Multi-scale Spatial Genetic Structure And Population Demographic History Of Torreya Jackii (Taxaceae), An Endemic And Endangered Plant In China

The genetic structure of a species plays a crucial role in its survival and development. Exploring genetic diversity and their distribution of endangered species can lay the basis for reasonable and effective protection strategy. Zhejiang-Fujian Mountains is one of the key terrestrial biodiversity hotspots in China. Genetic structure and population history can indicate the evolution and ecological processes of the plant and the biodiversiy maintaining mechanisms in this area. At the same time, it is important for the theoretical and practical biodiversity consevation. Torreya jackii Chun (Taxaceae) is an endangered species endemic to this area. Multi-scale spatial genetic structure of T. jackii were studied using SSR molecular marker. In addition, we combined the variation information of the chloroplast DNA and mitochondria DNA to infer the population demographic history which can provide scientific basis for the further protection. It can also provide a reference for the study of the evolutionary history of the endemic species in the Zhejiang-Fujian Mountains. The main results were as following.1. Eight polymorphic microsatellite primers were developed for T. jackii to investigate the genetic structure using the improved biotin-streptavidin capture method.2. We analyzed the genetic structure of all populations collected in the whole distritution areas using8pairs of SSR markers. Fourty-two alleles were found. The observed heterozygosity were0.3641～0.6336with an average of0.5012. The expected heterozygosity ranged from0.3657to0.6047with an average of0.4830. AMOVA analysis showed that the genetic variation was mainly found within population, the genetic differentiation among populations was low (FST=0.155, RST=0.195). STRUCTURE cluster analysis and PCoA analysis showed that there have a higher mixing ratio among populations. Mantel test showed that there was no significant relationship between genetic distance and geographic distance. The effective population size ranged from15.12to185.48with an average of44.08. BOTTLENECK analysis showed that recent bottleneck effects were found in population of Jinyun, Shaowu, Yonjia, Xianju and Songyang. In terms of the population genetic contribution, population Jinyun, Songyang, Tonglu, Xianju was comparatively large. So, we suggested that those four populations should be the priority to be protected.3. The spatial genetic structure (SGS) of the subpopulations were studied using SSR markers. Fourty-one alleles were found in the7subpopulations using8pairs of SSR primers. The observed heterozygosity were0.4688～0.6027with the average of0.5427. The expected heterozygosity ranged from0.4453to0.5471with the average of0.5060. AMOVA analysis showed that the genetic variation was mainly found within subpopulation, the genetic differentiation among subpopulations was low (FST=0.064, RST=0.089). Significant SGS occurred in all individuals and each age level of the T.jackii in fine-scale, and the SGS intensity of the seedlings and juveniles were greater than the adult trees. The effective gene dispersal distance of T. jackii was23.79m. Judging from the distribution area of the7subpopulations, significant SGS was found in the0～0.4km regional scale.4. Among39cpDNA fragments screened, four, i.e., trnD-trnT, atpH-atpI, rpoB-trnC and rps16-trnQ, were polymorphic. Joint analysis of these four fragments, We found6haplotypes. One common haplotype was found in all populations, and the other five were unique haplotype, existing in population Songyang, Xianju, Zixi and Pucheng, respectively. The haplotype diversity was0.168. The genetic differentiation value (FST) was0.188, GST was0.221. AMOVA analysis showed that the genetic variation was mainly found within population. Neutrality test (including Tajima’s and Fu’s Fs) and mismatch analysis indicated that each population of T. jackii had not undergone recent population expansion, but in its whole species level had undergone recent expansion. H1was the center of the TCS network. cpDNA haplotypes relationship was "star-like", with five rare haplotypes linked to the ancestral interior haplotype H1. Both MP and Bayesian tree showed that the six haplotypes did not form distinct separated clades. Using a fossil come from Taxaceae for calibration, we obtained the divergence time of these6haplotypes began about14.37million years ago by calculating with molecular clock model.5. Only mitochondria fragment coxI was variable among the18pairs of primers, and two haplotypes were found. Unique haplotype was found in population Pucheng, another one was shared in all populations. The haplotype diversity of mitochondria fragments was0.022. The genetic differentiation value (FST) was0.333, GST was0.316. AMOVA analysis showed that the genetic variation was mainly found within population.6. Population dynamics analysis by msvar based on Bayesian method showed that the current population size of T. jackii was4417.74, which was2.27times larger than the ancestral populations (1945.36), which indicated that the population of T. jackii had undergone expansion. Further analysis showed that the expantion time was about2351.26～12909.22years ago.