【作者】 予茜；

【导师】 郭友好；

【作者基本信息】 武汉大学 ， 植物学， 2011， 博士

【摘要】 引入物种在新生境中,从宏观至微观的性状都常常具有相对快速发生变化的潜能。在引入地成功建群、繁殖扩散成为入侵物种的生物都经历了对入侵地的适应性进化。所以入侵性物种是研究物种分化及局域适应非常合适的系统。研究入侵性物种的分化和适应机制对理解生物入侵现象和研究防控手段等各个方面都具有积极的意义。本研究选取两种入侵性杂草物种为对象,收集了两物种原产地和入侵地自然居群种子,采用生态学、数量遗传学以及基因组学方法研究了不同产地居群后代在表型和遗传水平的分化程度,并用数量遗传学方法评估了遗传分化的原因是自然选择还是随机遗传漂变。探讨了研究物种可能的入侵地适应机制。具体研究内容及结果如下：1.我们以三裂叶豚草(Ambrosia trifida)为研究材料,使用来自原产地美国和入侵地中国的自然居群的种子在温室里同样的环境条件下各培育了数个实验居群,对比了母本种子特征,实验居群植株生长、繁殖表型,核DNA含量以及对干旱、营养、模拟虫害胁迫的抗性等方面差异。研究结果显示：从自然居群种子特征来看,三裂叶豚草在入侵地所受虫害显著低于原产地,具有天敌逃逸的优势。实验居群植株在早期生长中表现出植株形状的差异,入侵地植株更高而窄,差异到生长中后期则不明显。这种资源配置方式可能有利于入侵地植株在生长早期获得更多的阳光,以与周围伴生种竞争资源。入侵地植株开花的时期较原产地更早,这一极显著差异表现出入侵地植株较原产地植株已经发生了向更快速完成生活史的明显转化。两地居群的抗旱和耐营养胁迫能力相当,但遭受模拟虫害胁迫时,入侵地居群生长和繁殖表现显著降低,而原产地居群反应不明显。该种入侵地居群对虫害胁迫的敏感支持了增强竞争能力(EICA)的假说。另外,入侵地居群在生长特性上具有更高的表型可塑性,使其既能在营养或其它方面受到胁迫时保持一定水平的繁殖量,而且在条件更好时能够增加繁殖量以使繁殖表现最大化。因此表型可塑性可能对其入侵的成功起到了积极的作用。同时,我们在入侵地居群中检测到了杂交种的存在,这令我们推测在入侵地三裂叶豚草与姐妹种之间的杂交更为频繁,可能给进化提供了更丰富的遗传资源。2.转录组反映了在特定基因型中表达的全部活性基因。我们以三裂叶豚草为研究对象,尝试了用转录组测序的方法来研究该物种原产地和入侵地种质在基因表达方面的差异。我们使用Roche/454 Titanium测序平台对三裂叶豚草不同产地基因型的转录组cDNA文库进行了测序,得到原产地基因型206,343和入侵地基因型238,943条EST序列,代表了目前最丰富的三裂叶豚草EST序列资源。通过MIRA和Cap3对序列拼接组装和对比,共得到三个数据集：原产地基因型和入侵地基因型共有序列数捌集,包含10000条序列；原产地基因型特有序列数据集和入侵地基因型特有序列数据集,分别包含7407和9001条序列。通过与拟南芥信息资源(TAIR)转录体数据库进行BLAST,我们从两基因型共有序列数据集中识别了6859个Unigene,原产地基因型特有序列数据集和入侵地基因型特有序列数据集分别识别了3332和4174个Unigene。将Unigene输出结果进行Gene Ontology(GO)注释,每个数据集中都有约80%的基因通过功能注释得到了其涉及分子功能、生物过程以及细胞组分的信息。这些信息可以用于进一步研究与三裂叶豚草入侵能力相关的具体基因及分子机制。3.我们以白花蝇子草(Silene latifolia)为材料,研究了表型差异是否有遗传基础和造成差异的原因。我们对来自原产地欧洲和来自入侵地美国的3个在花朵大小上表现出性二态差异的居群进行了种内杂交,通过分析种内杂交后代的数量遗传参数,我们得知所研究的白花蝇子草的三个居群在花萼宽度均值和雌雄分异的程度上都表现出高度的可遗传性差异。QST值显示72.6%(雄性)和6.9%(雌性)的表型差异是由居群间差异造成的。入侵地和原产地之间的QST/FST比值对雄性是4.2而对雌性仅为0.40。该结果表明自然选择作用于雄性而不是雌性,造成了花萼宽度和其性二态程度的居群间表型差异,并为该种该性状发生了适应性分异提供了证据。更多还原

【Abstract】 Introduced species often have the potential to change relatively fast when encountering new environments. Those species that establish, reproduce and distribute successfully and become invasive in the introduced habitats usually experience adaptive evolution to the invaded land. Hence, invasive species are very suitable systems to study species differentiation and local adaptation. Research on the differentiation and adaptation mechanisms of invasive species would be beneficial to understand the phenomena of biological invasions and may help in management attempts.For this study, two invasive weed species were chosen as materials. We collected seeds from their natural populations of both native and introduced land. The differentiation of progenies from different regions was investigated at phenotypic and genetic levels, using ecological, quantitative genetic and genomic approaches. The quantitative genetic approach was also applied to evaluate whether genetic differentiation is caused by drift or natural selection. Possible adaptive mechanisms of the study species to the invaded regions were discussed. The study was composed by the following three parts.1. Phenotypic differentiation was studied in Ambrosia trifida. Experimental populations of progenies from its native populations in US and invasive population in China were grown in a greenhouse common environment. We compared the maternal seed traits, growth and reproductive traits of the experimental plants as well as their nuclear DNA content and responses to water, nutrition and simulated herbivory stresses. The results show that the plants from invaded region received significantly less infestation and may benefit from enemy release. The experimental plants from invasive region grew taller and slimmer at early stages compared to their native region counterparts, but the shape difference disappeared at later stages. This resource allocation pattern may be advantageous for invasive plants to compete against companion species for sunlight and space at early growth stage. Besides, invasive plants reproduced much earlier than native plants in the experiments. This highly significant difference implies that invasive plants of this species have evolved towards shorter life cycles compared to native plants. In the stress-related experiments, native plants and invasive plants showed similar growth and reproductive responses to drought and poor soil. However, growth and reproduction were reduced more in invasive plants than in native plants, which fact lends support to the EICA hypothesis. Meanwhile, compared to native plants the invasive plants exhibited greater phenotypic plasticity in terms of growth performance to maintain a certain level of reproductive performance under stresses and can maximize reproductive performance under better conditions. We suggest that enhanced phenotypic plasticity may have contributed positively to the invasive abilities of invasive genotypes. In addition, hybrids were detected in our sample of invasive plants but not in native plants, so we suspect hybridization of A. trifida with sister species is more frequent in the invaded region. This might provide richer genetic variation for natural selection to act on in the invaded region.2. Transcriptome reflects all the actively expressed genes in a given genotype. To investigate the genetic differentiation between a native genotype and an invasive genotype of A. trifida, we performed de novo transcriptome sequencing of the two genotypes. Roche/454 Titanium platform was used to sequence the cDNA libraries. The results include 206,343 reads from the native genotype and 238,943 reads from the invasive genotype. Through MIRA and Cap3 assembly we got 3 datasets:10,000 native and invasive genotype shared sequences,7,407 native genotype specific sequences and 9,001 invasive genotype specific sequences, which represents the best description of transcriptome of this species currently available. By BLAST against TAIR transcripts dataset, we recognized 6,859 Unigenes from the shared sequence dataset,3,332 and 4,174 Unigenes from the native genotype specific sequence dataset and invasive specific sequence dataset, respectively. Gene Ontology annotation was performed for each group, and around 80% genes were annotated in each group by biological process, cellular component or molecular function. The information would be used to further study the specific genes related to invasive ability of this species and the underlying molecular mechanisms.3. Whether phenotypic variation has a genetic basis and the cause is drift or selection was investigated in flower-size sexual dimorphism of Silene latifolia. Diallel crossing design was made using progenies from an invasive population in US and two native populations in Europe. By comparing the quantitative genetic parameters calculated from cross offspring phenotypes, we infer that the three populations exhibit highly heritable difference in both calyx width and sexual dimorphism of this trait. QST estimates revealed that 72.6%(males) versus 6.9%(females) of the phenotypic variation arises from differences among populations. The between-range QST/FST ratio was 4.2 for males versus 0.40 for females, suggesting that selection has acted on males but not females, and is responsible for phenotypic differentiation among populations in calyx width and its degree of sexual dimorphism. The result provides evidence for adaptive divergence for the study traits in the species instead of random phenotypic evolution.更多还原