School of Biological Sciences, Washington State University, Pullman, Washington, United States of America.
PLoS One. 2012;7(9):e44928. doi: 10.1371/journal.pone.0044928. Epub 2012 Sep 27.
The ASPM (abnormal spindle-like microcephaly associated) gene has been proposed as a major determinant of cerebral cortical size among primates, including humans. Yet the specific functions of ASPM and its connection to human intelligence remain controversial. This debate is limited in part by a taxonomic focus on Old World monkeys and apes. Here we expand the comparative context of ASPM sequence analyses with a study of New World monkeys, a radiation of primates in which enlarged brain size has evolved in parallel in spider monkeys (genus Ateles) and capuchins (genus Cebus). The primate community of Costa Rica is perhaps a model system because it allows for independent pairwise comparisons of smaller- and larger-brained species within two taxonomic families. Accordingly, we analyzed the complete sequence of exon 18 of ASPM in Ateles geoffroyi, Alouatta palliata, Cebus capucinus, and Saimiri oerstedii. As the analysis of multiple species in a genus improves phylogenetic reconstruction, we also analyzed eleven published sequences from other New World monkeys. Our exon-wide, lineage-specific analysis of eleven genera and the ratio of rates of nonsynonymous to synonymous substitutions (d(N)/d(S)) on ASPM revealed no detectable evidence for positive selection in the lineages leading to Ateles or Cebus, as indicated by d(N)/d(S) ratios of <1.0 (0.6502 and 0.4268, respectively). Our results suggest that a multitude of interacting genes have driven the evolution of larger brains among primates, with different genes involved in this process in different encephalized lineages, or at least with evidence for positive selection not readily apparent for the same genes in all lineages. The primate community of Costa Rica may serve as a model system for future studies that aim to elucidate the molecular mechanisms underlying cognitive capacity and cortical size.
ASPM（异常纺锤体微小头相关）基因被认为是灵长类动物，包括人类大脑皮层大小的主要决定因素。然而，ASPM 的具体功能及其与人类智力的联系仍然存在争议。这种争论部分受到旧世界猴子和猿类分类学焦点的限制。在这里，我们通过对新世界猴子的研究扩展了 ASPM 序列分析的比较背景，新世界猴子是灵长类动物的一个辐射分支，在蜘蛛猴（属 Ateles）和卷尾猴（属 Cebus）中，大脑大小的扩大是平行进化的。哥斯达黎加的灵长类动物群体可能是一个模型系统，因为它允许在两个分类家族中对较小和较大脑型的物种进行独立的成对比较。因此，我们分析了阿特拉斯 Geoffroyi、白脸卷尾猴、白脸卷尾猴和 Saimiri oerstedii 中 ASPM 外显子 18 的完整序列。由于在一个属中分析多个物种可以提高系统发育重建的准确性，我们还分析了来自其他新世界猴子的 11 个已发表的序列。我们对 11 个属的外显子广泛的谱系特异性分析以及 ASPM 上非同义替换与同义替换的比率（d（N）/d（S））表明，在导致阿特拉斯或卷尾猴的谱系中没有检测到正选择的证据，d（N）/d（S）比率<1.0（分别为 0.6502 和 0.4268）。我们的结果表明，许多相互作用的基因驱动了灵长类动物大脑的进化，不同的基因在不同的脑化谱系中参与了这个过程，或者至少在所有谱系中，相同基因的正选择证据并不明显。哥斯达黎加的灵长类动物群体可能成为未来研究的模型系统，旨在阐明认知能力和皮层大小的分子机制。
