title: Introgression Threatens the Genetic Diversity ofQuercus austrocochinchinensis(Fagaceae), an Endangered Oak: A Case Inferred by Molecular Markers.
abstract: Natural introgression can cause negative effects where rare species experience genetic assimilation and invade by their abundant congeners.Quercus austrocochinchinensisandQ. kerrii(subgenusCyclobalanopsis) are a pair of closely related species in the Indo-China area. Morphological intermediates of the two species have been reported in this region. In this study, we used AFLP, SSR and two key leaf morphological diagnostic traits to study the twoQ.austrocochinchinensispopulations, two pureQ. kerriiand two putative hybrid populations in China. Rates of individual admixture were examined using the Bayesian clustering programs STRUCTURE and NewHybrids, with no a priori species assignment. In total, we obtained 151 SSR alleles and 781 polymorphic loci of AFLP markers. Population differentiation inferred by SSR and AFLP was incoherent with recognized species boundaries. Bayesian admixture analyses and principal coordinate analysis identified more hybrids and backcrossed individuals than morphological intermediates in the populations. SSR inferred a wide genetic assimilation inQ. austrocochinchinensis, except for subpopulation D2 in the core area of Xi-Shuang-Ban-Na Nature Reserve (XSBN). However, AFLP recognized moreQ. austrocochinchinensispurebreds than SSR. Analysis using NewHybrids on AFLP data indicated that these hybridized individuals were few F2and predominantly backcrosses with both parental species. All these evidences indicate the formation of a hybrid swarm at XSBN where the two species co-exist. Both AFLP and SSR recognized that the core protected area of XSBN (D2) has a high percentage ofQ. austrocochinchinensispurebreds and a unique germplasm. The Hainan population and the other subpopulations of XSBN of the species might have lost their genetic integrity. Our results revealed a clear genetic differentiation in the populations and subpopulations ofQ. austrocochinchinensisand ongoing introgression betweenQ. austrocochinchinensisandQ. kerriiat the disturbed contact areas. Combining the results from genetic and morphological analyses, the conservation of subpopulation D2 should be prioritized. Conservation and restoration of the integrity of tropical ravine rainforest is an important long-term goal for the successful conservation ofQ. austrocochinchinensis. The fine-scale landscape might play an essential role in shaping the spatial patterns of hybridization. Further studies are needed to evaluate these patterns and dynamics.
authors.affiliation: Shanghai Key Laboratory of Plant Functional Genomics and Resources, Shanghai Chenshan Botanical GardenShanghai, China; Shanghai Chenshan Plant Science Research Center, Chinese Academy of SciencesShanghai, China.
authors.forename: Miao
authors.initials: M
authors.lastname: An
authors.affiliation: Shanghai Key Laboratory of Plant Functional Genomics and Resources, Shanghai Chenshan Botanical GardenShanghai, China; Shanghai Chenshan Plant Science Research Center, Chinese Academy of SciencesShanghai, China.
authors.forename: Min
authors.initials: M
authors.lastname: Deng
authors.affiliation: Shanghai Key Laboratory of Plant Functional Genomics and Resources, Shanghai Chenshan Botanical GardenShanghai, China; Shanghai Chenshan Plant Science Research Center, Chinese Academy of SciencesShanghai, China.
authors.forename: Si-Si
authors.initials: SS
authors.lastname: Zheng
authors.affiliation: Shanghai Key Laboratory of Plant Functional Genomics and Resources, Shanghai Chenshan Botanical GardenShanghai, China; Shanghai Chenshan Plant Science Research Center, Chinese Academy of SciencesShanghai, China.
authors.forename: Xiao-Long
authors.initials: XL
authors.lastname: Jiang
authors.affiliation: Shanghai Key Laboratory of Plant Functional Genomics and Resources, Shanghai Chenshan Botanical GardenShanghai, China; Shanghai Chenshan Plant Science Research Center, Chinese Academy of SciencesShanghai, China.
authors.forename: Yi-Gang
authors.initials: YG
authors.lastname: Song
keywords: AFLP; Quercus subgenus Cyclobalanopsis; SSR; endangered species; introgression