Department of Biology, Center for Conservation Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway.
Evolution. 2010 Jul;64(7):1912-25. doi: 10.1111/j.1558-5646.2010.00979.x. Epub 2010 Feb 19.
How variation and variability (the capacity to vary) may respond to selection remain open questions. Indeed, effects of different selection regimes on variational properties, such as canalization and developmental stability are under debate. We analyzed the patterns of among- and within-individual variation in two wing-shape characters in populations of Drosophila melanogaster maintained under fluctuating, disruptive, and stabilizing selection for more than 20 generations. Patterns of variation in wing size, which was not a direct target of selection, were also analyzed. Disruptive selection dramatically increased phenotypic variation in the two shape characters, but left phenotypic variation in wing size unaltered. Fluctuating and stabilizing selection consistently decreased phenotypic variation in all traits. In contrast, within-individual variation, measured by the level of fluctuating asymmetry, increased for all traits under all selection regimes. These results suggest that canalization and developmental stability are evolvable and presumably controlled by different underlying genetic mechanisms, but the evolutionary responses are not consistent with an adaptive response to selection on variation. Selection also affected patterns of directional asymmetry, although inconsistently across traits and treatments.
变异和变异性（变异的能力）如何对选择产生响应仍然是悬而未决的问题。实际上，不同选择机制对变异特征（如 canalization 和发育稳定性）的影响仍存在争议。我们分析了在经过 20 多代的波动选择、破坏性选择和稳定选择后，果蝇（Drosophila melanogaster）种群中两个翅膀形状特征的个体间和个体内变异模式。我们还分析了翅膀大小的变异模式，翅膀大小不是选择的直接目标。破坏性选择显著增加了两个形状特征的表型变异，但对翅膀大小的表型变异没有影响。波动选择和稳定选择一致降低了所有特征的表型变异。相比之下，所有选择机制下，个体内变异（以波动不对称性的水平衡量）均增加。这些结果表明，canalization 和发育稳定性是可进化的，可能受不同的遗传机制控制，但进化响应与对变异的选择的适应性响应不一致。选择还影响了定向不对称性的模式，尽管在不同的特征和处理之间不一致。
