Figure 2.

A schematic summary of the hypothesized links between red feather coloration and mitochondrial function. To produce red feathers, house finches ingest the yellow carotenoid cryptoxanthin and oxidize it to the red pigment 3-hydroxyechinenone. We hypothesized that ketolation efficiency is linked to mitochondrial bioenergetics. By this hypothesis, birds with low mitochondrial function have limited ketolation capacity and produce yellow feathers. Birds with high mitochondrial function have improved ketolation capacity and produce red feathers. (Online version in colour.)