Department of Ecology and Evolutionary Biology, University of California, Irvine, California 92697, USA.
Am Nat. 2007 Mar;169(3):298-310. doi: 10.1086/510758. Epub 2007 Jan 24.
Interspecific hybridization is a recurring aspect of the evolution of many plant and animal groups. The temporal dynamics of hybrid zones and the evolutionary consequences of hybridization should depend on fitness of parental and hybrid individuals expressed in different environments. We measured lifetime fitness, including survival and reproduction, of plants of Ipomopsis aggregata, Ipomopsis tenuituba, and their F1 hybrids, in experimental plantings in a natural hybrid zone. Fitness, measured as the finite rate of increase ( lambda ), depended strongly on environment. Each parental species performed well in its home locale and poorly in the locale of the other species. Hybrids performed as well as parents overall but enjoyed their highest fitness in the hybrid site. Furthermore, F1 hybrids with I. tenuituba as maternal parent survived well only at the hybrid site, suggesting a cytonuclearxenvironment interaction. These results support an "environmental cline" model of hybrid zone dynamics, with complexities in the fitness of hybrids consistent also with an "evolutionary novelty" model. Combined with those of earlier studies of pollination, our results suggest that both vegetative adaptation to physical environment and floral adaptation to pollinators contribute to observed patterns of phenotypic expression in this hybrid zone and to persistence of the hybrid zone.
种间杂交是许多植物和动物群体进化过程中的一个反复出现的方面。杂种区的时间动态和杂交的进化后果应该取决于在不同环境中表现出的亲代和杂种个体的适合度。我们在自然杂种区的实验种植中测量了 Ipomopsis aggregata、Ipomopsis tenuituba 及其 F1 杂种的终生适合度，包括存活和繁殖。适合度，以有限增长率（λ）来衡量，强烈依赖于环境。每个亲本地种在其本地环境中表现良好，而在其他物种的环境中表现不佳。杂种总体上表现得与亲本地种一样好，但在杂种区中具有最高的适合度。此外，以 I. tenuituba 为母本的 F1 杂种仅在杂种区中生存良好，这表明存在胞质-核-环境相互作用。这些结果支持杂种区动态的“环境渐变”模型，杂种的适合度也存在复杂性，这与“进化新颖性”模型一致。结合早期授粉研究的结果，我们的研究结果表明，植物对物理环境的营养适应和花对传粉者的适应都有助于解释该杂种区中观察到的表型表达模式，并有助于杂种区的持续存在。
