Morphological and Ontogenetic Skin Color Changes in the American Alligator (Alligator mississippiensis)

To assess skin color change in alligators, we maintained animals in differently lighted environments and also measured skin colors in an ontogenetic series of wild animals. Juvenile alligators maintained in black enclosures exhibited a gradual lightening of skin color when shifted to white enclosures, and these observed changes were reversible. A histological examination of the skins of alligators maintained in dark tanks showed that the dermis exhibited a dense layer of pigmented cells, while samples from the same animals in light environments exhibited a more diffuse pigmented layer. As alligators grow, they exhibit an ontogenetic loss of stripes that may aid in crypsis and predation. Hatchlings have intense black and yellow vertical stripes that darken with age; adults are a more homogenous black/gray color. Since alligators live in temperate climates and adults have lower surface area/volume ratios, which can be detrimental for the absorption of radiant energy, the darker color of larger animals may also aid in thermoregulation. Alligators at the northern end of their range, with colder climates, exhibited darker skin tones, and the ontogenetic extinction of stripes occurred at a more accelerated rate compared to animals in southern, warmer regions, supporting the idea that latitude-dependent ontogenetic color shift has a role in thermoregulation.

Automated summary

This study examines the effect of lighting and environmental factors on the skin color change in alligators. The results show that maintaining juvenile alligators in black enclosures led to a gradual lightening of skin color when shifted to white enclosures. Histological examination revealed differences in the pigmented layer of the skin between dark and light environments. The study also suggests that the ontogenetic loss of stripes in alligators may aid in crypsis and predation. Additionally, the darker color of larger alligators may play a role in thermoregulation, particularly for individuals living in colder climates at the northern end of their range.