Discrete evolutionary color changes in caciques suggest different modes of carotenoid evolution between closely related taxa

Carotenoid-based colors have signaling roles in a range of animal taxa, yet little is known about how carotenoids vary across species or whether overall patterns may vary across genera. The caciques (Cacicus, Clypicterus and Ocyalus; family Icteridae), a group of passerine birds from Central and South America, appear to visually divide into discrete yellow and red color groups. Reflectance spectrometry supported this observation, showing widely separated short and long-wavelength groups corresponding with yellow and red-feathered taxa. Ancestral state reconstructions inferred a yellow ancestral state with two independent changes to red, and no reversals back to yellow. This pattern contrasts with that of another closely related icterid clade, the New World orioles (Icterus), which exhibit a full range of carotenoid colors and have a pattern of evolution that is continuous and extremely labile. To our knowledge, this study is the first to highlight the possibility of different modes of color evolution even among closely related clades. This study also emphasizes the importance of the methods and assumptions of ancestral state reconstruction. In particular, although coloration and other characters can be measured along a continuous scale, they should be reconstructed using discrete methods when data from extant taxa and underlying mechanisms suggest discrete changes.