving populations are rapidly declining in size. The extent and distribution of genetic variation within a species is of fundamental importance to understand its evolutionary potential, and thus determine its survival. Assessment of genetic variation within endangered populations is perquisite for effective conservation strategies.
The nomenclature and taxonomic status of Taxus in the Western Himalayas has long been problematic. Twenty-seven morphological characters, 62 selected herbarium specimens of T. wallichiana, T. baccata and tentatively identified T. fuana were used to investigate the taxonomic status of Taxus in Pakistan by means of principal component analysis (PCA). Three discrete clusters representing the three species were observed in the PCA scatter plots. Character combinations allowed reliable identification of specimens of T. wallichiana, T. baccata and T. fuana, while sequence data of nrDNA ITS and the chloroplast trnL-F region were used to further delimit T. wallichiana, T. baccata and T. fuana. Using maximum parsimony analysis three distinct clades were obtained representing the three species. Based on both morphological and molecular data, the Taxus species occurring in the Western Himalayas including Pakistan was shown to be T. fuana and not T. wallichiana or T. baccata.
Levels of genetic variation and pattern of population structure within and among 10 wild T. fuana populations from Pakistan were investigated. The results showed that there is a low level of genetic diversity within population and a significant genetic differentiation among populations was detected (ΦST = 0.5685). The gene flow was low with an estimate of Nm = 0.3558. As a consequence of habitat fragmentation, evolutionary factors including genetic drift and limited gene flow may be responsible for the above-mentioned findings. Based on these findings, conservation concerns are discussed together with possible strategies for implementing in situ and ex situ conservation.
The morphological characters were analyzed by using data processing system (DPS) and principal component analysis (PCA). The results indicated that continuous characters were significantly determined by ecological factors. No significant correlation between genetic distance and Euclidean distance was present. While there is correlation between Euclidean distances and geographical distances by Mantel test in the 10 sampled populations of T. fuana. No correlation between the morphological and molecular data was found.
Of 12 regions of chloroplast DNA screened by using nine restriction enzymes with PCR-RFLP, in only one region (trnL-F) was a usable polymorphism detected. Only two PCR-RFLP haplotypes were distinguished in the 10 populations. Haplotype 1 was widespread and fixed in all sampled populations, while the private haplotype 2 was detected in a single individual of population SW. Haplotype 2 might be derived from Haplotype 1 by two mutational steps. No phylogeographic pattern in T. fuana in Pakistan was resolved due to limited haplotypes detected in the present study. The chloroplast DNA variation of T. fuana was much lower than that of other gymnosperm species, which possibly resulted from its evolutionary history.|
MuhammadAminUllahShahAmin. 密叶红豆杉的种级界定和保护遗传学研究[D]. 昆明植物研究所. 中国科学院昆明植物研究所,2007.