Labbé Pierrick, Sidos Nicolas, Raymond Michel, Lenormand Thomas
Université de Montpellier, Montpellier Cedex 4, France.
Genetics. 2009 May;182(1):303-12. doi: 10.1534/genetics.109.101444. Epub 2009 Mar 16.
How adaptation appears and is later refined by natural selection has been the object of intense theoretical work. However, the testing of these theories is limited by our ability to estimate the strength of natural selection in nature. Using a long-term cline series, we estimate the selection coefficients acting on different alleles at the same locus to analyze the allele replacement observed in the insecticide resistance gene Ester in the mosquito Culex pipiens in the Montpellier area, southern France. Our method allows us to accurately account for the resistance allele replacement observed in this area since 1986. A first resistance allele appeared early, which was replaced by a second resistance allele providing the same advantage but at a lower cost, itself being replaced by a third resistance allele with both higher advantage and cost. It shows that amelioration of the adaptation (here resistance to insecticide) through allele replacement was successively achieved by selection of first a generalist allele (i.e., with a low fitness variance across environments) and later a specialist allele (i.e., with a large fitness variance across environments). More generally, we discuss how precise estimates of the strength of selection obtained from field data help us understand the process of amelioration of adaptation.
适应如何出现以及随后如何通过自然选择得到优化，一直是大量理论研究的对象。然而，这些理论的验证受到我们估计自然选择在自然界中强度能力的限制。利用一个长期渐变系列，我们估计了作用于同一基因座不同等位基因的选择系数，以分析在法国南部蒙彼利埃地区淡色库蚊抗杀虫剂基因Ester中观察到的等位基因替代情况。我们的方法使我们能够准确解释自1986年以来在该地区观察到的抗性等位基因替代现象。第一个抗性等位基因出现得较早，随后被第二个抗性等位基因取代，第二个等位基因具有相同的优势，但成本较低，而它本身又被第三个具有更高优势和成本的抗性等位基因所取代。这表明，通过等位基因替代实现的适应性改善（这里指对杀虫剂的抗性）先是通过选择一个泛化等位基因（即在不同环境中适应性方差较低），随后又通过选择一个特化等位基因（即在不同环境中适应性方差较大）得以相继实现。更一般地说，我们讨论了从实地数据获得的选择强度的精确估计如何帮助我们理解适应性改善的过程。
