Data from: Hybridization and invasion: an experimental test with diffuse knapweed (Centaurea diffusa Lam.)

A number of studies have suggested a link between hybridization and invasion. In this study, we experimentally test the potential for hybridization to influence invasion through a greenhouse common garden study. Diffuse knapweed (Centaurea diffusa Lam.) was introduced to North America with admixture from spotted knapweed (Centaurea stoebe subsp. stoebe L.). Comparisons between North American diffuse knapweed (including hybrid phenotypes) and native (European) diffuse knapweed in a common garden did not reveal enhanced performance or increased phenotypic variance, suggesting that pre-introduction hybridization or, more generally, post-introduction evolutionary change, has not significantly contributed to the invasion of diffuse knapweed. In contrast, early generation hybrids [artificially created Back Cross 1 (BC1) plants] exhibited increased variance for eight of the examined traits, and greater leaf and reproductive shoot production when compared to North American diffuse knapweed. Individual BC1 lines differed for several traits, suggesting the importance of the cross for drawing conclusions from such comparisons. When compared to the parental species (diffuse and spotted knapweed), the BC1 plants were not transgressive for any of the measured traits. Overall, these findings suggest that if diploid spotted knapweed is introduced to North America, interspecific hybridization has the potential to result in even more aggressive invaders.多项研究均表明杂交与生物入侵（biological invasion）之间存在关联。本研究通过温室同质园实验（common garden experiment），对杂交作用于生物入侵的潜在可能性开展了实验验证。扩散矢车菊（*Centaurea diffusa* Lam.）被引入北美后，与斑点矢车菊（*Centaurea stoebe* subsp. *stoebe* L.）发生了杂交混合。在同质园实验中，对北美扩散矢车菊（包含杂交表型）与原生（欧洲）扩散矢车菊进行比较后，未发现前者生长表现更优或表型方差（phenotypic variance）更高，这表明引入前的杂交，或更宽泛地说，引入后的演化改变，并未对扩散矢车菊的入侵过程起到显著促进作用。与之相反，早期世代杂交种[人工构建的回交一代（Back Cross 1, BC1）植株]在8个检测性状中均表现出更高的表型方差，且相较于北美扩散矢车菊，其叶片与生殖枝的生成量更高。单个BC1株系在多个性状上存在差异，这表明该杂交组合在基于此类比较推导结论时具有重要意义。当与亲本物种（扩散矢车菊与斑点矢车菊）进行比较时，BC1植株在所有检测性状上均未表现出超亲现象。综合来看，本研究结果表明，若将二倍体（diploid）斑点矢车菊引入北美，种间杂交（interspecific hybridization）有可能培育出入侵性更强的物种。