Genetic Diversity Of Four Chinese Cypress Species (Cupressus L.)

Biological diversity is fundamental to the subsistence of human beings, and genetic diversity is an essential element of biological diversity. Genetic diversity is a prerequisite for the potential for evolutionary response to eviromental changes. Meanwhile, researches on genetic diversity provide basic information for the conservation of rare biological resources. Here we report such a case study on four putative cypress (Cupressus L.) species, C. chengiana, C. duclouxiana, C. gigantea and C. funebris, which are distributed in the Qinghai-Tibetan Plateau (QTP) and adjacent regions. Among these, C. chengiana and C. duclouxiana were listed in the Red List of Endangered Plants in China as second-class threatened plant species. As habitats of these endemic or endangered plant species have been undermined during recent years as a result of global climate changing as well as increasing human acitivities, their populations are under a threatened situation. It is therefore imperative to examine their genetic diversity and rule out effective conservation strategies accordingly.In this study, genetic diversity, genetic structure and infra-species genetic differentiation of these four species were surveyed using SSR molecular markers, and reasonable suggestions were proposed for the preservation of each species. After preliminary investigation,6 out of 53 loci were found to be polymorphic. These 6 loci were employed to detect genetic diversity of 145 C. chengiana individuals (9 populations),94 C. gigantea indivihuals (6 populations),141 C. duclouxiana individuals (10 populations) and 105 C. funebris individuals (10 populations), totaling 485 individuals from 35 populations. Analysis of molecular variance (AMOVA) showed that the genetic variation was found mainly among species (19.62%) rather than within populations (9.98%), but no relevant regional differentiation was discernible. Total genetic variation of C. chengiana and C. duclouxiana are far higher than that of C. funebirs and C. gigantea. FsT analysis also indicated comparatively high genetic differentiation among species and between distribution regions. In addition to these, STRUCTURE analyses reveal high genetic differentiation among species, as well as among two geographic lineages within C. chengiana and C. duclouxiana, respectivly. According to these results, specific conservation strategies were put forward for these four species. For C. chengiana and C. duclouxiana, two effective management units within each of them should be established; meanwhile, in situ and ex situ preservation of these species should include as much natural populations as possible. Rigorous conservation and artificial recruitments of current populations are suggested for C. gigantea. The widesperead C. funebirs is of low genetic diversity, and there is no alternative but keep current populations.