Lambert Matthew J, Nevue Alexander A, Portfors Christine V
School of Biological Sciences, Washington State University Vancouver, United States.
School of Biological Sciences, Washington State University Vancouver, United States.
Gene. 2017 Mar 20;605:1-4. doi: 10.1016/j.gene.2016.12.017. Epub 2016 Dec 20.
Several recent studies have described genes demonstrating adaptive sequence convergence between echolocating bats and dolphin, suggesting that common selective pressures can induce common molecular changes, even in distantly related species. However, in the case of the auditory genes Otoferlin (Otof), Cadherin 23 (Cdh23) and Protocadherin 15 (Pcdh15), the reported sequence convergence was supported only by incongruent gene and species trees and counts of convergent substitutions. Therefore, it remains unclear whether echolocating bats and dolphin really do demonstrate evidence of adaptive sequence convergence, or whether there is simply a high level of random background convergence in these genes. To address this question, we estimated the number of convergent and divergent amino acid substitutions along all independent branches of a sufficiently deep phylogeny containing between 22 and 32 mammals for each gene, and compared convergence between the two proposed suborders of bat, Yangochiroptera and Yinpterochiroptera, and dolphin. We find no support for convergence between bats and dolphin in the gene Pcdh15. For the gene Otof we report minimal evidence for convergent evolution only between the Yinpterochiroptera and dolphin. Cdh23 displayed a high level of convergence between dolphin and the Yinpterochiroptera. In addition, dolphin and certain members of the Yangochiroptera that emit high frequency echolocation calls shared several unique convergent substitutions. These results indicate that the convergent evolution of Cdh23 was likely driven by selection for hearing above a certain frequency threshold. Moreover, the contrasting patterns of convergence between the two bat suborders and dolphin in all auditory genes studied thus far suggest echolocation may have evolved independently in the Yinpterochiroptera and Yangochiroptera.
最近的几项研究描述了一些基因，这些基因在回声定位蝙蝠和海豚之间表现出适应性序列趋同，这表明共同的选择压力可以诱导共同的分子变化，即使是在亲缘关系较远的物种中。然而，对于听觉基因 otoferlin（Otof）、钙黏蛋白 23（Cdh23）和原钙黏蛋白 15（Pcdh15）而言，所报道的序列趋同仅得到了不一致的基因和物种树以及趋同替换计数的支持。因此，目前尚不清楚回声定位蝙蝠和海豚是否真的表现出适应性序列趋同的证据，或者这些基因中是否仅仅存在高水平的随机背景趋同。为了解决这个问题，我们估计了在包含 22 至 32 种哺乳动物的足够深入的系统发育树中，每个基因沿所有独立分支的趋同和发散氨基酸替换的数量，并比较了蝙蝠的两个拟亚目（阳翼手亚目和阴翼手亚目）与海豚之间的趋同情况。我们发现 Pcdh15 基因在蝙蝠和海豚之间不存在趋同现象。对于 Otof 基因，我们仅报道了阴翼手亚目与海豚之间存在趋同进化的极少证据。Cdh23 在海豚和阴翼手亚目之间表现出高度趋同。此外，海豚与发出高频回声定位叫声的阳翼手亚目的某些成员共享了几个独特的趋同替换。这些结果表明，Cdh23 的趋同进化可能是由对高于特定频率阈值的听力选择驱动的。此外，到目前为止，在所有研究的听觉基因中，两个蝙蝠亚目与海豚之间不同的趋同模式表明，回声定位可能在阴翼手亚目和阳翼手亚目中独立进化。
