Lineages that have invaded subterranean environments have repeatedly evolved remarkable adaptations to life in darkness. However, observational and experimental studies in additional natural systems are needed to further our understanding of repeated evolution and convergence. In Texas, a radiation of groundwater salamanders (genus Eurycea ), with independent invasions of subterranean karstic environments, offers an opportunity to investigate phenotypic convergence, parallel evolution, and the enhancement and regression of sensory systems. Adaptations to a troglobitic life in this clade include morphological, behavioral, and physiological changes within and among species. Intraspecific and interspecific variation in morphology in response to the selective pressures of life underground allows for detailed examination of physical, behavioral, and physiological changes associated with subterranean adaptation within a comparative phylogenetic framework. We find a correlated change between two sensory systems repeated across multiple subterranean Eurycea lineages: the degeneration of the eye and the expansion of the mechanosensory lateral line. The increase in anterior neuromast organs in subterranean lineages was positively correlated with the expression of pax6 (Paired-box 6), a conserved transcription factor important for vertebrate neurogenesis. Our results show a decreasing trend of PAX6 labeling in the neuromasts of adult surface salamanders ( Eurycea nana ) relative to the maintained labeling in subterranean species ( Eurycea rathbuni ). These lateral line enhancements are correlated with reductions in the development of optic systems in subterranean salamander lineages. Altogether, our findings provide a starting point for future evolutionary developmental investigations examining the genetic underpinnings of adaptive, repeated evolution in a novel system.

中文翻译：

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地下水蝾螈 （ Eurycea ） 独立地下定植后的平行感觉补偿

侵入地下环境的谱系一再进化出对黑暗生活的非凡适应能力。然而，需要对其他自然系统进行观察和实验研究，以进一步理解重复进化和趋同。在德克萨斯州，地下水蝾螈（Eurycea 属）的辐射以及对地下喀斯特环境的独立入侵，为研究表型趋同、平行进化以及感觉系统的增强和回归提供了机会。该分支对穴居生活的适应包括物种内部和物种之间的形态、行为和生理变化。响应地下生命选择压力的形态学的种内和种间变化允许在比较系统发育框架内详细检查与地下适应相关的物理、行为和生理变化。我们发现在多个地下 Eurycea 谱系中重复的两个感觉系统之间存在相关变化：眼睛的退化和机械感觉侧线的扩张。地下谱系中前神经瘤器官的增加与 pax6 （Paired-box 6） 的表达呈正相关，pax6 是一种对脊椎动物神经发生很重要的保守转录因子。我们的结果表明，相对于地下物种 （Eurycea rathbuni） 中维持标记，成年表面蝾螈 （Eurycea nana） 神经丘中 PAX6 标记呈下降趋势。这些侧线增强与地下蝾螈谱系中光学系统发育的减少相关。 总而言之，我们的研究结果为未来的进化发育研究提供了一个起点，这些研究检查了新系统中适应性、重复进化的遗传基础。