Charvet Christine J, Sandoval Alexis L, Striedter Georg F
Department of Neurobiology and Behavior and Center for the Neurobiology of Learning and Memory, University of California, Irvine, Irvine, Calif. 92687-4550, USA.
Brain Behav Evol. 2010;75(2):104-10. doi: 10.1159/000300573. Epub 2010 Mar 23.
Adult galliform birds (e.g. chickens) exhibit a relatively small telencephalon and a proportionately large optic tectum compared with parrots and songbirds. We previously examined the embryonic origins of these adult species differences and found that the optic tectum is larger in quail than in parakeets and songbirds at early stages of development, prior to tectal neurogenesis onset. The aim of this study was to determine whether a proportionately large presumptive tectum is a primitive condition within birds or a derived feature of quail and other galliform birds. To this end, we examined embryonic brains of several avian species (emus, parrots, songbirds, waterfowl, galliform birds), reptiles (3 lizard species, alligators, turtles) and a monotreme (platypuses). Brain region volumes were estimated from serial Nissl-stained sections. We found that the embryos of galliform birds and lizards exhibit a proportionally larger presumptive tectum than all the other examined species. The presumptive tectum of the platypus is unusually small. The most parsimonious interpretation of these data is that the expanded embryonic tectum of lizards and galliform birds is a derived feature in both of these taxonomic groups.
与鹦鹉和鸣禽相比，成年鸡形目鸟类（如鸡）的端脑相对较小，视顶盖相对较大。我们之前研究了这些成年物种差异的胚胎起源，发现在视顶盖神经发生开始之前的发育早期阶段，鹌鹑的视顶盖比长尾小鹦鹉和鸣禽的更大。本研究的目的是确定相对较大的假定视顶盖是鸟类的原始特征还是鹌鹑和其他鸡形目鸟类的衍生特征。为此，我们检查了几种鸟类（鸸鹋、鹦鹉、鸣禽、水禽、鸡形目鸟类）、爬行动物（3种蜥蜴、短吻鳄、海龟）和一种单孔目动物（鸭嘴兽）的胚胎大脑。通过对尼氏染色连续切片估计脑区体积。我们发现，鸡形目鸟类和蜥蜴的胚胎比所有其他检查物种的假定视顶盖比例更大。鸭嘴兽的假定视顶盖异常小。对这些数据最简洁的解释是，蜥蜴和鸡形目鸟类胚胎视顶盖的扩大是这两个分类群的衍生特征。
