The salamander clade Eurycea from the karst regions of central Texas provides an ideal platform for comparing divergent nervous and sensory systems since some species exhibit extreme phenotypes thought to be associated with inhabiting a subterranean environment, including highly reduced eyes, while others retain an ancestral ocular phenotype appropriate for life above ground. We describe ocular morphology, comparing three salamander species representing two phenotypes—the surface-dwelling Barton Springs salamander (E. sosorum) and San Marcos salamander (E. nana) and the obligate subterranean Texas blind salamander (E. rathbuni) - in terms of structure and size of their eyes. Eyes were examined using confocal microscopy and measurements were made using ImageJ. Statistical analysis of data was carried out using R. We also provide a developmental series and track eye development and immunolocalization of Pax6 in E. sosorum and E. rathbuni. Adult histology of the surface-dwelling San Marcos salamander (E. nana) shows similarities to E. sosorum. The eyes of adults of the epigean species E. nana and E. sosorum appear fully developed with all the histological features of a fully functional eye. In contrast, the eyes of E. rathbuni adults have fewer layers, lack lenses and other features associated with vision as has been reported previously. However, in early developmental stages eye morphology did not differ significantly between E. rathbuni and E. sosorum. Parallel development is observed between the two phenotypes in terms of morphology; however, Pax6 labeling seems to decrease in the latter stages of development in E.rathbuni. We test for immunolabeling of the visual pigment proteins opsin and rhodopsin and observe immunolocalization around photoreceptor disks in E. nana and E. sosorum, but not in the subterranean E. rathbuni. Our results from examining developing salamanders suggest a combination of underdevelopment and degeneration contribute to the reduced eyes of adult E. rathbuni.

中文翻译：

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德克萨斯州中部表层蝾螈和地下蝾螈（Eurycea）的比较发育和眼组织学


来自德克萨斯州中部喀斯特地区的蝾螈分支为比较不同的神经和感觉系统提供了一个理想的平台，因为一些物种表现出被认为与居住在地下环境有关的极端表型，包括高度缩小的眼睛，而其他物种则保留了祖先的眼睛表型适合地上生活。我们描述了眼睛形态，比较了代表两种表型的三种蝾螈物种——生活在地表的巴顿泉蝾螈（E. sosorum）和圣马科斯蝾螈（E. nana）以及专性地下德克萨斯盲蝾螈（E.rathbuni）——他们眼睛的结构和大小。使用共焦显微镜检查眼睛并使用 ImageJ 进行测量。使用 R 进行数据统计分析。我们还提供发育系列并跟踪 E. sosorum 和 E. rathbuni 中 Pax6 的眼睛发育和免疫定位。地表圣马科斯蝾螈 (E. nana) 的成体组织学与 E. sosorum 相似。表观物种 E. nana 和 E. sosorum 成虫的眼睛看起来发育完全，具有功能齐全的眼睛的所有组织学特征。相比之下，E. rathbuni 成虫的眼睛层次较少，缺乏晶状体和其他与视觉相关的特征，正如之前报道的那样。然而，在早期发育阶段，E. rathbuni 和 E. sosorum 之间的眼睛形态没有显着差异。在形态方面观察到两种表型之间的平行发育；然而，Pax6 标记似乎在 E.rathbuni 的发育后期有所减少。我们测试了视觉色素蛋白视蛋白和视紫红质的免疫标记，并观察了大肠杆菌感光盘周围的免疫定位。 nana 和 E. sosorum，但不在地下 E.rathbuni 中。我们对发育中蝾螈的研究结果表明，发育不全和退化共同导致了成年蝾螈眼睛的缩小。