Exploratory Characterization of Adaptive Eye Strategies to High-Acceleration Loading in the Great Spotted Woodpecker.

PURPOSE: Woodpeckers often withstand extreme high acceleration during the pecking process, but show no signs of eye injuries. This study seeks to explore what biomechanical adaptations woodpeckers adopt to protect their eyes under such high impact.

METHODS

The morphometric parameter of eyes in the Great Spotted Woodpecker and its control, Eurasian Hoopoe, were observed based on frozen sectioning and Nissl staining. A series of protein expression including β-APP, p-Tau, p-CRMP2, HSP70, and mTOR of the birds' eyes were also obtained using immunofluorescence staining.

RESULTS

The Great Spotted Woodpecker exhibits a denser, ossified sclera and a more complex pecten. β-APP was primarily localized in the outer nuclear layer while p-CRMP2 was predominantly expressed in the GCL, and HSP70 were co-localized with p-Tau in these birds' eyes. Meanwhile, mTOR exhibited distinct expression patterns corresponding to different phases of injury.

CONCLUSION

Two layers of adaptations were found in eyes of woodpeckers. Structurally, ossified sclera and complex pecten contribute to resistance against pecking-induced eye injuries. Molecularly, abnormal aggregation of β-APP and p-Tau in optic nerve cells were prevented by regulating expression of CRMP2, HSP70, and mTOR, thereby reducing damage in the eyes. These results provide a theoretical foundation for the identification, prevention, and mitigation of acceleration-induced eye injuries.