Department of Botany, Faculty of Science, Charles University in Prague, Prague, Czech Republic.
PLoS One. 2012;7(7):e39988. doi: 10.1371/journal.pone.0039988. Epub 2012 Jul 5.
Polyploidization is one of the leading forces in the evolution of land plants, providing opportunities for instant speciation and rapid gain of evolutionary novelties. Highly selective conditions of serpentine environments act as an important evolutionary trigger that can be involved in various speciation processes. Whereas the significance of both edaphic speciation on serpentine and polyploidy is widely acknowledged in plant evolution, the links between polyploid evolution and serpentine differentiation have not yet been examined. To fill this gap, we investigated the evolutionary history of the perennial herb Knautia arvensis (Dipsacaceae), a diploid-tetraploid complex that exhibits an intriguing pattern of eco-geographic differentiation. Using plastid DNA sequencing and AFLP genotyping of 336 previously cytotyped individuals from 40 populations from central Europe, we unravelled the patterns of genetic variation among the cytotypes and the edaphic types. Diploids showed the highest levels of genetic differentiation, likely as a result of long term persistence of several lineages in ecologically distinct refugia and/or independent immigration. Recurrent polyploidization, recorded in one serpentine island, seems to have opened new possibilities for the local serpentine genotype. Unlike diploids, the serpentine tetraploids were able to escape from the serpentine refugium and spread further; this was also attributable to hybridization with the neighbouring non-serpentine tetraploid lineages. The spatiotemporal history of K. arvensis allows tracing the interplay of polyploid evolution and ecological divergence on serpentine, resulting in a complex evolutionary pattern. Isolated serpentine outcrops can act as evolutionary capacitors, preserving distinct karyological and genetic diversity. The serpentine lineages, however, may not represent evolutionary 'dead-ends' but rather dynamic systems with a potential to further influence the surrounding populations, e.g., via independent polyplodization and hybridization. The complex eco-geographical pattern together with the incidence of both primary and secondary diploid-tetraploid contact zones makes K. arvensis a unique system for addressing general questions of polyploid research.
多倍化是陆地植物进化的主要力量之一，为即时物种形成和快速获得进化创新提供了机会。蛇纹石环境的高度选择性条件充当了一个重要的进化触发因素，可参与各种物种形成过程。虽然蛇纹石土壤物种形成和多倍体在植物进化中的重要性已得到广泛认可，但多倍体进化与蛇纹石分化之间的联系尚未得到检验。为了填补这一空白，我们研究了多年生草本植物苣荬菜（川续断科）的进化历史，这是一个二倍体-四倍体复合体，表现出有趣的生态地理分化模式。使用质体 DNA 测序和 AFLP 基因型分析，对来自中欧 40 个种群的 336 个先前经过细胞型分类的个体进行分析，我们揭示了细胞型和土壤类型之间的遗传变异模式。二倍体表现出最高水平的遗传分化，这可能是由于几个谱系在生态上截然不同的避难所中长期存在，或者是由于独立的移民。在一个蛇纹石岛上记录的复发性多倍化似乎为当地蛇纹石基因型开辟了新的可能性。与二倍体不同，蛇纹石四倍体能够逃离蛇纹石避难所并进一步传播；这也归因于与邻近的非蛇纹石四倍体谱系的杂交。苣荬菜的时空历史允许追踪多倍体进化和生态分歧在蛇纹石上的相互作用，从而产生复杂的进化模式。孤立的蛇纹石露头可以作为进化电容器，保存独特的染色体和遗传多样性。然而，蛇纹石谱系可能不是进化的“死胡同”，而是具有进一步影响周围种群潜力的动态系统，例如，通过独立的多倍化和杂交。复杂的生态地理模式以及原发性和继发性二倍体-四倍体接触区的发生，使苣荬菜成为解决多倍体研究一般问题的独特系统。
