Data from: Evolution of brain region volumes during artificial selection for relative brain size

The vertebrate brain shows an extremely conserved layout across taxa. Still, the relative sizes of separate brain regions vary markedly between species. One interesting pattern is that larger brains seem associated with increased relative sizes only of certain brain regions, for instance telencephalon and cerebellum. Till now, the evolutionary association between separate brain regions and overall brain size is based on comparative evidence and remains experimentally untested. Here we test the evolutionary response of brain regions to directional selection on brain size in guppies (Poecilia reticulata) selected for large and small relative brain size. In these animals, artificial selection led to a fast response in relative brain size, while body size remained unchanged. We use micro-CT to investigate how the volumes of 11 main brain regions respond to selection for larger vs. smaller brains. We found no differences in relative brain region volumes between large- and small-brained animals and only minor sex-specific variation. Also, selection did not change allometric scaling between brain and brain region sizes. Our results suggest that brain regions respond similarly to strong directional selection on relative brain size, which indicates that brain anatomy variation in contemporary species most likely stem from direct selection on key regions.脊椎动物大脑（vertebrate brain）在各分类类群中呈现出高度保守的解剖布局。尽管如此，不同物种间各脑区的相对体积仍存在显著差异。其中一个有趣的演化模式是：大脑总体积更大的物种，仅特定脑区的相对体积会随之增大，例如端脑（telencephalon）与小脑（cerebellum）。迄今为止，不同脑区与总体脑体积之间的演化关联仅依托比较生物学证据，尚未得到实验验证。本研究以经过相对脑体积大小选育的孔雀鱼（Poecilia reticulata）为实验对象，探究脑区对脑体积定向选择的演化响应。在该实验对象中，人工选择可快速改变其相对脑体积，而躯体体积则保持稳定。我们借助显微计算机断层扫描（micro-CT）技术，分析11个主要脑区的体积如何响应脑体积增大或减小的选择压力。研究结果显示，高脑体积与低脑体积品系的个体间，各脑区的相对体积并无显著差异，仅存在细微的性别特异性变异。此外，定向选择并未改变总体脑体积与各脑区体积之间的异速生长缩放（allometric scaling）关系。本研究结果表明，各脑区对相对脑体积的强定向选择响应模式一致，这意味着现生物种的脑解剖结构差异，大概率源自关键脑区受到的直接选择压力。