No effect of ploidy level in plant response to competition in a common garden experiment

One of the important aspects explaining the evolutionary success of polyploid plants is that polyploids often, although not always, occupy a wider range of environments than their diploid ancestors. The two most likely explanations for this pattern are a wider plasticity in polyploid species and the existence of a range of locally adapted types. Most studies on patterns of distribution of different ploidy levels are only observational, and do not distinguish between these alternative explanations. The present study investigated the performance and plasticity of diploid and hexaploid cytotypes of a perennial plant, Aster amellus. The hexaploid plants occur in habitats with a wider range of competition intensity. Nine different populations of the species were selected: three diploid (from low competition habitats) and six hexaploid (from both low and high competition habitats). Plants were grown from seeds from these populations with and without competition in a common garden. Competition had strong effect on plant performance. There was, however, little effect of the ploidy levels and home environment. There was also almost no interaction between competition and ploidy level/home environment. The results of this study provide no support for any of the two suggested explanations for the wider range of habitats occupied by hexaploid plants. Other explanations thus must be thought. Generally, the results indicate that, although the higher plasticity of higher ploidy levels is often suggested, this may not be true. We therefore should attempt to assemble more experimental data to support or reject this assumption. (C) 2007 The Linnean Society of London.