Date of Award


Degree Type


Degree Name

Master of Science (MS)

Author's Department


First Advisor

Edward O. Moll


Male Callagur borneoensis exihibit sexual dichromatism and seasonal coloration which is rare among turtles. In the breeding season male's heads are colored white with a scarlet stripe from the occiput to the tip of the snout. After the breeding season they change to drab charcoal-gray to black with a dull orange-yellow stripe. Females and juveniles are a drab brown throughout the year.

This study was performed to determine the mechanisms of this color change at the histological level. Histological preparation of the head revealed a significant increase in vascular tissue just below the epidermis of the stripe area with increased red color.

The white color of the side of the head was attributed to no epidermal melanosomes and thickening of the epidermis. Dermal melanin was found to play a lesser role in determining the darkness of the skin. Dermal melanophores appeared to have a cycle during the color change. In dark phase I, they were the most prominant donating melanosomes to the epidermis. In dark phase II they were the least prominent appearing to donate melanosomes to the epidermis and blood vessels along which they were aggregated. The melanophores of the light phase were slightly more prominent and were not donating any melanosome to the epidermis. The intermediate had more prominent melanophores that were donating melanosomes to the epidermis.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.