Vertebral and intervertebral defects associated with spinal curvature in the curveback guppy. Histological sections through normal and scoliotic vertebrae are presented for side-by-side comparison. Sections were cut in both the transverse and sagittal planes and stained with a combination of Picrosirius Red and Alcian Blue, which label collagen and sulfated proteoglycans, respectively. (A,C,E) Compared to normal vertebrae, lordotic and kyphotic vertebrae appear thicker and asymmetric in shape (white arrowheads) on the concave face of the spinal curve. This suggests that scoliotic vertebrae are being distorted or actively remodelled in response to biomechanical stress associated with curvature. (B,D,F) Within the intervertebral ligament of both lordotic and kyphotic vertebrae, the fibrous portion of the spongy layer (cf. Figure 6) appears to migrate towards the convex face of the spinal curvature. The white arrow in panel B' and F' indicates the direction of this migration. The displacement of the fibrous portion causes compression of the spongy portion on the convex face and distension on the opposite side (dotted outlines). Abbreviations: ao, aorta; ha, hemal arch; m, axial muscle; na, neural arch; v, vacuole; vc, vertebral centrum; sc, spinal cord. Scale bar equals 250 μm.