Maximino Caio
Laboratory of Psychobiology and Experimental Psychopatology, Department of Psychology, Universidade Estadual Paulista, Bauru, Brazil.
PLoS One. 2008;3(10):e3582. doi: 10.1371/journal.pone.0003582. Epub 2008 Oct 30.
The tectum is a structure localized in the roof of the midbrain in vertebrates, and is taken to be highly conserved in evolution. The present article assessed three hypotheses concerning the evolution of lamination and citoarchitecture of the tectum of nontetrapod animals: 1) There is a significant degree of phylogenetic inertia in both traits studied (number of cellular layers and number of cell classes in tectum); 2) Both traits are positively correlated accross evolution after correction for phylogeny; and 3) Different developmental pathways should generate different patterns of lamination and cytoarchitecture.
METHODOLOGY/PRINCIPAL FINDINGS: The hypotheses were tested using analytical-computational tools for phylogenetic hypothesis testing. Both traits presented a considerably large phylogenetic signal and were positively associated. However, no difference was found between two clades classified as per the general developmental pathways of their brains.
CONCLUSIONS/SIGNIFICANCE: The evidence amassed points to more variation in the tectum than would be expected by phylogeny in three species from the taxa analysed; this variation is not better explained by differences in the main course of development, as would be predicted by the developmental clade hypothesis. Those findings shed new light on the evolution of an functionally important structure in nontetrapods, the most basal radiations of vertebrates.
中脑顶盖是脊椎动物中脑顶部的一个结构，被认为在进化过程中高度保守。本文评估了关于非四足动物顶盖分层和细胞结构进化的三个假说：1）在所研究的两个特征（顶盖中的细胞层数和细胞类别数）中存在显著程度的系统发育惯性；2）在对系统发育进行校正后，这两个特征在整个进化过程中呈正相关；3）不同的发育途径应产生不同的分层和细胞结构模式。
方法/主要发现：使用用于系统发育假设检验的分析计算工具对这些假说进行了检验。这两个特征都呈现出相当大的系统发育信号且呈正相关。然而，根据其大脑的一般发育途径分类的两个进化枝之间未发现差异。
结论/意义：所积累的证据表明，在所分析的分类群中的三个物种中，顶盖的变异比系统发育所预期的更多；这种变异不能像发育进化枝假说所预测的那样，通过发育主要过程的差异得到更好的解释。这些发现为非四足动物（脊椎动物最基部的类群）中一个功能重要结构 的进化提供了新的线索。
