Color variation among habitat types in the spiny softshell turtles (Trionychidae: Apalone) of Cuatrociénegas, Coahuila, Mexico

Ground coloration is highly variable in many reptile species. In turtles, ground color may correspond well to the background coloration of the environment and can change over time to match new surroundings in the laboratory. Variable carapace and plastron coloration across three habitat types were investigated in the Black Softshell Turtle, Apalone spinifera atra, by measuring individual components of the RGB (Red, Green, Blue) color system. In general, A. s. atra carapaces were darker in turtles from lagoons than in turtles from playa lakes. Red and green values were significantly different among all pairs of habitat types, but blue values differed only between the playa lakes and lagoons. Mean color components (RG only) for each population were significantly correlated with corresponding values for the bottom substrate, indicating a positive association of carapace and habitat substrate color components. In contrast, plastron ground color RGB channels showed no significant differences between habitat types and no significant correlations with substrate RGB. These results suggest that dorsal background matching in A. s. atra may be responsible for some of the variation in this key taxonomic trait.