Spectral reflectance and substrate color-induced melanization in immature and adult Midland painted turtles (Chrysemys picta marginata)

Abstract

An animal’s coloration can be involved in communication and crypsis and change dynamically over time. We studied spectral reflectance of color pattern and substrate color-induced melanization in adult Midland Painted Turtles (Chrysemys picta marginata). Spectral reflectance of the carapace and plastron ground colors and of the red, yellow, and black markings of the head and limbs did not vary between the sexes. Therefore, yellow and red markings of the head and forelimbs seem unlikely to be sexually-selected traits as would be evidenced by differences in brightness between the sexes. Perhaps the color patterns of the head, neck, and shell margins function to break up the outline of an individual. However, we cannot rule out that the markings of the head and neck function in species recognition or evaluation of mate quality. After being laboratory reared for 150 days, the ground color and the spots or stripes of the head and limbs increased in intensity (turtles lightened) but more so in turtles reared on a white substrate when compared to those reared on a black substrate. At day 150, the ground colors of the carapace and plastron and the black blotches of the marginal scutes of the carapace were darker in individuals reared on a black substrate than in those reared on a white substrate. Therefore, adult turtles that travel among habitats with differing substrate colors could shift the degree of darkness of the carapace and skin ground color, thus more closely matching their backgrounds and reducing predation rates.