The ability to follow the evolutionary trajectories of specific neuronal cell types has led to major insights into the evolution of the vertebrate brain. Here, we study how cave life in the Mexican tetra ( Astyanax mexicanus ) has affected an identified giant multisensory neuron, the Mauthner neuron (MN). Because this neuron is crucial in driving rapid escapes, the absence of predation risk in the cave forms predicts a massive reduction in this neuron. Moreover, the absence of functional eyes in the A. mexicanus Pachón form predicts an even stronger reduction in the cell’s large ventral dendrite that receives visual inputs in sighted fish species. We succeeded in recording in vivo from this neuron in the blind cavefish and two surface tetra ( A. mexicanus and Astyanax aeneus ), which offers unique chances to simultaneously study evolutionary changes in morphology and function in this giant neuron. In contrast to the predictions, we find that cave life, while sufficient to remove vision, has neither affected the cell's morphology nor its functional properties. This specifically includes the cell's ventral dendrite. Furthermore, cave life did not increase the variance in morphological or functional features. Rather, variability in surface and cave forms was the same, which suggests a complex stabilizing selection in this neuron and a continued role of its ventral dendrite. We found that adult cavefish are potent predators that readily attack smaller fish. So, one of the largely unknown stabilizing factors could be using the MN in such attacks and, in the young fish, escaping them.

中文翻译：

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稳定盲洞鱼中已鉴定的多感官神经元的选择


追踪特定神经元细胞类型进化轨迹的能力使人们对脊椎动物大脑的进化有了重大见解。在这里，我们研究了墨西哥四体鱼 （ Astyanax mexicanus ） 的洞穴生物如何影响已识别的巨大多感官神经元 Mauthner 神经元 （MN）。因为这个神经元在驱动快速逃跑方面至关重要，所以洞穴形式中没有捕食风险预示着这个神经元的大幅减少。此外，A. mexicanus Pachón 形式中没有功能性眼睛，这预示着细胞的大腹侧树突会更强烈地减少，该树突在视力鱼类中接收视觉输入。我们成功地在盲洞鱼和两个表面四体鱼（A. mexicanus 和 Astyanax aeneus）中记录了这个神经元的体内数据，这为同时研究这个巨大神经元的形态和功能的进化变化提供了独特的机会。与预测相反，我们发现洞穴生活虽然足以消除视力，但既不影响细胞的形态，也不会影响其功能特性。这特别包括细胞的腹侧树突。此外，洞穴生活并没有增加形态或功能特征的方差。相反，表面和洞穴形式的变异性是相同的，这表明该神经元中存在复杂的稳定选择，并且其腹侧树突的持续作用。我们发现成年洞穴鱼是强大的捕食者，很容易攻击较小的鱼。因此，一个基本未知的稳定因素可能是在此类攻击中使用 MN，并在幼鱼中逃脱它们。