Jiangsu Key Laboratory for Biodiversity and Biotechnology, College of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, People's Republic of China.
Proc Biol Sci. 2012 Nov 7;279(1746):4433-40. doi: 10.1098/rspb.2012.1729. Epub 2012 Sep 12.
The enlargement of cetacean brain size represents an enigmatic event in mammalian evolution, yet its genetic basis remains poorly explored. One candidate gene associated with brain size evolution is the abnormal spindle-like microcephaly associated (ASPM), as mutations in this gene cause severe reductions in the cortical size of humans. Here, we investigated the ASPM gene in representative cetacean lineages and previously published sequences from other mammals to test whether the expansion of the cetacean brain matched adaptive ASPM evolution patterns. Our analyses yielded significant evidence of positive selection on the ASPM gene during cetacean evolution, especially for the Odontoceti and Delphinoidea lineages. These molecular patterns were associated with two major events of relative brain size enlargement in odontocetes and delphinoids. It is of particular interest to find that positive selection was restricted to cetaceans and primates, two distant lineages both characterized by a massive expansion of brain size. This result is suggestive of convergent molecular evolution, although no site-specific convergence at the amino acid level was found.
鲸类大脑尺寸的增大是哺乳动物进化中的一个谜，但它的遗传基础仍未得到充分探索。与大脑尺寸进化相关的一个候选基因是异常纺锤状微脑症相关（ASPM），因为该基因的突变会导致人类皮质尺寸严重减小。在这里，我们研究了代表性鲸类谱系中的 ASPM 基因和其他哺乳动物已发表的序列，以测试鲸类大脑的扩大是否符合适应性 ASPM 进化模式。我们的分析为 ASPM 基因在鲸类进化过程中提供了显著的正选择证据，尤其是在齿鲸和海豚类群中。这些分子模式与齿鲸和海豚中相对大脑尺寸增大的两个主要事件相关。有趣的是，正选择仅限于鲸类和灵长类动物，这两个远缘谱系的大脑尺寸都有大量的扩张。这一结果表明存在趋同的分子进化，尽管在氨基酸水平上没有发现特定的趋同。
