Variation in retinal thickness among Astyanax F₂ hybrids.

(A) Diagram of the eye, retina, and retinal landmarks. Black box indicates an example region where we recorded retinal thickness. (B) Example retinal sections from the eyes of four F₂ hybrids. Scale bar denotes 50 µm and brackets denote individual retinal layers. Cavefish-like retinas (first two panels) were generally thin and may be missing some layers entirely, including the photoreceptor cell layer. Surface fish-like retinas (last two panels) were generally thicker with layers that are well-differentiated and clearly laminated. In some individuals, the retinal pigment epithelium (RPE) was hypopigmented (first and third panels). (C) Retinal thickness among 115 Astyanax SFxCF F₂ hybrids. Yellow bars denote RPEs that were hypopigmented. (D) Box-plots illustrate variance in the thickness of individual retinal layers. The retinal layers shown are: ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), photoreceptor cell layer (PCL), and retinal pigment epithelium (RPE).