Using spectral data to reconstruct evolutionary changes in coloration: carotenoid color evolution in New World orioles.

Abstract

Carotenoid-based colors are thought to play an important signaling role in many animal taxa. However, little is known about evolutionary changes in carotenoid coloration, especially among closely related species. We used a phylogenetic perspective to examine carotenoid color changes within New World orioles (genus Icterus). Oriole color was quantitatively measured using reflectance spectrometry. We found continuous variation from short- to long-wavelength carotenoid colors in extant orioles--perceived by humans as ranging from yellow to scarlet--suggesting that these carotenoid-based colors have evolved as a continuous character. Ancestral state reconstruction suggests that short- and long-wavelength carotenoid colors have evolved independently multiple times, likely from a middle-wavelength ancestor. Although color showed considerable lability, we found a significant amount of phylogenetic signal across the entire genus. This implies that while labile, the colors of closely related taxa tended to resemble each other more than would be expected due to chance. To our knowledge, this is the first study to use quantitative character states derived from reflectance spectra in ancestral state reconstruction. Reflectance spectra provide an unbiased quantitative description of color that allowed us to detect subtle changes among closely related taxa. Using these quantitative methods to score and reconstruct color changes among closely related taxa provides a better understanding of how elaborate animal colors evolve.