Geographical variables of invasive Mikania micrantha populations

Why invasive species can rapidly adapt to novel environments
is a puzzling question known
as the genetic paradox of invasive species. This
paradox is explainable in
terms of transposable elements (TEs) activity,
which are theorized to be powerful mutational
forces to create genetic variation. Mikania
micrantha, a noxious invasive weed, in this
sense provides an excellent opportunity
to test the explanation. The genetic
and epigenetic variation of 21 invasive populations
of M. micrantha in southern
China have been examined by using Transposon DisplayTD) and Transposon Methylation Display (TMD) techniques to survey 12 TE superfamilies. Our results showed that M. micrantha populations maintained an almost equally high level of TE-based genetic and epigenetic variation and they have been differentiated into subpopulations genetically and epigenetically. A similar positive spatial genetic and epigenetic structure pattern was observed within 300 m. Six and seven TE superfamilies presented significant genetic and epigenetic isolation by distance (IBD) pattern. In total, 59 genetic and 86 epigenetic adaptive TE loci were identified. Of them, 51 genetic and 44 epigenetic loci were found to correlate with 25 environmental variables (including precipitation, temperature, vegetation coverage, and soil metals). Twenty-five transposon-inserted genes were sequenced and homology-based annotated, which are found to be involved in a variety of molecular and cellular functions. Our research consolidates the importance of TE-associated genetic and epigenetic variation in the rapid adaptation and invasion of M. micrantha.

为何入侵物种能够快速适应全新环境，是一个被称为“入侵物种遗传悖论”的难解谜题。这一悖论可通过转座因子（transposable elements, TEs）的活性加以解释——这类因子被认为是催生遗传变异的强效突变力量。在该研究背景下，有害入侵杂草薇甘菊（Mikania micrantha）为验证该解释提供了绝佳的实验契机。研究人员采用转座子展示（Transposon Display, TD）与转座子甲基化展示（Transposon Methylation Display, TMD）技术，对中国南部21个薇甘菊入侵种群开展遗传与表观遗传变异分析，共调查了12个转座因子超家族。结果显示，薇甘菊种群维持着近乎同等高水平的基于转座因子的遗传与表观遗传变异，且已在遗传与表观遗传层面分化出亚种群。在300米范围内，研究人员观察到了相似的正向空间遗传与表观遗传结构模式。共有6个与7个转座因子超家族分别呈现出显著的距离隔离（isolation by distance, IBD）遗传与表观遗传模式。总计鉴定出59个遗传层面与86个表观遗传层面的适应性转座因子位点。其中，51个遗传位点与44个表观遗传位点分别与25项环境变量显著相关，包括降水量、温度、植被覆盖率以及土壤金属含量。研究人员对25个转座子插入基因进行了测序并完成基于同源性的注释，发现这些基因参与了多种分子与细胞功能。本研究证实了与转座因子相关的遗传与表观遗传变异在薇甘菊快速适应与入侵过程中的重要性。