自然杂交对濒危植物越南青冈遗传多样性和适应性的影响

Hybridization between a rare species and a sympatric common closely related species can cause genetic assimilation of the rare species through asymmetrical introgression. Furhtermore, outbreeding depression and habitat overlap can facilitate competition for suitable site and threaten the persistence of the parental taxa, especially those in small populations. More attentions are raised to the effects of hybridization to rare plant species,but the related studies are limited and lacking quantitative evidence. Based on our previous study, an endangered species Quercus austrocochinensis can naturally hybridize with a symmetric common species Q. kerrii, which may increase its risk to extinct. The objectives of this study will apply population demography, population genetics, ecological and physiological approches to reveal: 1) the hybridization frequency between Q. austrochochinensis and Q. kerrii; 2) ratio of hybrid offsprings backcrossing to parental species; 3) whether asymmetrical introgression from Q. kerrii to Q. austrocochinensis happened and eventually led to genetic assimilation of Q. austrocochinensis; 4) the correlation between asymmetrical introgression direction and paraental taxa abundance; 5) to examine ecological differentiation of Q. kerrii, endangered Q. austrocochinensis and their hybrids. Based on assessing population structure, incorporating the effects of hybridization on Q. austrocochinensis, the strategies and management policies to conserve this endangered species will be given. This study can offer a model system to quantitatively study the hybridization effects to genetic and ecological diffieretions of endangered wind-pollinated tree species.

植物稀有种和近缘常见种杂交可能通过不对称基因渐渗使稀有种被常见种遗传同化导致遗传灭绝。同时远交衰退、杂交后代与亲本竞争相同生境，可能使稀有种亲本更加濒危。杂交效应在稀有种保护中逐渐受到重视，但相关研究较为薄弱。申请者前期研究发现栎属濒危种越南青冈与同域常见种毛叶青冈存在自然杂交，可能增加它灭绝的风险。本项目综合应用种群统计学、群体遗传学、生理生态手段，探索1)越南青冈与毛叶青冈之间的自然杂交的程度如何？2)杂交后代是否与毛叶青冈发生回交的几率更大,并导致越南青冈被毛叶青冈逐步遗传同化？3)杂交过程中是否存在毛叶青冈对越南青冈的不对称基因渐渗？4)不对称基因渐渗的方向与亲本相对多度有何联系？ 5)杂交后代及亲本生态适应有何异同？在此基础上综合评价杂交对越南青冈的影响，从保护遗传学角度为合理制定越南青冈的保护对策提供理论依据，并为植物稀有种与常见种间杂交的遗传和生态效应深入研究提供定量证据。

植物稀有种和近缘常见种杂交可能通过不对称基因渐渗使稀有种被常见种遗传同化导致遗传灭绝。同时远交衰退、杂交后代与亲本竞争相同生境，可能使稀有种亲本更加濒危。栎属濒危种越南青冈与同域常见种毛叶青冈存在自然杂交，但杂交对其遗传多样性的影响尚无研究。本项目综合应用形态学、群体遗传学、生理生态等手段对越南青冈与毛叶青冈间的杂交渐渗进行研究，结果表明叶下表皮毛被和叶表皮细胞形态可以用于杂交个体和两个亲本的鉴定。基于毛叶青冈和越南青冈转录组测序获取了21对在两个种间具有较高多态性的SSR位点。基于SSR和AFLP标记对不同区域越南青冈群体/亚群体的遗传组成分析研究结果显示，杂交渐渗普遍存在于中国分布的两个越南青冈居群中，仅有西双版纳自然保护区勐养片区核心区的亚群体还保持有特别的遗传组成，其它位于西双版纳保护区的越南青冈亚群体及海南分布居群与毛叶青冈发生杂交渐渗，在局部区域形成了杂交池。越南青冈表型在沟谷生境中受到选择，分子鉴定为遗传纯正的越南青冈个体比形态所获越南青冈个体少，濒危等级高于预期。两个种的杂交带动态与人为干扰密切相关。对越南青冈引种苗的光合、温度生理研究和引种观察表明，越南青冈种子为典型顽拗性种子，种子成熟后立即萌发，随后上胚轴休眠3-4个月。高湿度有利于其幼苗建植成活，在苗期越南青冈较毛叶青冈具有的对低光更好的适应，可能是其在林窗下不易成活的重要原因。越南青冈叶片高温半致死温度均为42℃可左右，茎段高温半致死温度为46℃，叶和茎段的低温半致死温度为-2℃及-10℃左右，这一结果与栽培实验结果一致。本次研究对越南青冈的保育研究提供了重要基础资料。