Genetic Differentiation and Relationship among Castanopsis chinensis, C. qiongbeiensis, and C. glabrifolia (Fagaceae) as Revealed by Nuclear SSR Markers.

Castanopsis chinensis (Spreng.) Hance is widespread in the subtropical forests of China. Castanopsis qiongbeiensis G.A. Fu and Castanopsis glabrifolia J. Q. Li & Li Chen are limited to the coastal beaches of Wenchang county in the northeast of Hainan Island, and have similar morphological characteristics to C. chinensis. It is supposed that C. qiongbeiensis and C. glabrifolia are closely related to C. chinensis. In the present study, the genetic differentiation, gene flow, and genetic relationship of C. chinensis, C. qiongbeiensis, and C. glabrifolia were investigated by using 15 nuclear microsatellite markers; a total of 308 individuals from 17 populations were sampled in the three species. The allelic variation of nuclear microsatellites revealed moderate but significant genetic differentiation (FCT = 0.076) among C. chinensis, C. qiongbeiensis, and C. glabrifolia, and genetic differentiation between C. chinensis and C. glabrifolia was larger than that between C. chinensis and C. qiongbeiensis. Demographic simulations revealed unidirectional gene flow from C. chinensis to C. glabrifolia and C. qiongbeiensis, which highlight dispersal from mainland to island. The isolation effect of Qiongzhou Strait increased the genetic differentiation of species on both sides of the strait; however, the differentiation was diminished by gene flow that occurred during the historical period when Hainan Island was connected to mainland China. Our results supported the argument that C. glabrifolia should be considered an independent species and argued that C. qiongbeiensis should be regarded as an incipient species and independent conservation unit.

Species Delimitation and Genetic Relationship of Castanopsis hainanensis and Castanopsis wenchangensis (Fagaceae).

Castanopsis is one of the most common genus of trees in subtropical evergreen broad-leaved forests and tropical monsoon rainforests in China. Castanopsis hainanensis and Castanopsis wenchangensis are endemic to Hainan Island, but they were once confused as the same species due to very similar morphologies. In this study, nuclear microsatellite markers and chloroplast genomes were used to delimit C. hainanensis and C. wenchangensis. The allelic variations of nuclear microsatellites revealed that C. hainanensis and C. wenchangensis were highly genetically differentiated with very limited gene admixture. Both showed higher genetic diversity within populations and lower genetic diversity among populations, and neither had further population genetic structure. Furthermore, C. wenchangensis and C. hainanensis had very different chloroplast genomes. The independent genetic units, very limited gene admixture, different distribution ranges, and distinct habitats all suggest that C. wenchangensis and C. hainanensis are independent species, thus they should be treated as distinct conservation units.

Demographic Inference of Divergence and Gene Exchange Between Castanopsis fabri and Castanopsis lamontii.

The cytoplasmic genome of one species may be replaced by that of another species without leaving any trace of past hybridization in its nuclear genome, which can thus confuse the inference of genealogical relationship and evolutionary history of many congeneric species. In this study, we used sequence variations of chloroplast DNA and restriction site-associated DNA to investigate gene exchange between Castanopsis fabri and Castanopsis lamontii, and to infer the divergence history of the two species by comparing different divergence models based on the joint allele frequency spectrum. We evaluated climatic niche similarity of the two species using climatic variables across their entire distribution range in subtropical China. Clear genetic differentiation was revealed between C. fabri and C. lamontii, and gene exchange between the two species was discovered as a consequence of secondary contact. The gene exchange rates were variable across the genome. Gene exchange could allow C. fabri to widen its habitat through pollen swamping and broaden its climatic niche, and the chloroplast genome of C. lamontii is captured by C. fabri during this process. These results further our understanding of the timing and contribution of gene exchange to species divergence in forests.

Translocation of threatened plants as a conservation measure in China.

We assessed the current status of plant conservation translocation efforts in China, a topic poorly reported in recent scientific literature. We identified 222 conservation translocation cases involving 154 species, of these 87 were Chinese endemic species and 101 (78%) were listed as threatened on the Chinese Species Red List. We categorized the life form of each species and, when possible, determined for each case the translocation type, propagule source, propagule type, and survival and reproductive parameters. A surprisingly large proportion (26%) of the conservation translocations in China were conservation introductions, largely implemented in response to large-scale habitat destruction caused by the Three-Gorge Dam and another hydropower project. Documentation and management of the translocations varied greatly. Less than half the cases had plant survival records. Statistical analyses showed that survival percentages were significantly correlated with plant life form and the type of planting materials. Thirty percent of the cases had records on whether or not individuals flowered or fruited. Results of information theoretic model selection indicated that plant life form, translocation type, propagule type, propagule source, and time since planting significantly influenced the likelihood of flowering and fruiting on the project level. We suggest that the scientific-based application of species conservation translocations should be promoted as part of a commitment to species recovery management. In addition, we recommend that the common practice of within and out of range introductions in nature reserves to be regulated more carefully due to its potential ecological risks. We recommend the establishment of a national office and database to coordinate conservation translocations in China. Our review effort is timely considering the need for a comprehensive national guideline for the newly announced nation-wide conservation program on species with extremely small populations, which is expected to stimulate conservation translocations for many species in the near future.

High genetic diversity and low differentiation of Michelia coriacea (Magnoliaceae), a critically endangered endemic in Southeast Yunnan, China.

Michelia coriacea, a critically endangered tree, has a restricted and fragmented distribution in Southeast Yunnan Province, China. The genetic diversity, genetic structure and gene flow in the three extant populations of this species were detected by 10 inter-simple sequence repeat (ISSR) markers and 11 simple sequence repeat (SSR) markers. Examination of genetic diversity revealed that the species maintained a relatively high level of genetic diversity at the species level (percentage of polymorphic bands) PPB = 96.36% from ISSRs; PPL (percentage of polymorphic loci) = 95.56% from SSRs, despite several fragmental populations. Low levels of genetic differentiation among the populations of M. coriacea were detected by Nei's G(st) = 0.187 for ISSR and Wright's F(st) = 0.090 for SSR markers, which is further confirmed by Bayesian model-based STRUCTURE and PCoA analysis that could not reveal a clear separation between populations, although YKP was differentiated to other two populations by ISSR markers. Meanwhile, AMOVA analysis also indicated that 22.84% and 13.90% of genetic variation existed among populations for ISSRs and SSRs, respectively. The high level of genetic diversity, low genetic differentiation, and the population, structure imply that the fragmented habitat and the isolated population of M. coriacea may be due to recent over-exploitation. Conservation and management of M. coriacea should concentrate on maintaining the high level of genetic variability through both in and ex-situ conservation actions.

Genetic diversity and population structure of two important medicinal plant species Schisandra chinensis and Schisandra sphenanthera revealed by nuclear microsatellites.

Seven polymorphic and transferable nuclear microsatellites were used to investigate the population structure of genetic diversity of Schisandra chinensis and Schisandra sphenanthera for facilitating their conservation and sustainable utilization. High levels of gene diversity were revealed in these two medicinal species, the majority of genetic diversity was harbored within populations, and population structure was might due to restricted gene flow among populations. Isolation by distance was close to significance in S. chinensis but not in S. sphenanthera. In S. chinensis, null alleles were identified as a cause for excess of homozygotes at loci G24 and WGA60, but inbreeding might also be partly responsible for the positive F ( IS ) values in this species. In contrast, null allele frequencies were high at all the seven loci in S. sphenanthera and resulted in overestimation of fixation index. The strategy for ex situ conservation of these two medicinal species is discussed based on the genetic results.

Genetic diversity and differentiation of Michelia maudiae (Magnoliaceae) revealed by nuclear and chloroplast microsatellite markers.

Michelia maudiae Dunn. is a Magnoliaceae species threatened by habitat destruction and over-exploitation. Genetic diversity and differentiation, population contribution to total diversity and allelic/haplotypic richness, and the relative importance of pollen- and seed-mediated gene flow were investigated in nine populations (192 individuals) of M. maudiae using nuclear and chloroplast microsatellites to further our understanding of the genetic structure and evolutionary history of this tree species and to provide a genetic perspective for its conservation. The species had strong pollen mediated gene flow in the past. The ratio of pollen to seed gene flow was 25.4. Three clusters from the western, central, and eastern China were identified by both chloroplast and nuclear microsatellites. Western populations at Xiaodanjiang and Daoxian were phylogenetically divergent from the remaining populations and might be particularly important for the conservation of this species. The populations of Xiaodanjiang, Daoxian, and Minjiangyuan made positive contribution to the total diversity and allelic/haplotypic richness, and were worthy of being conserved with priority. In the central cluster, population at Laopengding should be protected since it harbored the greatest genetic diversity.