Hoops Daniel, Vidal-García Marta, Ullmann Jeremy F P, Janke Andrew L, Stait-Gardner Timothy, Duchêne David A, Price William S, Whiting Martin J, Keogh J Scott
Division of Ecology and Evolution, Research School of Biology, The Australian National University, Acton, ACT, Australia.
Brain Behav Evol. 2017;90(3):211-223. doi: 10.1159/000478738. Epub 2017 Sep 5.
The brain plays a critical role in a wide variety of functions including behaviour, perception, motor control, and homeostatic maintenance. Each function can undergo different selective pressures over the course of evolution, and as selection acts on the outputs of brain function, it necessarily alters the structure of the brain. Two models have been proposed to explain the evolutionary patterns observed in brain morphology. The concerted brain evolution model posits that the brain evolves as a single unit and the evolution of different brain regions are coordinated. The mosaic brain evolution model posits that brain regions evolve independently of each other. It is now understood that both models are responsible for driving changes in brain morphology; however, which factors favour concerted or mosaic brain evolution is unclear. Here, we examined the volumes of the 6 major neural subdivisions across 14 species of the agamid lizard genus Ctenophorus (dragons). These species have diverged multiple times in behaviour, ecology, and body morphology, affording a unique opportunity to test neuroevolutionary models across species. We assigned each species to an ecomorph based on habitat use and refuge type, then used MRI to measure total and regional brain volume. We found evidence for both mosaic and concerted brain evolution in dragons: concerted brain evolution with respect to body size, and mosaic brain evolution with respect to ecomorph. Specifically, all brain subdivisions increase in volume relative to body size, yet the tectum and rhombencephalon also show opposite patterns of evolution with respect to ecomorph. Therefore, we find that both models of evolution are occurring simultaneously in the same structures in dragons, but are only detectable when examining particular drivers of selection. We show that the answer to the question of whether concerted or mosaic brain evolution is detected in a system can depend more on the type of selection measured than on the clade of animals studied.
大脑在包括行为、感知、运动控制和内稳态维持等多种功能中发挥着关键作用。在进化过程中，每种功能可能会经历不同的选择压力，并且由于选择作用于大脑功能的输出，它必然会改变大脑的结构。已经提出了两种模型来解释在脑形态学中观察到的进化模式。协同脑进化模型假定大脑作为一个单一单元进化，不同脑区的进化是协调的。镶嵌脑进化模型假定脑区彼此独立进化。现在人们明白，这两种模型都在推动脑形态的变化；然而，哪些因素有利于协同或镶嵌脑进化尚不清楚。在这里，我们研究了鬃狮蜥属（鬃狮蜥）14个物种的6个主要神经亚区的体积。这些物种在行为、生态和身体形态上已经多次分化，为跨物种测试神经进化模型提供了独特的机会。我们根据栖息地利用和避难所类型将每个物种归类为一种生态形态，然后使用磁共振成像来测量全脑和区域脑体积。我们在鬃狮蜥中发现了镶嵌和协同脑进化的证据：相对于体型的协同脑进化，以及相对于生态形态的镶嵌脑进化。具体来说，所有脑亚区的体积相对于体型都有所增加，但顶盖和后脑相对于生态形态也显示出相反的进化模式。因此，我们发现这两种进化模型在鬃狮蜥的相同结构中同时发生，但只有在研究特定的选择驱动因素时才能检测到。我们表明，在一个系统中检测到协同还是镶嵌脑进化的问题，答案可能更多地取决于所测量的选择类型，而不是所研究的动物类群。
