Barrett Rowan D H, Bell Graham
Department of Biology, McGill University, Montreal, Quebec, Canada.
Evolution. 2006 Mar;60(3):484-90.
Determining the mechanisms that promote the evolution of diversity is a central problem in evolutionary biology. Previous studies have demonstrated that diversification occurs in complex environments and that genotypes specialized on alternative resources can be maintained over short time scales. Here, we describe a selection experiment that has tracked the dynamics of adaptive diversification within selection lines of the asexual bacteria Pseudomonas fluorescens over about 900 generations. We cultured experimental populations from the same two isogenic ancestral strains in simple, single-substrate environments or in complex, four-substrate environments. Following selection we assayed the growth of genotypes from each population on each substrate individually. We estimated mutational heritability, Vm/VE, as 1 x 10(-3) per generation in simple environments and 3 x 10(-3) per generation in complex environments. These values are roughly consistent with estimates reported in other systems. Populations selected in complex environments evolved into genetically diverse communities. Genotypes exhibited greater metabolic differentiation from other genotypes in their own population than to genotypes evolving in other populations, presumably as a result of resource competition. In populations selected in simple environments, little genetic diversity evolved, and genotypes shared very similar phenotypes. Our findings suggest that ecological opportunity provided by environmental complexity plays a major role in the evolution and maintenance of diversity.
确定促进多样性进化的机制是进化生物学的核心问题。先前的研究表明，多样化发生在复杂环境中，并且专门利用替代资源的基因型可以在短时间尺度上得以维持。在此，我们描述了一项选择实验，该实验追踪了无性细菌荧光假单胞菌选择系中适应性多样化的动态变化，历时约900代。我们从相同的两个同基因祖先菌株在简单的单底物环境或复杂的四底物环境中培养实验群体。经过选择后，我们分别测定了每个群体中基因型在每种底物上的生长情况。我们估计在简单环境中每代的突变遗传力Vm/VE为1×10⁻³，在复杂环境中为3×10⁻³每代。这些值与其他系统中报道的估计值大致一致。在复杂环境中选择的群体进化成遗传上多样化的群落。与自身群体中的其他基因型相比，基因型在代谢上与其他群体中进化的基因型表现出更大的差异，这可能是资源竞争的结果。在简单环境中选择的群体中几乎没有进化出遗传多样性, 并且基因型具有非常相似 的表型。我们 的研究结果表明，环境复杂性提供 的生态机会在多样性 的进化和维持中起主要作用。
