Department of Zoology, Stockholm University, Stockholm, Sweden.
Department of Mathematics, Uppsala University, Uppsala, Sweden.
Evolution. 2017 Dec;71(12):2942-2951. doi: 10.1111/evo.13373. Epub 2017 Nov 13.
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 microcomputer tomography to investigate how the volumes of 11 main brain regions respond to selection for larger versus 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.
脊椎动物的大脑在分类上表现出高度的保守性。然而，不同物种之间的单独脑区的相对大小差异显著。一个有趣的模式是，较大的大脑似乎只与特定脑区（例如大脑皮层和小脑）的相对大小的增加有关。到目前为止，单独脑区与大脑整体大小之间的进化关联是基于比较证据，尚未经过实验验证。在这里，我们在为相对大脑大小较大和较小而选择的孔雀鱼（Poecilia reticulata）中测试了脑区对大脑大小的定向选择的进化反应。在这些动物中，人工选择导致相对大脑大小的快速响应，而身体大小保持不变。我们使用微机断层扫描来研究 11 个主要脑区的体积如何对大脑大小的选择产生反应。我们发现大脑区的相对体积在大、小脑动物之间没有差异，只有轻微的性别特异性变化。此外，选择并没有改变大脑和脑区大小之间的异速缩放关系。我们的研究结果表明，脑区对相对大脑大小的强烈定向选择的反应相似，这表明当代物种的大脑解剖结构的变化很可能源于对关键区域的直接选择。
