Morphological Color-Change in the Red-Backed Salamander (Plethodon cinereus) While Kept in Captivity
Coloration is a trait frequently cited as important to ecological, and thus evolutionary, processes in amphibians. To fully understand the impact of coloration, a consistent method of color measurement is required, which is often achieved by collecting color information in a captive, laboratory setting. However, results from the lab can only be generalized to the field if coloration remains consistent between the two. In this study we collected spectral data from two discrete color morphs of Plethodon cinereus (erythristic and striped) at two distinct time periods while in captivity to determine whether and how their coloration changed over time. We found that brightness in both color morphs decreased similarly through time, though the change was most pronounced in the erythristic morph. Additionally, we examined the overall coloration change over time using multivariate change vectors and found that the magnitude (amount) of multivariate color change was significantly greater in the erythristic morph as compared to the striped morph (for cheek color patches). Intriguingly, the direction of color change in color space was oriented similarly among measured regions within each morph, whereas the direction of color change differed between morphs, indicating that while coloration changed for all individuals, how that change occurred was morph-specific. We propose a physiological mechanism that may be responsible for the observed changes, and suggest several additional mechanisms that may influence labile coloration in these salamanders. Additionally, our findings suggest that quantifying color from individuals held in captivity should be used with caution, as color changes observed in a laboratory setting may not reflect what is seen in the field.
(A) Locations of 18 regions where spectra were collected on each animal. Do1–Do6 correspond to the dorsal regions, Ch1 and Ch2 to the left and right cheek regions, La1–La6 to the lateral regions, and Vn1–Vn4 to the four ventral regions. (B) Representative images of each salamander morph: striped morph at top, with erythristic morph below. (C) Average spectra across all body regions for each morph and time point.
Boxplots of brightness at each region and time point. White boxes correspond to the first measurement at each region, while the adjacent gray box corresponds to the second measurement at each region. Asterisks below each region label denotes the significance of the change associated with that region, where (*) P < 0.05 and (**) P < 0.01.
Principal components plot of color variation of Plethodon. Data from erythristic individuals are shaded in gray, while open shapes represent striped individuals. In addition, circles represent individuals from the first time point, while diamonds depict the second measured time point. The least squares mean is displayed for each group. Dotted lines correspond to the striped morph vectors, while the solid lines correspond to erythristic vectors. All data are plotted in the second and third principal components, which represent approximately 79% of the remaining variation after the first principal component (brightness) is removed. Only group means are shown for clarity.
Contributor Notes
Associate Editor: B. Stuart.