Obbard Darren J, Harris Stephen A, Buggs Richard J A, Pannell John R
Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, United Kingdom.
Evolution. 2006 Sep;60(9):1801-15.
Hybridization and polyploidy are widely believed to be important sources of evolutionary novelty in plant evolution. Both can lead to novel gene combinations and/or novel patterns of gene expression, which in turn provide the variation on which natural selection can act. Here, we use nuclear and plastid gene trees, in conjunction with morphological data and genome size measurements, to show that both processes have been important in shaping the evolution of the angiosperm genus Mercurialis, particularly a clade of annual lineages that shows exceptional variation in the sexual system. Our results indicate that hexaploid populations of M. annua, in which the rare sexual system androdioecy is common (the occurrence of males and hermaphrodites) is of allopolyploid origin involving hybridization between an autotetraploid lineage of M. annua and the related diploid species M. huetii. We discuss the possibility that androdioecy may have evolved as a result of hybridization between dioecious M. huetii and monoecious tetraploid M. annua, an event that brought together the genes for specialist males with those for hermaphrodites.
杂交和多倍体被广泛认为是植物进化中进化新奇性的重要来源。两者都能导致新的基因组合和/或新的基因表达模式，进而提供自然选择可以作用的变异。在这里，我们结合核基因树和质体基因树，以及形态学数据和基因组大小测量，来表明这两个过程在塑造被子植物山靛属的进化中都很重要，特别是一年生谱系的一个分支，其性别系统表现出异常的变异。我们的结果表明，一年生山靛的六倍体种群，其中罕见的雄性两性花性别系统很常见（雄性和雌雄同体的出现），是异源多倍体起源，涉及一年生山靛的一个同源四倍体系与相关二倍体物种休氏山靛之间的杂交。我们讨论了雄性两性花性别系统可能是由于雌雄异株的休氏山靛与雌雄同株的四倍体一年生山靛杂交而进化而来的可能性，这一事件将专门化雄性的基因与雌雄同体的基因聚集在一起。
