Institute of Neuroscience, University of Oregon, Eugene, Oregon 97403, USA.
Evolution. 2012 Feb;66(2):419-34. doi: 10.1111/j.1558-5646.2011.01441.x. Epub 2011 Sep 25.
Evolution of similar phenotypes in independent populations is often taken as evidence of adaptation to the same fitness optimum. However, the genetic architecture of traits might cause evolution to proceed more often toward particular phenotypes, and less often toward others, independently of the adaptive value of the traits. Freshwater populations of Alaskan threespine stickleback have repeatedly evolved the same distinctive opercle shape after divergence from an oceanic ancestor. Here we demonstrate that this pattern of parallel evolution is widespread, distinguishing oceanic and freshwater populations across the Pacific Coast of North America and Iceland. We test whether this parallel evolution reflects genetic bias by estimating the additive genetic variance-covariance matrix (G) of opercle shape in an Alaskan oceanic (putative ancestral) population. We find significant additive genetic variance for opercle shape and that G has the potential to be biasing, because of the existence of regions of phenotypic space with low additive genetic variation. However, evolution did not occur along major eigenvectors of G, rather it occurred repeatedly in the same directions of high evolvability. We conclude that the parallel opercle evolution is most likely due to selection during adaptation to freshwater habitats, rather than due to biasing effects of opercle genetic architecture.
独立群体中相似表型的进化通常被视为对相同适应最优值的适应证据。然而，性状的遗传结构可能导致进化更频繁地朝着特定的表型发展，而不是朝着其他表型发展，而与性状的适应性价值无关。阿拉斯加三刺鱼的淡水种群在与海洋祖先分离后，多次进化出相同的独特的鳃盖形状。在这里，我们证明了这种平行进化的模式是广泛存在的，它区分了北美的太平洋沿岸和冰岛的海洋和淡水种群。我们通过估计阿拉斯加海洋（假定的祖先）种群中鳃盖形状的加性遗传方差-协方差矩阵 (G) 来检验这种平行进化是否反映了遗传偏差。我们发现鳃盖形状的加性遗传方差显著，并且由于存在具有低加性遗传变异的表型空间区域，G 具有产生偏差的潜力。然而，进化并没有沿着 G 的主要特征向量发生，而是在相同的高可进化性方向上反复发生。我们的结论是，平行的鳃盖进化最有可能是由于对淡水生境的适应选择，而不是由于鳃盖遗传结构的偏差效应。
