Jinju Zhang

Chloroplast microsatellite markers in Liriodendron tulipifera (Magnoliaceae) and cross-species amplification in L. chinense

PREMISE OF THE STUDY A set of cpSSR markers were developed for the tree genus Liriodendron L. to investigate population genetic structure and phylogeographic history. METHODS AND RESULTS Primers were designed directly from the chloroplast genome sequences of Liriodendron tulipifera. Among the 55 cpSSR markers tested, 11 polymorphic markers were identified in L. tulipifera. The number of alleles in the population tested ranged from two to five, and the unbiased haploid diversity per locus ranged from 0.074 to 0.644. Eighteen primer pairs generated polymorphic amplification in L. chinense. The number of alleles per locus ranged from two to seven, and the unbiased haploid diversity per locus was from 0.250 to 0.964. CONCLUSIONS cpSSR markers developed here will be useful for phylogeography and population genetics studies of Liriodendron.

Fine‐scale spatial genetic structure and gene flow in a small, fragmented population of Sinojackia rehderiana (Styracaceae), an endangered tree species endemic to China

Populations of Sinojackia rehderiana are highly threatened and have small and scattered distribution due to habitat fragmentation and human activities. Understanding changes in genetic diversity, the fine-scale spatial genetic structure (SGS) at different life stages and gene flow of S. rehderiana is critical for developing successful conservation strategies for fragmented populations of this endangered species. In this study, 208 adults, 114 juveniles and 136 seedlings in a 50 × 100-m transect within an old-growth forest were mapped and genotyped using eight microsatellite makers to investigate the genetic diversity and SGS of this species. No significant differences in genetic diversity among different life-history stages were found. However, a significant heterozygote deficiency in adults and seedlings may result from substantial biparental inbreeding. Significant fine-scale spatial structure was found in different life-history stages within 19 m, suggesting that seed dispersal mainly occurred near a mother tree. Both historical and contemporary estimates of gene flow (13.06 and 16.77 m) indicated short-distance gene dispersal in isolated populations of S. rehderiana. The consistent spatial structure revealed in different life stages is most likely the result of limited gene flow. Our results have important implications for conservation of extant populations of S. rehderiana. Measures for promoting pollen flow should be taken for in situ conservation. The presence of a SGS in fragmented populations implies that seeds for ex situ conservation should be collected from trees at least 19-m apart to reduce genetic similarity between neighbouring individuals.

Spontaneous Interspecific Hybridization and Patterns of Pollen Dispersal in Ex Situ Populations of a Tree Species (Sinojackia xylocarpa) that is Extinct in the Wild

For endangered plants interspecific hybridization occurring in ex situ collections may lead to failure of reintroduction actions. We used Sinojackia xylocarpa, a well documented Chinese endemic species that is extinct in the wild, as a model case to address this concern. We used paternity analyses to assess the spontaneous hybridization and patterns of pollen flow between S. xylocarpa and its congener species, S. rehderiana, in conserved populations in Wuhan Botanic Garden. Interspecific hybridization events were detected in seven out of eight maternal trees of S. xylocarpa, and an average of 32.7% seeds collected from maternal trees of S. xylocarpa were hybrids. The paternity of 93 out of 249 seedlings from S. xylocarpa assigned to S. rehderiana provided convincing evidence that spontaneous interspecific hybridization occurred extensively in the living garden collection we studied. Different patterns of pollen dispersal (predominantly short-distance vs. long-distance pollination) were observed between intra- and interspecific hybridization events in the garden. Pollen dispersal within the ex situ populations was not restricted by distance, as evidenced by a lack of significant correlations between the average effective pollen dispersal distance (delta) and the geographic distances (d1 and d2) between maternal and paternal trees. The interspecific pollen-dispersal distance ranged from 10 to 620.1 m (mean 294.4 m). Such extensive hybridization in ex situ collections could jeopardize the genetic integrity of endangered species and irrevocably contaminate the gene pool if such hybrids are used for reintroduction and restoration. We recommend strongly that measures be taken to minimize the genetic risks of this kind of hybridization, including establishing buffer zones in ex situ collections, manipulating flowering phenology, testing seed lots before use in reintroduction programs, and controlling pollination for seed purity.

Phylogeography and genetic structure of a Tertiary relict tree species, Tapiscia sinensis (Tapisciaceae): implications for conservation

BACKGROUND AND AIMS The phylogeography of plant species in sub-tropical China remains largely unclear. This study used Tapiscia sinensis, an endemic and endangered tree species widely but disjunctly distributed in sub-tropical China, as a model to reveal the patterns of genetic diversity and phylogeographical history of Tertiary relict plant species in this region. The implications of the results are discussed in relation to its conservation management. METHODS Samples were taken from 24 populations covering the natural geographical distribution of T. sinensis. Genetic structure was investigated by analysis of molecular variance (AMOVA) and spatial analysis of molecular variance (SAMOVA). Phylogenetic relationships among haplotypes were constructed with maximum parsimony and haplotype network methods. Historical population expansion events were tested with pairwise mismatch distribution analysis and neutrality tests. Species potential range was deduced by ecological niche modelling (ENM). KEY RESULTS A low level of genetic diversity was detected at the population level. A high level of genetic differentiation and a significant phylogeographical structure were revealed. The mean divergence time of the haplotypes was approx. 1·33 million years ago. Recent range expansion in this species is suggested by a star-like haplotype network and by the results from the mismatch distribution analysis and neutrality tests. CONCLUSIONS Climatic oscillations during the Pleistocene have had pronounced effects on the extant distribution of Tapiscia relative to the Last Glacial Maximum (LGM). Spatial patterns of molecular variation and ENM suggest that T. sinensis may have retreated in south-western and central China and colonized eastern China prior to the LGM. Multiple montane refugia for T. sinense existing during the LGM are inferred in central and western China. The populations adjacent to or within these refugia of T. sinense should be given high priority in the development of conservation policies and management strategies for this endangered species.

Characterization of 39 novel EST-SSR markers for Liriodendron tulipifera and cross-species amplification in L. chinense (Magnoliaceae).

PREMISE OF THE STUDY A novel set of simple sequence repeat (SSR) markers were developed and characterized from the expressed sequence tag (EST) database of Liriodendron tulipifera for application in population genetic studies of Liriodendron. METHODS AND RESULTS Thirty-nine polymorphic EST-SSR loci were identified among 27 individuals sampled from a cultivated population of L. tulipifera. The number of alleles per locus ranged from three to 18. The average observed heterozygosity and expected heterozygosity were 0.684 and 0.778, respectively. Of the 39 loci, 32 showed interspecific transferability and polymorphism in a related species, L. chinense. The number of alleles per locus ranged from two to 11, and the average observed heterozygosity and expected heterozygosity were 0.475 and 0.736, respectively. CONCLUSIONS The developed EST-SSR markers will be useful for investigating adaptive genetic differentiation in Liriodendron.

Development and Characterization of 11 Polymorphic Microsatellite Markers in Tapiscia sinensis (Staphyleaceae)

Premise of the study: We developed and characterized five polymorphic microsatellite loci from an AC-enriched genomic library of a rare tree, Tapiscia sinensis, and six compound microsatellite primers using a dual-suppression-PCR–based approach, to investigate geographical genetic structure. Methods and Results: The polymorphism of these loci was assessed in 102 samples collected from three populations. The number of alleles per locus ranged from one to nine. Expected heterozygosity per locus ranged from 0.000 to 0.709 and observed heterozygosity ranged from 0.000 to 0.750. Five loci deviated from Hardy–Weinberg equilibrium after Bonferroni correction. Conclusions: This set of microsatellites may be useful for investigating broad-scale genetic variation in the extant populations of the endangered tree species T. sinensis.

Characterization and Development of EST-Derived SSR Markers in Sinowilsonia henryi (Hamamelidaceae)

Premise of the study: Polymorphic microsatellite markers were developed to reveal the genetic diversity of extant populations and the mating system of Sinowilsonia henryi (Hamamelidaceae). Methods and Results: In this study, nuclear simple sequence repeat (SSR) markers were developed using the Illumina high-throughput sequencing technique (RNA-Seq). The de novo–assembled transcriptome generated a total of 64,694 unique sequences with an average length of 601 bp. A total of 2941 microsatellite loci were detected. Of the 121 tested loci, 13 loci were polymorphic and eight were monomorphic among 72 individuals representing three natural populations of the species. The number of alleles per locus ranged from one to four, and the observed and expected heterozygosity at population level were 0.00–1.00 and 0.10–0.66, respectively. Conclusions: The developed expressed sequence tag (EST)–SSRs will be useful for studying genetic diversity of S. henryi as well as assessing the mating system among Sinowilsonia species.