Conclusion
Here, we provide mechanistic evidence that gelada chest redness is linked to increased blood flow near the surface of the skin, specifically through increased blood vessel branching in the chest skin in males. Although we did not detect a sex difference in chest skin gene expression related to androgen and estrogen regulation, future research into the correlation between fluctuations in fecal testosterone metabolites and chest redness within males will help determine whether another aspect of hormonal regulation is involved in chest redness signaling. Going forward, we hope to better understand whether increased angiogenesis creates a current-condition signal for males in the cold, high-altitude environment of the Ethiopian highlands by leveraging biomarkers of energy balance or heat loss.