Some freshwater turtle species show substrate color-convergence of the dorsal integument, thus facilitating crypsis. Because turtles move among aquatic habitats with variable substrate colors, we tested whether melanization was reversible in juvenile Midland Painted Turtles (Chrysemys picta marginata) and Red-Eared Sliders (Trachemys scripta elegans). We reared individuals as controls (those reared on black or white substrates for 160 days) or as reversal treatments (those reared on black or white substrates for 80 days and then reversed treatments from black to white or white to black). Mean intensity (a measure of total reflectance of the visual spectrum) of the third vertebral scute of the carapace (TVSC) and dorsal head skin (DHS) of black substrate control groups declined (turtles darkened) slightly in C. p. marginata but more so in T. s. elegans. In the white substrate control groups, mean intensity of TVSC and DHS increased (turtles lightened) substantially in both species. During the first 80 days in both species, intensity of the TVSC and DHS of black-white and white-black reversal groups largely paralleled the black and white substrate control groups, respectively. Following reversal of substrates in both species, mean TVSC and DHS intensities of the black-white and white-black reversal groups converged with the white and black substrate control groups, respectively. Therefore, reversal of TVSC and DHS melanization was complete, or nearly complete, by day 160. Therefore, it seems plausible that, in both species, reversible melanization could allow substrate color convergence in juveniles that experience different environments with variable substrate colors.
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