Coloration is highly variable but is not always an honest signal in the painted turtle, <i>Chrysemys Picta</i>

Color signals in animals are often honest, containing information about the individual for potential mates or predators. Both males and females may have honest color signals, though female signals are less often assessed for honesty. Different colorimetric traits, such as overall brightness, hue, ultraviolet brightness, or carotenoid chroma, may be assessed by receivers for information. Painted Turtles, Chrysemys picta (Schneider, 1783), are a brightly colored and widely distributed freshwater turtle species with no visible sexual dichromatism, but the function of their coloration is unknown. We assess two populations of Painted Turtles to compare colorimetric traits across and within populations, and to determine whether any color traits correlate with innate immune function. We find that there is greater carotenoid chroma on areas of the shell not typically associated with courtship than on the neck stripes that are thought to have a role in mate choice. We also find that only one measure of coloration in one color patch, the carotenoid chroma of the neck stripes, is correlated with bactericidal capacity, and in only one population. This system provides an example of a common species having vibrant but understudied coloration that may provide insights into unknown functions of color or uncommon sexual selection variation.